Busbar Technical Specification

Copper busbars are normally part of a larger generation or transmission system. The continuous rating of the main components such as generators, transformers, rectifiers, etc., therefore determine the nominal current carried by the busbars but in most power systems a one to four second short-circuit current has to be accommodated.

The value of these currents is calculated from the inductive reactances of the power system components and gives rise to different maximum short-circuit currents in the various system sections.

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Performance under Short-circuit Conditions

Busbar trunking systems to BS EN 60439-2 are designed to withstand the effects of short-circuit currents resulting from a fault at any load point in the system, e.g. at a tap off point or at the end of a feeder run.
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Rating under Short-circuit Conditions

The withstand ability will be expressed in one or more of the following ways:

1. short-time withstand rating (current and time)
2. peak current withstand rating
3. conditional short-circuit rating when protected by a short-circuit protective device (s.c.p.d.)

These ratings are explained in more detail:

1. Short-time Withstand Rating

This is an expression of the value of rms current that the system can withstand for a specified period of time without being adversely affected such as to prevent further service. Typically the period of time associated with a short-circuit fault current will be 1 second, however, other time periods may be applicable.

The rated value of current may be anywhere from about 10kA up to 50kA or more according to the construction and thermal rating of the system.

2. Peak Current Withstand Rating

This defines the peak current, occurring virtually instantaneously, that the system can withstand, this being the value that exerts the maximum stress on the supporting insulation.

In an A.C. system rated in terms of short-time withstand current the peak current rating must be at least equal to the peak current produced by the natural asymmetry occurring at the initiation of a fault current in an inductive circuit. This peak is dependent on the power-factor of the circuit under fault conditions and can exceed the value of the steady state fault current by a factor of up to 2.2 times.

3. Conditional Short-circuit Rating

Short-circuit protective devices (s.c.p.ds) are commonly current-limiting devices; that is they are able to respond to a fault current within the first few milliseconds and prevent the current rising to its prospective peak value. This applies to HRC fuses and many circuit breakers in the instantaneous tripping mode. Advantage is taken of these current limiting properties in the rating of busbar trunking for high prospective fault levels. The condition is that the specified s.c.p.d. (fuse or circuit breaker) is installed up stream of the trunking. Each of the ratings above takes into account the two major effects of a fault current, these being heat and electromagnetic force.

The heating effect needs to be limited to avoid damage to supporting insulation. The electromagnetic effect produces forces between the busbars which stress the supporting mechanical structure, including vibrational forces on A.C. The only way to verify the quoted ratings satisfactorily is by means of type tests to the British Standard.
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Type Testing

Busbar trunking systems are tested in accordance with BS EN 60439-2 to establish one or more of the short circuit withstand ratings defined above. In the case of short-time rating the specified current is applied for the quoted time. A separate test may be required to establish the peak withstand current if the quoted value is not obtained during the short-time test. In the case of a conditional rating with a specified s.c.p.d. the test is conducted with the full prospective current value at the trunking feeder unit and not less than 105% rated voltage, since the s.c.p.d. (fuse or circuit breaker) will be voltage dependent in terms of let through energy.
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Application

It is necessary for the system designer to determine the prospective fault current at every relevant point in the installation by calculation, measurement or based on information provided e.g. by the supply authority. The method for this is well established, in general terms being the source voltage divided by the circuit impedance to each point. The designer will then select protective devices at each point where a circuit change occurs e.g. between a feeder and a distribution run of a lower current rating. The device selected must operate within the limits of the busbar trunking short-circuit withstand.

The time delay settings of any circuit breaker must be within the specified short time quoted for the prospective fault current. Any s.c.p.d. used against a conditional short-circuit rating must have energy limitation not exceeding that of the quoted s.c.p.d. For preference the s.c.p.d. recommended by the trunking manufacturer should be used.
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Voltage Drop

The requirements for voltage-drop are given in BS 7671: Regulation 525-01-02. For busbar trunking systems the method of calculating voltage drop is given in BS EN 60439-2 from which the following guidance notes have been prepared.

Voltage Drop

Figures for voltage drop for busbar trunking systems are given in the manufacturer’s literature.

The figures are expressed in volts or milli-volts per metre or 100 metres, allowing a simple calculation for a given length of run.

The figures are usually given as line-to-line voltage drop for a 3 phase balanced load.

The figures take into account resistance to joints and temperature of conductors and assume the system is fully loaded.

Standard Data

BS EN 60439-2 requires the manufacturer to provide the following data for the purposes of calculation, where necessary:

R²⁰ the mean ohmic resistance of the system, unloaded, at 20ºC per metre per phase

X the mean reactance of the system, per metre per phase

For systems rated over 630A:

R^T the mean ohmic resistance when loaded at rated current per metre per phase

Application

In general the voltage drop figures provided by the manufacturer are used directly to establish the total voltage drop on a given system; however this will give a pessimistic result in the majority of cases.

Where a more precise calculation is required (e.g. for a very long run or where the voltage level is more critical) advantage may be taken of the basic data to obtain a more exact figure.

1. Resistance – the actual current is usually lower than the rated current and hence the resistance of the conductors will be lower due to the reduced operating temperature.
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   Rx = R20 [1+0.004(Tc - 20)] ohms/metre and Tc is approximately Ta + Tr

   where Rx is the actual conductor resistance

   Ta is the ambient temperature

   Tr is the full load temperature rise in ºC (assume say 55ºC)

2. Power factor – the load power factor will influence the voltage drop according to the resistance and reactance of the busbar trunking itself.
   The voltage drop line-to-line ( Δv) is calculated as follows:

   Δv = √ 3 I (R x cos Φ + X sin Φ) volts/metre

   where I is the load current

   R_x is the actual conductor resistance (Ω/m)

   X is the conductor reactance (Ω/m)

   Cos Φ is the load power factor

   sin Φ = sin (cos-1 Φ )

3. Distributed Load – where the load is tapped off the busbar trunking along its length this may also be taken into account by calculating the voltage drop for each section. As a rule of thumb the full load voltage drop may be divided by 2 to give the approximate voltage drop at the end of a system with distributed load.
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4. Frequency – the manufacturers data will generally give reactance (X) at 50Hz for mains supply in the UK. At any other frequency the reactance should be re-calculated.
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   X_f = x F/50
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   where X_f is the reactance at frequency F in Hz

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Source: Siemens Barduct Busbar Specification

Dry-Type disc wound transformers in MV applications

Medium voltage, dry-type transformers may have their high voltage windings constructed using either the layer winding technique or the disc winding technique.

Both winding techniques provide the same result in terms of electrical performance parameters, i.e. turns ratio, impedance etc.

However, the use of transformers employing disc wound high voltage windings can result in increased reliability and therefore reduced downtime.

Introduction

The basic purpose of a transformer is to convert electricity at one voltage to electricity at another voltage, either of higher or lower value. In order to achieve this voltage conversion, coils are wound on a laminated silicon steel core which provides a path for the magnetic flux. The coils comprise a number of turns of conductor, either copper or aluminum, wound as two electrically separate windings, called the primary winding and the secondary winding. The primary winding is connected to the source of voltage while the secondary winding is connected to the load. The ratio of primary to secondary turns is the same as the required ratio of primary to secondary voltages.

The turns of conductor forming the primary and secondary windings must be insulated from one another, while the primary winding must be insulated from the secondary winding and both the primary and secondary windings must be insulated from ground. The insulation of turns and windings is collectively called the insulation system of the transformer. The insulation system must be designed to withstand the effects of lightning strikes and switching surges to which the transformer is subjected, in addition to the normal operating voltages. A further requirement of the insulation system is that it must withstand the environmental conditions to which it is exposed, such as moisture, dust etc. A variety of techniques and materials are employed to achieve the necessary performance characteristics of the insulation system.

Layer winding

Fig.1 Layer winding

For low voltage, i.e. 600 Volt class windings, the winding technique used almost exclusively is the layer winding technique, also sometimes called helical winding or barrel winding. In this technique, the turns required for the winding are wound in one or more concentric layers connected in series, with the turns of each layer being wound side by side along the axial length of the coil until the layer is full. The conductors of the winding are insulated and so between turns there will be a minimum of two thicknesses of insulation. Between each pair of layers there will be layers of insulation material and/or an air duct.

Low voltage windings will generally be wound top to bottom, bottom to top etc. using a continuous conductor, until all layers are complete. High voltage windings, i.e. above 600 Volt class, may be wound in the same way, provided the voltage between layers is not too great.

To reduce the voltage stress between layers, high voltage windings are often wound in only one direction, for example, top to bottom. When the first layer of winding is complete, the winding conductor is laid across the completed layer from bottom to top and then the next layer is wound, again from top to bottom. In this way, the voltage stress between layers is halved.

The conductor must, of course, have additional insulation where it crosses the winding from bottom to top.

Fig.2 Transformer with layer wound coils

Disc winding

In the disc winding, the required number of turns are wound in a number of horizontal discs spaced along the axial length of the coil. The conductor is usually rectangular in cross-section and the turns are wound in a radial direction, one on top of the other i.e. one turn per layer, until the required number of turns per disc has been wound.

Fig.3 Disc winding

The conductor is then moved to the next disc and the process repeated until all turns have been wound. There is an air space, or duct, between each pair of discs. The disc winding requires insulation only on the conductor itself, no additional insulation is required between layers, as in the layer winding.

The disc wound high voltage winding is usually wound in two halves, in order that the required voltage adjustment taps may be positioned at the electrical center of the winding. In this way the magnetic, or effective length of the winding is maintained, irrespective of which tap is used, and therefore the magnetic balance between primary and secondary windings is always close to its optimum.

This is essential to maintain the short circuit strength of the winding, and reduces the axial electromagnetic forces which arise when the windings are not perfectly balanced.

Fig.4 Transformer with disc wound coils

Characteristics of Layer wound coils

As stated previously, the layer wound coil requires insulation between layers, in addition to the conductor insulation. The thickness of insulation required will depend upon the voltage stress between layers, and comprises one or more thicknesses of the appropriate insulation material. In practice, due to the nature of the construction of a layer wound coil, the finished coil will have several unavoidable small air pockets between turns and between layers. Many of these air pockets will become filled with resin during vacuum pressure impregnation of the coil.

Fig. 5 Equivalent circuit for Impulse voltage distribution

However, it sometimes happens that some air pockets remain and it is in these air pockets that partial discharges can occur, greatly increasing the possibility of premature aging of the insulation and eventual failure.

Catastrophic failure can occur within a few months of energization. Under short circuit conditions, the electromagnetic forces developed cause transformer windings to attempt to telescope. At the same time the coil end blocking is trying to prevent movement. The result is often that the turns of the winding have a tendency to slip over one another, causing turn-to turn failure, due to abrasion of the insulation as the turns rub together. A further disadvantage of the layer wound coil is its poor impulse voltage distribution between the first few turns of the winding, due to the high ground capacitance and the low series capacitance.

A transformer winding forms a complex network of resistance, inductance and capacitance. As far as the impulse voltage distribution is concerned, the resistance can be ignored and at the instant of application of the impulse wave, when very high frequencies are predominant, the inductive elements become effectively infinite impedances. The whole structure therefore reduces to a capacitive network (see fig.5). Each turn of a transformer winding is insulated with a dielectric material and can be thought of as one plate of a multiple plate capacitor. In addition, the combination of dielectric material and air between each turn and ground forms further capacitive elements.

Characteristics of Disc wound coils

The major advantage of the disc wound coil lies in its open construction and relative lack of insulation. For a 15kV class transformer employing a disc wound primary winding, the number of discs will typically be in the range 36 to 48, resulting in a relatively low voltage per disc. Since each disc is separated from the next by an air space, the voltage stress between discs can easily be handled by the combination of conductor insulation and air, no additional insulation being necessary.

Each disc comprises a number of turns with each turn occupying one layer, i.e. one turn per layer: the voltage stress between layers is therefore the same as the voltage stress between turns and again, can easily be handled by the conductor insulation. The turns of each disc, being wound tightly together provide almost no possibility of air pockets being present within the disc.

Due to the open construction of the discs, any small air pockets which may be present are readily filled with resin during vacuum pressure impregnation of the coil. A properly designed and manufactured dry-type transformer disc winding therefore displays very low values of partial discharge, typically in the range 10 to 20 picocoulombs.

Unlike the layer wound coil, the disc wound coil provides good impulse voltage distribution, due to its inherently low value of ground capacitance and high series capacitance. The disc wound coil also displays excellent short circuit strength. Each disc by itself is mechanically very strong and the complete assembly of discs are held very securely in place. While the electromagnetic forces resulting from a short circuit result in a tendency, for the windings to telescope, the high voltage turns usually remain intact relative to each other. Instead, the complete disc has a tendency to distort as an assembly, with all the turns distorting by the same amount. The transformer can often continue to function, despite the distortion, until a convenient time arises for repair.

Losses/heat

The flow of electric current through the turns of a transformer winding causes power losses which manifest themselves in the form of heat. These losses are called ‘’load losses’’ and are proportional to the square of the current. Obviously, it is necessary to dissipate this heat, to prevent overheating of the transformer, and in a dry-type transformer, this is achieved by the use of air spaces, or ducts, within the winding. The layer wound coil relies on vertical air ducts between layers and between windings, for cooling. Cool air enters the air ducts at the bottom of the coil and by natural convection, rises through the ducts, collecting heat on its way, then exits the coil at the top. It is essential for proper operation of the transformer that these air ducts are kept clear at all times.

The insulation required between the layers of a layer wound coil has a tendency to thermally lag the winding, impeding the dissipation of heat. The greater the operating voltage of the winding, the greater is the amount of insulation required and the greater is the lagging effect of the insulation. Some radiation also takes place from the outer surfaces of the coils. The open nature of the disc wound coil greatly improves the transfer of heat from the winding to the surrounding air. The thermal lagging effect of insulation is removed and the multiple horizontal air spaces between discs provide a large surface area for cooling by both radiation and convection.

Conclusions

The combination of layer wound low voltage winding, disc wound high voltage winding, NOMEX insulation and vacuum pressure impregnation of the windings with a solventless epoxy resin, results in a very reliable transformer with a long life expectancy. Transformers constructed in this way will be relatively free from partial discharge and will provide excellent impulse strength and short circuit strength, vital requirements for reliable operation in the most demanding of applications.

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Author: Derek Foster, Olsun Electrics Corporation

Maintenance Of High Voltage Circuit Breakers

Most manufacturers recommend com­plete inspections, external and internal, at intervals of from 6 to 12 months.

Ex­perience has shown that a considerable expense is involved, some of which may be unnecessary, in adhering to the manufacturer’s recommendations of in­ ternal inspections at 6 to 12 month intervals. With proper external checks, part of the expense, delay, and labor of internal inspections may be avoided without sacrifice of dependability.
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Inspection schedule for new breakers

A temporary schedule of frequent inspections is necessary after the erection of new equipment, the modification or modernization of old equipment, or the replication of old equipment under different condi­ tions.

The temporary schedule is required to Correct internal defects which ordinarily appear in the first year of service and to correlate external check procedures with internal conditions as a basis for more conservative maintenance program thereafter. Assuming that a circuit breaker shows no serious defects at the early complete inspections and no heavy interrupting duty is imposed, the following inspection schedule is recommended:

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Inspection schedule for existing breakers

The inspection schedule should be based by the interrupting duty imposed on the breaker. It is advisable to make a complete internal inspection after the first severe fault interruption. If internal conditions are satisfactory, progressively more fault interruptions may be allowed before an internal inspection is made. Average experience indicates that up to five fault interruptions are allowable between inspections on 230 kV and above circuit breakers, and up to 10 fault interruptions are allowable on circuit breakers rated under 230 kV.

Normally, no more than 2 years should elapse between external in­ spections or 4 years between internal inspections.

External Inspection Guide

The following items should be included in an external inspection of a high-voltage breaker.

1. Visually inspect PCB externals and operating mechanism. The tripping latches should be examined with spe­ cial care since small errors in adjustments and clearances and roughness of the latching surfaces may cause the breaker to fail to latch properly or increase the force neces­ sary to trip the breaker to such an extent that electrical tripping will not always be successful, especially if the tripping voltage is low. Excessive „opening“ spring pressure can cause excessive friction at the tripping latch and should be avoided. Also, some extra pressure against the tripping latch may be caused by the electro­ magnetic forces due to flow of heavy short-circuit currents through the breaker.
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   Lubrication of the bearing surfaces of the operating mechanism should be made as recommended in the manufacturer’s instruction book, but excessive lubrication should be avoided as oily surfaces collect dust and grit and get stiff in cold weather, resulting in excessive friction.
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2. Check oil dielectric strength and color for oil breakers. The dielectric strength must be maintained to pre vent internal breakdown under voltage surges and to enable the interrupter to function properly since its action depends upon changing the internal arc path from a fair conductor to a good insulator in the short interval while the current is passing through zero. Manufacturer’s instructions state the lowest allowable dielectric strength for the various circuit break­ ers. It is advisable to maintain the dielectric strength above 20 kV even though some manufacturer’s instructions allow 16 kV.
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   If the oil is carbonized, filtering may remove the suspended particles, but the interrupters, bushings, etc., must be wiped clean. If the dielectric strength is lowered by moisture, an inspection of the fiber and wood parts is advisable and the source of the moisture should be corrected. For these reasons, it is rarely worthwhile to filter the oil in a circuit breaker while it is in service.
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3. Observe breaker operation under load.
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4. Operate breaker manually and electrically and observe for malfunc­ tion. The presence of excessive friction in the tripping mechanism and the margin of safety in the tripping function should be determined by making a test of the minimum voltage required to trip the breaker. This can be accomplished by connecting a switch and rheostat in series in the trip-coil circuit at the breaker (across the terminals to the remote control switch) and a voltmeter across the trip coil. Staring with not over 50 percent of rated trip-coil voltage, gradually in­ crease the voltage until the trip-coil plunger picks up and successfully trips the breaker and record the mini­ mum tripping voltage. Most breakers should trip at about 56 percent of rated trip-coil voltage.
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   The trip-coil re­ sistance should be measured and compared with the factor test value to disclose shorted turns.
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   Most modern breakers have trip coils which will overheat or burn out if left energized for more than a short pe­ riod. An auxiliary switch is used in series with the coil to open the circuit as soon as the breaker has closed. The auxiliary switch must be properly adjusted and successfully break the arc without damage to the contacts.
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   Tests should also be made to deter­ mine the minimum voltage which will close the breaker and the closing coil resistance.
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5. Trip breaker from protective relays.
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6. Check operating mechanism adjustments. Measurements of the mechanical clearances of the operat­ing mechanism associated with the tank or pole should be made. Appre­ ciable variation between the value found and the setting when erected or after the last maintenance overhaul is erected or after the last maintenance overhaul is usually an indication of mechanical trouble. Temperature and difference of temperature between different parts of the mechanism effect the clearances some. The manufacturers’ recommended tolerances usually allow for these effects.
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7. Doble test bushings and breaker.
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8. Measure contact resistance. As long as no foreign material is present, the contact resistance of high-pres- sure, butt-type contacts is practically independent of surface condition. Nevertheless, measurement of the electrical resistance between external bushing terminals of each pole may be regarded as the final „proof of the pudding.“ Any abnormal increase in the resistance of this circuit may be an indication of foreign material in contacts, contact loose in support, loose jumper, or loose bushing connection. Any one of these may cause localized heating and deterioration.
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   The amount of heat above normal may be readily calculated from the increase in resistance and the current.Resistance of the main contact cir­ cuits can be most conveniently measured with a portable double bridge (Kelvin) or a „Ducter.“ The breaker contacts should not be opened during this test because of possible damage to the test equip­ment.
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   Table 1 gives maximum contact resistances for typical classes of breakers.
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9. Make time-travel or motion-analyzer records. Circuit breaker motion an­ alyzers are portable devices designed to monitor the operation of power circuit breakers which permit mechanical coupling of the motion an­ alyzer to the circuit breaker operating rod. These include high-voltage and extra- high-voltage dead tank and SF6 breakers and low-voltage air and vac­ uum circuit breakers.
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   Motion analyzers can provide graphic records of close or open initiation signals, contact closing or opening time with respect to initiation signals, contact movement and velocity, and contact bounce or rebound. The records obtained not only indicated when mechanical difficulties are present but also help isolate the cause of the difficulties. It is preferable to obtain a motion-analyzer record on a breaker when it is first installed. This will provide a master record which can be filed and used for comparison with future maintenance checks.
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   Tripping and closing voltages should be re­ corded on the master record so subsequent tests can be performed under comparable conditions. Time-travel records are taken on the pole nearest the operating mecha­ nism to avoid the inconsistencies due to linkage vibration and slack in the remote phases..
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Internal Inpection Guide – Lines

An internal inspection should include all items listed for an external inspection, plus the breaker tanks or contact heads should be opened and the contacts nd interrupting parts should be inspected. These guidelines are not intended to be a complete list of breaker maintenance but are intended to provide an idea of the scope of each inspection.
A specific checklist should be developed in the field for each type of inspection for each circuit breaker maintained.
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Typical Internal Breaker Problems

The following difficulties should be looked for during internal breaker inspections:

• Tendency for keys, bolts (espe- cially fiber), cotter pins, etc, to come loose.
• Tendency for wood operating rods, supports, or guides to come loose from clamps or mountings.
• Tendency for carbon or sludge to form and accumulate in interrupter or on bushings.
• Tendency for interrupter to flash over and rupture static shield or resis­ tor.
• Tendency for interrupter parts or barriers to burn or erode.
• Tendency for bushing gaskets to leak moisture into breaker insulating material.

Fortunately, these difficulties are most likely to appear early in the use of a breaker and would be disclosed by the early internal inspections. As unsatis­ factory internal conditions are corrected and after one or two inspections show the internal conditions to be satisfactory, the frequency of internal inspections may safely be decreased.

Influence Of Duty Imposed

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Influence of light duty

Internal inspection of a circuit breaker which has had no interruption duty or switching since the previous inspection will not be particularly beneficial although it will not be a total loss. If the breaker has been energized, but open, erosion in the form or irregular grooves (called tracking) on the inner surface of the interrupter or shields may appear due to electrostatic charging current. This is usually aggravated by a deposit of carbon sludge which has previously been generated by some interrupting operation.
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If the breaker has remained closed and carrying current, evidence of heating of the contacts may be found if the contact surfaces were not clean, have oxidized, or if the contact pressure was improper. Any shrinkage and loosening of wood or fiber parts (due to loss of absorbed moisture into the dry oil) will take place following erection, whether the breaker is operated or not. Mechanical operation, however, will make any loosening more evident. It is worthwhile to deliberately impose several switching operations on the breaker before inspection if possible. If this is impossible, some additional information may be gained by operating the breaker several times after it is deenergized, measuring the contact resistance of each pole initially and after each operation.
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Influence of normal duty

The relative severity of duty imposed by load switching, line dropping, and fault interruptions depends upon the type of circuit breaker involved. In circuit breakers which employ an oil blast generated by the power arc, the interruption of light faults or the interruption of line charging current may cause more deterioration than the interruption of heavy faults within the rating of the breaker because of low oil pressure. In some designs using this basic principle of interruption, distress at light interrupting duty is minimized by multiple breaks, rapid contact travel, and turbulence of the oil caused by movement of the contact and mech­ anism.

In designs employing a mechanically driven piston to supple­ ment the arc-driven oil blast, the performance is more uniform. Still more uniform performance is usually yielded by designs which depend for arc interruption upon an oil blast driven by mechanical means. In the latter types, erosion of the contacts may appear only with heavy interruptions. The mechanical stresses which accompany heavy interruptions are always more severe.

These variations of characteristic performance among various designs must be considered when judging the need for maintenance from the service records and when judging the performance of a breaker from evidence on inspection. Because of these variations, the practice of evaluating each fault interruption as equivalent to 100 no-load operations, employed by some companies, is necessarily very approximate although it may be a useful guide in the absence of any other information.
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Influence of severe duty

Erosion of the contacts and damage from severe mechanical stresses may occur during large fault interruption. The most reliable indication of the stress to which a circuit breaker is subjected during fault interruptions is afforded by automatic oscillograph records. Deterioration of the circuit breaker may be assumed to be proportional to the energy dissipated in the breaker during the interruption.

The energy dissipated is approximately proportional to the current and the duration of arcing; that is, the time from parting of the contacts to interruption of the current. However, the parting of contacts is not always evident on the oscillograms, and it is sometimes necessary to determine this from indicated relay time and the known time for breaker contacts to part. Where automatic oscillograph records are available, they may be as useful in guiding oil circuit breaker maintenance as in showing relay and system performance.

Where automatic oscillographs are not available, a very approximate, but nevertheless useful, indication of fault duty imposed on the circuit breakers may be obtained from relay operation targets and accompanying system conditions. All such data should be tabulated in the circuit breaker maintenance file.
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SOURCE: HYDROELECTRIC RESEARCH AND TECHNICAL SERVICES GROUP

Simulacija rada dvostrano napajanog asinhronog motora

Automatizacija proizvodnih procesa uslovila je potrebu za stalnim usavršavanjem regulisanih elektromotornih pogona od kojih se zahtevaju pogodne regulacione karakteristike, smanjenje utroška električne energije, povećana pouzdanost, smanjenje tekućeg održavanja i dr.

Neke statistike ukazuju na to da se u razvijenim zemljama preko polovine proizvedene električne energije pretvara u mehaničku energiju u elektromotornim pogonima. Poslednjih godina se, dugo nezamenljivi koncept regulisanih pogona baziran na mašinama jednosmerne struje (DC) , zamenjuje regulisanim mašinama naizmenične struje (AC). Široka rasprostranjenost pogona sa mašinama jednosmerne struje uslovljena je mogućnošću raspregnutog upravljanja fluksom i momentom mašine uz relativno jednostavan elektronski izvor napajanja. Razvojem statičkih pretvarača i teorije vektorskog upravljanja mašine naizmenične struje sve više istiskuju jednosmerne zahvaljujući prednostima koje do sada nisu mogle da dođu do izražaja kao što su : nepostojanje komutatora, jednostavnost, robustnost i to što, gotovo da, im nije potrebno održavanje.

Jedna od mogućnosti regulisanja brzine asinhronog motora sa namotanim rotorom je pomoću dvostranog napajanja. Sa jedne strane, asinhroni motor, napajamo iz mreže. Mrežna učestanost i amplituda napona su konstantni, sa druge strane motor napajamo iz regulisanog izvora čiju je učestanost i amplitudu moguće menjati. Asinhroni motor sa dvostranim napajanjem u sinhronom režimu rada radi kao sinhrona mašina kojoj se može regulisati brzina. Brzina obrtanja se zadaje jednom učestanošću napajanja i nezavisna je od opterećenja. Pri tome, brzina može da se reguliše i u jednom i u drugom smeru, iznad i ispod sinhrone brzine a mašina može da radi ili kao motor ili kao generator.

Mogućnost regulisanja brzine obrtanja asinhronog motora dvostranim napajanjem uočena je još početkom ovog veka [ 1 ]. Dugo vremena ovaj način regulacije brzine nije našao širu primenu zbog problema vezanih za izvor promenljive učestanosti. Razvojem poluprovodničkih prtevarača omogućeno je da ovaj način regulisanja brzine dobije širu primenu, s’ obzirom na ostale dobre osobine koje poseduje.
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Kratak sadržaj rada

Tema ovog rada je „Simulacija rada dvostrano napajanog asinhronog motora“. Simulacija je realizovana uz pomoć simulacionog programskog paketa VisSim. VisSim je program, baziran na Windows okruženju, za modelovanje i simuliranje složenih dinamičkih sistema. On je spoj jednostavnog vizelnog rešavanja problema potpomognutog moćnim simulatorom. Vizuelni blok dijagrami omogućavaju pojednostavljeno rešavanje i prepravljanje složenih problema, dok moćni simulator omogućava brzo i precizno rešavanje linearnih, nelinearnih, kontinualnih i diskretnih problema. VisSim je simulacioni program koji ne zahteva linijsko pisanje programa, pregledan je, ima moćan matematički aparat.

Sve su ovo razlozi koji olakšavaju njegovu upotrebu i štede vreme onome ko ih koristi. Nešto više možete saznati o ovom simulacionom programu na web sajtu čija je adresa: www.vissim.com . Izrada simulacionog programa zahtevala je modelovanje konfiguracije prikazane uprošćenom zamenskom šemom na sledećoj slici:

Slika 1. Uprošćena zamenska šema celokupne konfiguracije

Zbog pojednostavljenja simulacije, modelovan je samo trofazni asinhroni motor u uslovima dvostranog napajanja odnosno sama dinamika prelaznih procesa koji se odigravaju pri tome. U okviru simulacionog programa zadaje se željena brzina obrtanja dok se veličine učestanosti i amplitude napona napajanja, sa strane regulisanog izvora napajanja, proračunavaju na osnovu zadate brzine.

Narednim poglavljima obrađena je kako problematika regulisanja brzine obrtanja dvostrano napajanih asinhronih trofaznih mašina tako i analiza svih važnih detalja vezanih za modelovanje samog procesa. Sva razmatranja u ovom radu su sprovedena za slučaj da se napajanje sa strane statora vrši iz mreže a napajanje sa strane rotora iz regulisanog izvora promenljive učestanosti i amplitude napona. Svi izvedeni zaključci bi važili i za obrnut slučaj.
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2.1 Analitička teorija asinhronog motora sa dvostranim napajanjem

2.1.1 Regulisanje brzine asinhronog motora dvostranim napajanjem

Regulisanje brzine i smera obrtanja asinhronog motora sa namotanim rotorom pomoću dvostarnog napajanja zasniva se na promeni učestanosti i napona sa jedne strane, uz konstantnu učestanost i konstantan napon sa druge strane. Najčešće su napon i učestanost sa strane statora stalni i on se napaja iz mreže dok se napajanje sa strane rotora vrši preko regulisanog poluprovodničkog pretvarača, promenljive učestanosti i napona. Najčešća su dva rešenja.

Jedno rešenje tj. uprošćena blok šema konfiguracije sa jednosmernim međukolom prikazana je na slici ispod:

Slika 2. Konfiguracija sa jednosmernim međukolom

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dok je uprošćena blok šema drugog rešenja sa ciklokonvertorom prikazana na narednoj slici:

slika 3. Konfiguracija sa ciklokonvertorom

Kao izvor promenljivog napona i učestanosti moguće je upotrebiti i poseban sinhroni generator. Mada se ovo rešenje gotovo i ne koristi.

Brzina obrtanja asinhronog motora iznosi :

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odnosno, gde su:
n₁ – sinhrona brzina
n – brzina obrtanja
s – klizanje,
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a kako je : 

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to je : 

Pošto se, u opštem slučaju, obrtne magnetopobudne sile statora i rotora mogu obrtati u istom ili u različitim smerovima to je:

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Na sledećoj slici je prikazana zavisnost brzine obrtanja rotora od učestanosti rotorskih veličina, pri konstantnoj, mrežnoj učestanosti.

Slika 4. Zavisnost brzine obrtanja od rotorske učestanosti

Pri tome se deo dijagrama, sa slike, koji odgovara negativnoj učestanosti odnosi na slučaj kada se obrtne magnetopobudne sile statora i rotora obrću u suprotnim smerovima. Deo koji odgovara pozitivnoj učestanosti je slučaj kada se obrtne magnetopobudne sile obrću u istom smeru.

Odavde se vidi da je dvostranim napajanjem moguće regulisati brzinu obrtanja asinhronog motora u jednom i u drugom smeru, ispod i iznad sinhrone brzine. Pri f₁ = f₂ brzina obrtanja može biti jednaka nuli ili dvostrukoj sinhronoj brzini, u zavisnosti od međusobnih smerova obrtanja magnetopobudnih sila.
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2.1.2 Osnovne jednačine i ekvivalentna šema asinhronog motora sa dvostranim napajanjem

Osnovne jednačine asinhronog motora sa dvostranim napajanjem mogu se dobiti polazeći od osnovnih jednačina asinhronog motora za standradni režim rada, uzimajući u obzir i napajanje sa strane rotora:

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Ukoliko uzmemo u obzir da je:

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nakon deljenja jednačina ( 2.1 ) i ( 2.2 ) klizanjem dobijamo sledeće:

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Uzimajući u obzir da je:

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dobijamo sledeće :

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Zanemarujući gubitke u gvožđu (Z_m ≈ jX_m):

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Izrazi ( 2.7 ) i ( 2.8 ) se mogu predstaviti u jednom praktičnijem obliku ukoliko uzmemo u obzir da je I₀ = I₁ + I₂ imamo:

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gde je

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Na osnovu dobijenih izraza ekvivalentna šema dvostrano napajanog asinhronog motora ima sledeći izgled:

Slika 5. Ekvivalentna šema dvostrano napajanog asinhronog motora

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Uskoro u nastavku stručnog teksta: Simulacija rada dvostrano napajanog asinhronog motora (2)

• Simulacioni VisSim model dvostrano napajanog asinhronog motora
• Zaključak

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AUTOR STRUČNOG TEKSTA:

Jovica Vranjković
Diplomski rad: Simulacija rada dvostrano napajanog asinhronog motora
Univerzitet u Beogradu Elektrotehnički fakultet Katedra za energetske pretvarače i pogone

How Wind Turbines Work

Wind is a form of solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth’s surface, and rotation of the earth. Wind flow patterns are modified by the earth’s terrain, bodies of water, and vegetation. Humans use this wind flow, or motion energy, for many purposes: sailing, flying a kite, and even generating electricity.

The terms wind energy or wind powmegawatts.er describe the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy in the wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity.

So how do wind turbines make electricity? Simply stated, a wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. Take a look inside a wind turbine to see the various parts. View the wind turbine animation to see how a wind turbine works.

Wind turbines operate on a simple principle. The energy in the wind turns two or three propeller-like blades around a rotor. The rotor is connected to the main shaft, which spins a generator to create electricity. Wind turbines are mounted on a tower to capture the most energy.

At 100 feet (30 meters) or more above ground, they can take advantage of faster and less turbulent wind.

Wind turbines can be used to produce electricity for a single home or building, or they can be connected to an electricity grid (shown here) for more widespread electricity distribution.

This aerial view of a wind power plant shows how a group of wind turbines can make electricity for the utility grid. The electricity is sent through transmission and distribution lines to homes, businesses, schools, and so on.

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Types of Wind Turbines

Modern wind turbines fall into two basic groups: the horizontal-axis variety, as shown in the photo, and the vertical-axis design, like the eggbeater-style Darrieus model, named after its French inventor.

Horizontal-axis wind turbines typically either have two or three blades. These three-bladed wind turbines are operated „upwind,“ with the blades facing into the wind.
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Sizes of Wind Turbines

Utility-scale turbines range in size from 100 kilowatts to as large as several megawatts. Larger turbines are grouped together into wind farms, which provide bulk power to the electrical grid.

Single small turbines, below 100 kilowatts, are used for homes, telecommunications dishes, or water pumping. Small turbines are sometimes used in connection with diesel generators, batteries, and photovoltaic systems.

These systems are called hybrid wind systems and are typically used in remote, off-grid locations, where a connection to the utility grid is not available.

Many wind farms have sprung up in the Midwest in recent years, generating power for utilities. Farmers benefit by receiving land lease payments from wind energy project developers.

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GE Wind Energy's 3.6 megawatt wind turbine is one of the largest prototypes ever erected. Larger wind turbines are more efficient and cost effective.

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Inside the Wind Turbine

Inside the Wind Turbine

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Anemometer:

Measures the wind speed and transmits wind speed data to the controller.

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Blades:

Most turbines have either two or three blades. Wind blowing over the blades causes the blades to „lift“ and rotate.

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Brake:

A disc brake, which can be applied mechanically, electrically, or hydraulically to stop the rotor in emergencies.

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Controller:

The controller starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and shuts off the machine at about 55 mph. Turbines do not operate at wind speeds above about 55 mph because they might be damaged by the high winds.

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Gear box:

Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1000 to 1800 rpm, the rotational speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of the wind turbine and engineers are exploring „direct-drive“ generators that operate at lower rotational speeds and don’t need gear boxes.

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Generator:

Usually an off-the-shelf induction generator that produces 60-cycle AC electricity.

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High-speed shaft:

Drives the generator.

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Low-speed shaft:

The rotor turns the low-speed shaft at about 30 to 60 rotations per minute.

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Nacelle:

The nacelle sits atop the tower and contains the gear box, low- and high-speed shafts, generator, controller, and brake. Some nacelles are large enough for a helicopter to land on.

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Pitch:

Blades are turned, or pitched, out of the wind to control the rotor speed and keep the rotor from turning in winds that are too high or too low to produce electricity.

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Rotor:

The blades and the hub together are called the rotor.

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Tower:

Towers are made from tubular steel (shown here), concrete, or steel lattice. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity.

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Wind direction:

This is an „upwind“ turbine, so-called because it operates facing into the wind. Other turbines are designed to run „downwind,“ facing away from the wind.

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Wind vane:

Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind.

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Yaw drive:

Upwind turbines face into the wind; the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. Downwind turbines don’t require a yaw drive, the wind blows the rotor downwind.

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Yaw motor:

Powers the yaw drive.

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SOURCE: U.S. Department Of Energy | How Wind Turbines Work

EES Kvalitet električne energije - viši harmonici (2 deo)

Nastavak prvog dela članka:
EES Kvalitet električne energije – viši harmonici (1)

Postavljanje filtera

U slučajevima kada navedena rešenja nisu dovoljna ili nemoguće ih je izvesti primenjuje se rešenje ugradnjom filtera. Postoje tri vrste filtera:

• Pasivni
• Aktivni
• Hibridni
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Pasivni filteri

Pasivni filteri se najčešće postavljaju paraleno potrošaču i sastoje se od kondenzatora sa pridodatom prigušnicom slika 5.4. Rezonantna frekvencija filtera se proračunava uvek da bude nešto ispod frekvencije najnižeg dominantnog harmonika. Time se obezbeđuje da filter pravilno radi i u slučaju oscilacija parametara kondenzatora zbog temperature i sl., a i da se izbegne da se antirezonantna učestanost približi učestanosti harmonika. Primena serijskih filtera se ređe primenjuje, a cilj im je da predstavljaju visoku impedansu za harmonike struje i na taj način blokiraju njihovo širenje u mrežu.

Primenjuju  se:

• U postrojenjima koja sadrže nelinearna opterećenja čije snage idu preko  200kVA,
• U postrojenjima koja traže popravku faktora snage,
• U postrojenjima gde se izobličenje napona mora smanjiti na dopuštene vrednosti,da bi se izbegao uticaj na osetljive prijemnike.

Slika 5.4. Pasivni filter

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Aktivni filteri

Aktivni filteri su u stvari energetski elektronski pretvarači, koji su tako programirani da vrše kompenzaciju viših harmonika.

Aktivni filteri kompenzuju više harmonike,proizvedene od strane nelinearnih prijemnika,tako što proizvode iste takve harmonike samo suprotnih faza. Sa takvim filterom obezbeđuje se „čista“ sinusoidna struja mreže, a često i faktor snage 1. Složenije konfiguracije omogućuju potpuno otklanjanje svih poremećaja, koji utiču na kvalitet električne energije.

Primenjuju  se postrojenjima koja sadrže nelinearna opterećenja čije snage su manje od  200kVA i u postrojenjima kod kojih bi usled velikog izobličenja struje došlo do preopterećenja.

Slika 5.5. Aktivni filter

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Slika 5.6. Talasni oblici struje opterećenja pre i posle filtriranja

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Popravka faktora snage

Najjednostavniji način da se ostvari kontrola viših harmonika i pritom popravi faktor snage je ugrađivanje kondenzatorskih baterija za kompenzaciju reaktivne energije.
Njihova rezonantna učestanost je često blizu učestanosti karakterističnih harmonika,pa dolazi do neželjenih neagativnih pojava.Dodavanjem redne impedanse u kolo kondenzatora negativne pojave se mogu otkloniti,šematski je to pokazano na slici 5.9. Ugradnjom kondenzatorskih baterija ostvaruje se značajna kontrola petog harmonika.

Slika 5.9. Kondenzatorska baterija sa pridodatim rednim impedansama

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Standardi i preporuke

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Standardi i preporuke u Francuskoj

U Francuskoj su prema preporuci Regulations Concerning the Installation of Power Convertors Taking into Account the Characteristics of the Supply Network, definisane sledeće granične vrednosti viših harmonika harmonijskog izobličenja, kada je samo jedan potrošač vezan za tačku priključenja na mrežu, i iznose:

• za parne harmonike 0,6% osnovnog harmonika napona,
• za neparne harmonike 1% osnovnog harmonika napona,
• ukupno harmonisko izobličenje napona u tački priključenja 1,6%.

Ove granice su izabrane tako da se osigura nivo od oko 5% THD napona u tački priključenja, da ne bude premašen kada su svi potrošači priključeni.

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Nemački standard  DIN 57160 (VDE 0160/11.81)

U Nemačkoj standard DIN 57160 (VDE 0160/11.81) određuje dozvoljene nazivne vrednosti uređaja koji generišu više harmonike, koje nisu veće od 1% vrednosti snage kratkog spoja. Pojedinačni nivoi harmonika, do 15-tog harmonika iznose 5% osnovnog harmonika napona,dozvoljeni nivo harmonika opada do 1% osnovnog harmonika napona za 100-ti harmonik, prema definisanoj krivoj liniji.

Ukupno harmonisko izobličenje napona u tački priključenja ne sme da pređe 10%.

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Standardi i preporuke u Švedskoj

Švedska, probleme viših harmonika opisuje u posebnoj preporuci i definiše zahteve kojima se ograničava priključenje potrošača u zavisnosti od mesta priključenja,vrste potrošača i ukupnog harmonijskog izobličenja.
U tabeli 1. su prikazane vrednosti ukupnog dozvoljenog harmonijskog izobličenja napona u zavisnosti od nazivnog napona napojne mreže.

Tabela 1. Ukupno dozvoljeno harmonijsko izobličenje u Švedskoj

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Standardi i preporuke u Australiji

Istorijski gledano, prvi kompletan standard koji razmatra probleme viših harmonika u distributivnim i prenosnim mrežama je izdat u Australiji (Standard AS 2279-1991)

Standard se sastoji iz četiri dela:

• prvi deo razmatra i definiše dozvoljene vrednosti viših harmonika prouzrokovanih priključenjem aparata za domaćinstvo i sličnih uređaja,
• drugi deo razmatra i definiše dozvoljene vrednosti viših harmonika prouzrokovanih priključenjem industrijskih postrojenja,
• treći i četvrti deo se odnose na dozvoljene fluktuacije napona prouzrokovane priključenjem aparata za domaćinstvo i sličnih uređaja i industrijskih postrojenja.

Prvi deo standarda se primenjuje na aparate za domaćinstvo i slične uređaje naznačene snage manje od 4,8 kVA priključene na distributivnu niskonaponsku mrežu nazivnog napona 240 V monofaznog sistema i 240/415 V trofaznog sistema. U ovom delu standarda se određuju:

• dozvoljene vrednosti viših harmonika struje koje mogu u distributivnu mrežu unositi pomenuti uređaji,
• referentna impedansa mreže,
• praktične metode merenja viših harmonika.

Za monofazne uređaje naznačenog napona 240 V, kao i za trofazne uređaje naznačenog napona 415 V, primenjuju se granične vrednosti harmonika struje I_h, i napona V_h prema tabelama 2 i 3.

Tabela 2. Granične vrednosti harmonika struje prema Australijskom standardu AS 2279-1991

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Tabela 3. Granične vrednosti harmonika napona prema Australijskom standardu AS 2279-1991

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U drugom delu standarda date su maksimalno dozvoljene vrednosti viših harmonika koje u distributivnu mrežu unosi industrijska oprema napajana sa srednjeg i visokog napona,naznačene snage veće od 4,8 kVA. Kako je pomenuta oprema raznovrsna, izvršena je njena podela u tri velike grupe:

• Prvu grupu čine uređaji koji se mogu priključiti bez posebne dozvole na distributivnu mrežu, a čija naznačena snaga je manja od 0,3% snage trofaznog kratkog spoja u tački priključenja.
  • Pri tome je nazivna snaga uređaja manja od 75 kVA, za priključenje na sekundarnu mrežu, odnosno 500 kVA za primarnu distributivnu mrežu (napon mreže od 415 V do 33 kV). Pri tome snaga kratkog spoja mora biti najmanje 5 MVA za sekundarnu mrežu (415/240 V), odnosno 50 MVA za primarnu distributivnu mrežu (6,6; 11 i 24 kV).
  • U slučaju priključenja više manjih pretvarača suma njihovih snaga ne sme da pređe granicu od 75 kVA;
  • Pri monofaznom priključenju naznačena snaga pretvarača nije veća od 5 kVA pri naponu 240 V, odnosno 7,5 kVA pri naponu 415 V.
• Druga grupa potrošača obuhvata uređaje koji se mogu priključiti na distributivnu mrežu ako postojeće ukupno harmonijsko izobličenje u tački priključenja nije veće od 75% vrednosti harmonika napona pre priključenja.
• U treću grupu spadaju uređaji velikih snaga i za njih su potrebna posebna merenja i studije.

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Standardi i preporuke međunarodne elektrotehničke komisije (IEC)

Problemom viših harmonika se bavi više radnih grupa Međunarodne elektrotehničke komisije (IEC). Prvi standard se pojavio 1982. godine, (IEC 555) koji se sastoji iz tri dela: IEC 555-1 Definicije, IEC 555-2 Harmonici, IEC 555-3 Fluktuacije napona. Ovaj standard je preveden i primenjuje se u Srbiji i Crnoj Gori od 1989-godine, (JUS N.A6.101, JUS N.A6.102, JUS N.A6.103).

Dalji rad IEC komiteta TC 77 rezultovao je nizom standarda kojima se ograničavaju struje i naponi viših harmonika na vrednosti za koje se smatra da električna mreža može da ih toleriše. Tu se posebno izdvajaju standardi iz grupe IEC 61000, u kojima je obrađena problematika viših harmonika (osnovne definicije,merenja, proračuni i dozvoljene granične vrednosti).

U standardu IEC 61000-3-6 , definišu se osnovni zahtevi koje treba da ispune nelinearni potrošači da bi se priključili na distributivnu mrežu. Granične vrednosti viših harmonika su tako određene da se održi zadovoljavajući kvalitet napona i to kako u tački priključenja nelinearnog potrošača na distributivnu mrežu tako i prema ostalim potrošačima.

Tabela 4. Granične vrednosti harmonika napona na nivou elektromagnetne kompatibilnosti prema standardu IEC 61000-2-2

Na osnovu ove procedure može se proceniti da li će amplitude unetih viših harmonika u distributivnu mrežu zadovoljiti planirani nivo, odnosno nivo elektromagnetne kompatibilnosti. Ukoliko potrošači zadovolje navedene granične vrednosti sadržaja viših harmonika, dozvoljava se priključenje, a u protivnom se priključenje uslovljava odgovarajućim metodom za eliminaciju viših harmonika.

Takođe, ovim standardom se definiše da za pojavu viših harmonika u havarijskim radnim režimima odgovornost snosi isporučilac električne energije a ne potrošač. Za priključenje malih potrošača koji ne unose značajna harmonijska izobličenja struje i napona ne mora se tražiti posebna dozvola. Priključenja ovih potrošača na niskom naponu su regulisana standardima IEC 61000-3-2 i IEC 61000-3-4.

Zaključak

Otvaranjem tržišta, električna energija postaje roba kao i svaki drugi proizvod te mora zadovoljavati zadate kriterijume kvaliteta. U prenosnoj mreži probleme predstavljaju elektrolučne peći,vetroelektrane, i železnica, dok su u distributivnoj mreži najveći problem uređaji koji se zasnivaju na energetskoj elektronici.

Ograničavanje viših harmonika u distributivnim mrežama pomoću odgovarajućih standarda i preporuka neophodno je iz više razloga:

• da se ograniči nivo izobličenja talasnih oblika struje i napona na vrednosti koje sistem i njegovi elementi mogu da tolerišu i time omoguće kvalitetnu isporuku električne energije potrošačima,
• da ne utiču na dalje širenje upotrebe energetskih pretvarača i drugih uređaja koji unose nelinearnost u distributivnu mrežu,
• da se ograniči ometanje drugih uređaja i sistema od strane distributivne mreže (telefonske mreže i sl.)

Iz pregleda nacionalnih standarda i preporuka se vidi da većina njih određuje granične vrednosti ukupnog harmonijskog izobličenja THD, koje se razlikuju na pojedinim naponskim nivoima. U većini zemalja se ovaj faktor usvaja da bude za niski napon THD <5%, za srednji napon THD je između 3 i 5%, a za visoki 1-1,5%.

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AUTOR STRUČNOG TEKSTA:

Dragan Simović

Seminarski rad iz predmeta: Eksploatacija EES, tema: Kvalitet električne energije – viši harmonici
Visoka Škola Tehničkih Strukovnih Studija Čačak
Specijalističke Strukovne Studije Elektrotehnike i Računarstva | Modul Studijskog Programa: Elektroenergetika

Maintenance Of Meduim Voltage Circuit Breakers

Medium-voltage circuit breakers rated between 1 and 72 kV may be assembled into metal-enclosed switchgear line ups for indoor use, or may be individual components installed outdoors in a substation. Air-break circuit breakers replaced oil-filled units for indoor applications, but are now themselves being replaced by vacuum circuit breakers (up to about 35 kV).

Medium voltage circuit breakers which operate in the range of 600 to 15,000 volts should be inspected and maintained annually or after every 2,000 operations, whichever comes first.

The above maintenance schedule is recommended by the applicable standards to achieve required performance from the breakers.
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Safety Practices

Maintenance procedures include the safety practices indicated in the ROMSS (Reclamation Operation & Maintenance Safety Standards) and following points that require special attention.

• Be sure the circuit breaker and its mechanism are disconnected from all electric power, both high voltage and control voltage, before it is inspected or repaired.
• Exhaust the pressure from air receiver of any compressed air circuit breaker before it is inspected or re­paired.
• After the circuit breaker has been disconnected from the electrical power, attach the grounding leads properly before touching any of the circuit breaker parts.
• Do no lay tools down on the equipment while working on it as they may be forgotten when the equipment is placed back in service.
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Maintenance Procedures For Medium Voltage Air Circuit Breakers

The following suggestions are for use in conjunction with manufacturer’s instruction books for the maintenance of medium voltage air circuit breakers:

1. Clean the insulating parts including the bushings.
2. Check the alignment and condition of movable and stationary contacts and adjust them per the manufacturer’s data.
3. See that bolts, nuts, washers, cotter pins, and all terminal connections are in place and tight.
4. Check arc chutes for damage and replace damaged parts.
5. Clean and lubricate the operating mechanism and adjust it as described in the instruction book. If the operat­ing mechanism cannot be brought into specified tolerances, it will usually indicate excessive wear and the need for a complete overhaul.
6. Check, after servicing, circuit breaker to verify that contacts move to the fully opened and fully closed positions, that there is an absence of friction or binding, and that electrical operation is functional.
   .

Maintenance Procedures For Medium Voltage Oil Circuit Breakers

The following suggestions are for use in conjunction with the manufacturer’s instruction books for the maintenance of medium-voltage oil circuit breakers:

1. Check the condition, alignment, and adjustment of the contacts.
2. Thoroughly clean the tank and other parts which have been in con­ tact with the oil.
3. Test the dielectric strength of the oil and filter or replace the oil if the dielectric strength is less than 22 kV. The oil should be filtered or replaced whenever a visual inspection shows an excessive amount of carbon, even if the dielectric strength is satisfactory.
4. Check breaker and operating mechanisms for loose hardware and missing or broken cotter pins, retain­ ing rings, etc.
5. Adjust breaker as indicated in instruction book.
6. Clean and lubricate operating mechanism.
7. Before replacing the tank, check to see there is no friction or binding that would hinder the breaker’s operation. Also check the electrical operation. Avoid operating the breaker any more than necessary without oil in the tank as it is designed to operate in oil and mechanical damage can result from excessive operation without it.
8. When replacing the tank and refilling it with oil, be sure the gaskets are undamaged and all nuts and valves are tightened properly to prevent leak­ age.
   .

Maintenance Procedures For Medium Voltage Vacuum Circuit Breakers

Direct inspection of the primary contacts is not possible as they are enclosed in vacuum containers. The operating mechanisms are similar to the breakers discussed earlier and may be maintained in the same manner. The following two maintenance checks are suggested for the primary contacts:

1. Measuring the change in external shaft position after a period of use can indicate extent of contact erosion. Consult the manufacturer’s instruction book.
2. Condition of the vacuum can be checked by a hipot test. Consult the manufacturer’s instruction book.
   .

SOURCE: MAINTENANCE OF POWER CIRCUIT BREAKERS by HYDROELECTRIC RESEARCH AND TECHNICAL SERVICES GROUP

EES Kvalitet električne energije - viši harmonici (prvi deo)

Prisustvo velikog broja nelinearnih potrošača u distributivnim mrežama dovodi do niza negativnih efekata koji se odražavaju kako na samu mrežu tako i na ostale priključene potrošače.

Zajednički interes potrošača i proizvođača električne energije je poslednjih godina doveo u žižu interesovanja probleme vezane za kvalitet električne energije, odnosno sadržaj harmonika u distributivnoj mreži i druge aspekte kvaliteta električne energije (neprekidnost napajanja, prisustvo kratkotrajnih fluktuacija i distorzija,…).

Danas je u svetu pred proizvođače i projektante uređaja energetske elektronike postavljen čitav niz standarda i preporuka iz oblasti kvaliteta električne energije. Tradicionalno se smatralo da je kvalitet električne energije u stvari pouzdanost,odnosno nepostojanje trajnih prekida u snabdevanju električnom energijom, dok moderno shvatanje kvaliteta električne energije podrazumeva i sigurno (neprekidno) napajanje i fizički kvalitet napona. Problemi neprekidnosti napajanja se uglavnom rešavaju u toku postupka planiranja i izgradnje mreže, dok je problem fizičkog kvaliteta napona usko vezan za eksploataciju. Dominantan uticaj na fizički kvalitet napona imaju nelinearni potrošači (uređaji energetske elektronike, zasićene električne mašine,elektrolučne peći, itd…),tranzijentne pojave usled komutacija u sistemu (rad prekidača),rad elektroenergetskog sistema na granicama mogućnosti, itd…

Narušavanje kvaliteta električne energije podrazumeva narušavanje osnovnih parametara napona u ustaljenim ili prelaznim režimima i deformaciju talasnih oblika. Osnovni parametri napona su njegova efektivna vrednost, frekvencija i simetrija faznih napona.Dalje će biti razmatrani standardi vezani za sadržaj viših harmonika kako napojnog napona tako i struje koju potrošač uzima, dok drugi aspekti kvaliteta električne energije se neće razmatrati.

Viši harmonici

Napon viših harmonika je sinusni napon, čija je frekvencija celobrojni umnožak frekvencije osnovnog harmonika.Viši harmonici su nepoželjni u mrežama, jer se zbrajaju na osnovni talas i izobličuju ga, što uzrokuje problem u napajanju osetljivih potrošača, npr. medicinske opreme,koja zahteva čisti sinusni napon.

Slika 2.Talasni oblici napona prvog,petog i sedmog harmonika

Dopuštene vrednosti viših harmonika (h od 2 do 40) tablično se prikazuju, i to:

• pojedinačno, njihovim amplitudama (U_h), svedenim na amplitudu osnovnog harmonika  (U₁),
• zajednički, pomoću ukupnog sadržaja viših harmonika: THD (eng. Total Harmonic Distortion –    ukupno harmonijsko izobličenje), koje se izračunava kao:
  .
  

Tokom svakog desetminutnog intervala vrednost THD-a mora biti < 8% vrednosti prvog harmonika, dok vrednosti pojedinih harmonika mogu imati vrednosti najčešće u pojasu od 0,5% (npr. od 6., do 24. harmonika) do 6% (npr. za “poznati” 5. harmonik) od vrednosti prvog harmonika.Više harmonike u mrežnom naponu najčešće proizvode viši harmonici struja nelinearnih opterećenja potrošača, koji su priključeni na različitim nivoima distributivne mreže. Ti viši harmonici struje opterećenja stvaraju na impedansama unutar distributivne mreže odgovarajuće više harmonike napojnog napona. S druge strane, sve veća primena pretvarača frekvencije i sličnih upravljačkih uređaja utiče na povećanje vrednosti međuharmonika, čije se dopuštene vrednosti u okviru norme EN 50160 još razmatraju.

U pojedinim situacijama i međuharmonici malih intenziteta izazivaju treperenje (flikere) ili smetnje u sistemu mrežnog tonfrekventnog upravljanja.

Merenje ukupnog harmonijskog izobličenja napona

Za izračunavanje  THD U   koriste se izmerene (RMS) vrednosti svakog od prvih 40 harmonika (Un) i vrednost nazivnog napona (osnovni harmonik), koja prema normi EN 50160 iznosi npr.: U1 = 220 V, a prema jednačini:

Pomnoženo sa 100%, THD U % ne sme biti veće od 8% vrednosti nazivnog napona. Ta jednačina u skladu je sa normom EN 61000-4-7.

Izračunavanje ukupnoga harmonijskog izobličenja napona i struje

Za izračunavanje THD U i THD I,  primenjuju se sledeće jednačine:

Pri čemu su:
U_rms – efektivna vrednost (RMS – Root Mean Square) ukupnog napona
U₁ – efektivna (RMS) vrednost napona osnovnog harmonika
I_rms – efektivna vrednost ukupnog signala struje
I₁ – RMS vrednost struje osnovnog harmonika (nazivna vrednost signala na 50 Hz).

Izvori viših harmonika

Izvori viših harmonica su:

• Prekidačke napojne jedinice
• Elektronske prigušnice za fluo cevi
• Regulisani elektromotorni pogoni
• Besprekidna napajanja
• Energetski ispravljači i pretvarači
• Transformatori sa nelinearnim magnećenjem
• Elektrolučne peći
• Indukcione peći
• Aparati za elektrolučno zavarivanje

Slika 3.1 Šema trofaznog ispravljača | Slika 3.2. Talasni oblik struje trofaznog ispravljača

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Slika 3.5. Talasni oblici struje: a) magnećenja transformatora,b) hladnjaka zamrzivača,c) klima uređaja,d) jednofaznog pretvarača sa sklopnim načinom rada,e) fluorescentne cevi sa elektromagnetnom prigušnicom,d) fluorescentne cevi sa elektronskom prigušnicom

Problemi zbog viših harmonika

Problemi koji u elektroenergetskom sistemu nastaju zbog prisustva viših harmonika su brojni i ovde će biti navedeni samo neki, kao što su:

Manja iskoristivost snage. Mrežni kablovi su dimenzionisani i osigurani na osnovu struje koju mogu sigurno isporučiti. Pošto mali faktor snage povećava prividnu struju iz izvora, iznos korisne snage koju može povući kolo je smanjen zbog toplotnih ograničenja.
Enormno smanjenje raspoložive snage izazvano je ili faznim pomakom ili distorzijom.

Troškovi distribucije. Ako postoji mnoštvo opterećenja sa malim faktorom snage, postavljaju se zahtevi za dodatnim proizvodnim i distributivnim kapacitetima. Troškovi, rastu proporcionalno sa inverznom vrednošću faktora snage. Gubici u disipativnim elementima (žice i namotaji transformatora) proporcionalni su kvadratu prividne struje pa troškovi za obezbeđenje ove disipirane snage su takođe u inverznoj vezi sa faktorom snage. Brojila električne energije registrovaće samo aktivnu snagu pa korisnici ne plaćaju reaktivnu snagu.

Distorzija napona. Impedanse realnih izvora su konačne. Kablovi su sve tanji prema krajnjim potrošačima električne energije. Mali preseci provodnika u uređajima i velika strujna distorzija utiču na oblik napona i on postaje nesinusoidan.Distorzija napona izaziva probleme u radu napojnih jedinica i drugih obližnjih uređaja spojenih na isti izvor.

Trofazni sistemi. Nesimetrično opterećenje izaziva neželjene struje u neutralnom provodniku. Ali, čak i kod potpuno simetrčnog opterećenja koje generiše više harmonike, harmonijski sadržaj će se pojaviti u neutralnom provodniku ( to su tzv. harmonici trećeg reda, 3-ći, 6-ti, 9-ti itd.).
Prethodno nabrojani negativni efekti koje izaziva distorzija mrežne struje i viši harmonici, doveli su do potrebe za postavljanjem ograničenja na strujne harmonike koje u mreži izazivaju priključeni uređaji.

Metode za neutralisanje viših harmonika

Da bi se harmonijski problem smanjio ili eliminisao postoji nekoliko osnovnim rešenja:

• smanjenje intenziteta harmonijskih struja
• postavljanje filtera
• popravka faktora snage

Metode smanjenja intenziteta harmonijskih struja

Metode smanjenja intenziteta harmonijskih struja obično podrazumevaju menjanje načina rada pogona, koji generišu harmonike. Takav pristup je teško praktično izvesti, jer to može da utiče na kompletan proizvodni proces, odnosno moguće je jedino u fazi projektovanja.
Neka od rešenja koja se koriste pri ograničavanju viših harmonika u fazi projektovanja su:

• Izmeštanje nelinearnih prijemnika što dalje od osetljive opreme.
  Slika 5. Izmeštanje nelinearnih prijemnika
• Grupisanje nelinearnih prijemnika,koji se priključuju na odvojene sabirnice.
  
  Slika 5.1. Priključenje više nelinearnih prijemnika
  .
• Instaliranje više transformatora,jedni napajaju nelinearne prijemnike,dok drugi napajaju linearne prijemnike.
  
  Slika 5.2. Posebni transformatori za posebne vrste prijemnika
  .
• Odgovarajućim sprezanjem transformatora mogu se ograničiti viši harmonici. Sprega namotaja u trougao dovodi do blokiranja daljeg toka svih harmonika, koji su umnozak od 3. Unošenjem faznog pomeraja od 30 stepeni, sprezanjem sekundara transformatora u zvezdu i u trougao, dobija se efekat 12-pulsnog ispravljača, odnosno eliminišu se 5-ti i 7-mi harmonik.
  
  Slika 5.3. Različito sprezanje namotaja utiče na eliminisanje pojedinih harmonika

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Uskoro u nastavku stručnog teksta: EES Kvalitet električne energije – viši harmonici (2):

• Postavljanje filtera (pasivni, aktivni i hibridni)
• Popravka faktora snage
• Standardi i preporuke (u Francuskoj, Švedskoj, Australiji)
• Standardi i preporuke međunarodne elektrotehničke komisije (IEC)

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AUTOR STRUČNOG TEKSTA:

Dragan Simović

Seminarski rad iz predmeta: Eksploatacija EES, tema: Kvalitet električne energije – viši harmonici
Visoka Škola Tehničkih Strukovnih Studija Čačak
Specijalističke Strukovne Studije Elektrotehnike i Računarstva | Modul Studijskog Programa: Elektroenergetika

International Standard - IEC 61850

The traditional approach to substation integration used standardized RTU protocols that were designed to provide protocol efficiency for operation over bandwidth limited serial links.

While such limitations remain for many applications, substation hardened equipment implementing modern networking standards like Ethernet now provide a cost effective means of enabling high speed communications within the substation.

To truly take advantage of this technology and dramatically lower the total cost of ownership of substation automation systems, a new approach to substation integration that goes beyond a simple RTU protocol is needed.

The recent international standard IEC 61850 proposes a unified solution of the communication aspect of substation automation. However, the standard itself is not easily understood by users other than domain experts. We present our understanding of the IEC 61850 standard as well as the design and implementation of our simulation tool in this report. Also, we give suggestions on the implementation of this standard based on our experience and lessons in the development of our simulation.

1. Introduction

Today, power substations are mostly managed by substation automation systems. These systems employ computers and domain specific applications to optimize the management of substation equipment and to enhance operation and maintenance efficiencies with minimal human intervention [8].

Once upon a time, substation automation systems utilized simple, straightforward and highly specialized communication protocols [7].    These protocols concerned less about the semantics of the exchanged data, data types of which were relatively primitive. Equipment was dumb and systems were simple. However, today’s substation automation systems can no longer enjoy such simplicity because of their growing complexity — equipment becomes more intelligent and most of those simple old systems have been gradually replaced by open systems, which embrace the advantage of emerging technology like relational database systems, multi-task operating systems and support for state-of-the-art graphical display technology.

Besides, devices from different manufacturers used different substation automation protocols [9, 3, 12], disabling them to talk to each other. Utilities have been paying enormous money and time to configure these devices to work together in a single substation. Today most utilities and device manufacturers have recognized the need for a unified international standard to support seamless cooperation among products from different vendors.

The IEC 61850 international standard, drafted by substation automation domain experts from 22 countries, seeks to tackle the aforementioned situation. This standard takes advantage of a comprehensive object-oriented data model and the Ethernet technology, bringing in great reduction of the configuration and maintenance cost. Unlike its predecessor, the Utility Communication Architecture protocol 2.0 (UCA 2.0) [12], the IEC 61850 standard is designed to be capable for domains besides substation automation. To make the new protocol less domain dependent, the standard committee endeavored to emphasize on the data semantics, carving out most of the communication details. This effort, however, could result in difficulties in understanding the standard.

In this research project, we aim to get a clear understanding of the IEC 61850 standard and simulate the protocol based on J-Sim [11]. Our ultimate goal is to investigate the security aspect about the IEC 61850 standard.

2    The IEC 61850 standard

The first release of the IEC 61850 consists of a set of documents of over 1,400 pages. These documents are divided into 10 parts, as listed in Table 1. Part 1 to Part 3 give some general ideas about the standard. Part 4 defines the project and management requirements in an IEC 61850 enabled substation. Part 5 specifies the required parameters for physical implementation. Part 6 defines an XML based language for IED configuration, presenting a formal view of the concepts in the standard. Part 7 elaborates on the logical concepts, which is further divided into four subparts (listed in Table 2). Part 8 talks about how to map the internal objects to the presentation layer and to the Ethernet link layer. Part 9 defines the mapping from sampled measurement value (SMV) to point-to-point Ethernet.

The last part gives instructions on conformance testing. Since Part 7 defines the core concepts of the IEC 61850 standard, we will focus on this part in this report.

The IEC 61850 standard is not easy to understand for people other than experts in the substation automation domain due to the complexity of the documents and the assumed domain-specific knowledge. Introductory documents on the standard abound [13, 4, 7, 5, 8, 2], but most of them are in the view of substation automation domain experts. Kostic et al. explained the difficulties they had in understanding the IEC 61850 standard [7].

In this section, we provide another experience of understanding this standard, trying to explain the major concepts of the IEC 61850 standard.

2.1 Challenges

Understanding the IEC 61850 standard proposes the following challenges for a outsider of the substation automation domain:

1. As a substation automation standard proposed by a group of domain experts, the IEC 61850 protocol assumes quite an amount of domain-specific knowledge, which is hardly accessible by engineers and researchers out of the substation automation domain. To make things worse, the terms used in the standard is to some extent different from those commonly used in software engineering, bringing some difficulties for software engineers in reading the standard.
2. The entire standard, except Part 6, is described in natural language with tables and pictures, which is known to be ambiguous and lack of preciseness. This situation is problematic because the IEC 61850 concepts are defined by more than 150 mutually relevant tables distributed over more than 1,000 pages. A formal presentation of all these concepts would be appreciated.
3. The experts proposing this protocol come from 22 different countries and are divided into 10 working groups, each responsible to one part of the standard. Due to the different backgrounds and the informal presentation style of the standard, the standard contains a considerable number of inconsistencies. Such inconsistencies are more obvious for different parts of the standard, e.g. the data model described in Part 6 is clearly different from that described in Part 7.
4. The standard committee made a great effort to describe the protocol in an object-oriented manner but the result is not so object-oriented. For example, the ACSI services are grouped by different classes, but reference to the callee object is not defined as a mandatory argument of the service function.
5. The standard is designed to be implementation independent but this is not always true. For example, the data attribute TimeAccuracy in Part 7-2 Table 8 is defined as CODED ENUM, while what it virtually represents is a 5-bit unsigned integer; the frequent use of PACKED LIST (i.e. “bit fields” in the C language) also brings implementation details to interface design.
6. Things are mixed up in the documents. Mandatory components and optional components are mixed in the standard, and domain independent concepts are mixed up with domain specific concepts. Even though the optional components and mandatory ones are marked with “O” and “M” alternatively, it would be a tough task to refine a model consisting only the mandatory components due to the implicit dependences between attributes in different tables and the conditional inclusion of some attributes. In fact, there are 29 common data classes and 89 compatible logical nodes defined in the standard, the relationship among which is unclear.
   .

2.2    Intelligent electronic device

In the past, utility communication standards usually assumed some domain-specific background of the readers. Consequently, they contained a lot of implicit domain knowledge, which is hardly accessible to outsiders (e.g. software engineers) [7]. The IEC 61850 standard does not escape from this category. To help understanding the logical concepts of IEC 61850, we would like to lay a basic idea of intelligent electronic devices (IED), the essential physical object hosting all the logical objects.

Basically, the term intelligent electronic device refers to microprocessor-based controllers of power system equipment, which is capable to receive or send data/control from or to an external source [8]. An IED is usually equipped with one or more microprocessors, memory, possibly a hard disk and a collection of communication interfaces (e.g. USB ports, serial ports, Ethernet interfaces), which implies that it is essentially a computer as those for everyday use.

However, IEDs may contain some specific digital logics for domain-specific processing.
IEDs can be classified by their functions. Common types of IEDs include relay devices, circuit breaker controllers, recloser controllers, voltage regulators etc.. It should be noted that one IED can perform more than one functions, taking advantage of its general-purpose microprocessors. An IED may have an operating system like Linux running in it.

2.3 Substation architecture

A typical substation architecture is shown in Figure 1. The substation network is connected to the outside wide area network via a secure gateway. Outside remote operators and control centers can use the abstract communication service interface (ACSI) defined in Part 7-2 to query and control devices in the substation. There is one or more substation buses connecting all the IEDs inside a substation. A substation bus is realized as a medium bandwidth Ethernet network, which carries all ACSI requests/responses and generic substation events messages (GSE, including GOOSE and GSSE).

There is another kind of bus called process bus for communication inside each bay. A process bus connects the IEDs to the traditional dumb devices (merge units, etc.) and is realized as a high bandwidth Ethernet network. A substation usually has only one global substation bus but multiple process buses, one for each bay.

Figure 1: Substation architecture

ACSI requests/responses, GSE messges and sampled analog values are the three major kinds of data active in the substation network. Since we are less interested in communication on the process buses (like sampled value multicasting), we focus on the activities on the substation bus in this report, especially the ACSI activities.

Interactions inside a substation automation system mainly fall into three categories: data gathering/setting, data monitoring/reporting and event logging.

The former two kinds of interactions are the most important — in the IEC 61850 standard all inquiries and control activities towards physical devices are modeled as getting or setting the values of the corresponding data attributes, while data monitoring/reporting provides an efficient way to track the system status, so that control commands can be issued in a timely manner.

To realize the above kinds of interaction, the IEC 61850 standard defines a relatively complicated communication structure, as is shown in Figure 2.

Figure 2: The communication profiles

Five kinds of communication profiles are defined in the standard: the abstract communication service interface profile (ACSI), the generic object oriented substation event profile (GOOSE), the generic substation status event profile (GSSE), the sampled measured value multicast profile (SMV), and the time synchronization profile. ACSI services enable client-server style interaction between applications and servers.

GOOSE provides a fast way of data exchange on the substation bus and GSSE provides an express way of substation level status exchange. Sample measured value multicast provides an effective way to exchange data on a process bus.
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2.4 Abstract communication service interface

ACSI is the primary interface in the IEC 61850 standard not only because it is the interface via which applications talk with servers, but also in the sense that the ACSI communication channel is an important part of a logical connection between two logical nodes. ACSI defines the semantics of the data exchanged between applications and servers, thus it becomes the major part of the IEC 61850 standard.

The standard committee adopt an object-oriented approach in the design of ACSI, which includes a hierarchical and comprehensive data model and a set of available services for each class in this data model. Although the data model is usually described outside the scope of the ACSI, it is actually part of it. The benefits of using an object-oriented utility communication interface are two fold. On the one hand, objects (e.g. registers) can be referenced in an intuitive way (e.g. “Relay0/MMXU0.voltage”) instead of by the traditional physical address (like Reg#02432). On the other hand, software engineers can build more reliable applications using such service interface.

In the following two sections, we present a brief description on these two ACSI components.
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2.5    Data model

The hierarchical data model defined in the IEC 61850 is depicted in Figure 3 and Figure 4.
Server is the topmost component in this hierarchy. It serves as the joint point of physical devices and logical objects. Theoretically one IED may host one or more server instances, but in practice usually only one server instance runs in an IED. A server instance is basically a program running in an IED, which shares the same meaning with other servers like FTP server etc.. Each server has one or more access points, which are the logical representation of a NIC. When a client is to access data or service of the server, it should connect to an access point of this server and establish a valid association.

Each server hosts several files or logical devices. Clients can manipulate files in the server like talking to a FTP server, which is usually used as a means to upload/update the configuration file of an IED. A logical device is the logical correspondence of a physical device. It is basically a group of logical nodes performing similar functions.
Functions supported by an IED are conceptually represented by a collection of primitive, atomic functional building blocks called logical nodes.

The IEC 61850 standard predefines a collection of template logical nodes (i.e. compatible logical nodes) in Part 7-4. Besides the regular logical nodes for functions, the standard also requires every logical device have two specific logical nodes: Logical Node Zero (LN0) and LPHD, which correspond to the logical device and the physical device, alternatively. Besides holding status information of the logical device, LN0 also provides additional functions like setting-group control, GSE control, sampled value control etc..

In the IEC 61850 standard, the entire substation system is modeled as a distributed system consisting of a collection of interacting logical nodes, which are logically connected by logical connections. It should be noted that the term logical connection refers to the logical concept of the connections between two logical nodes, which can be direct or indirect or even a combination of many different kinds of communication channels. In fact, the connection of two logical nodes is usually both indirect and a combination of TCP, UDP and direct Ethernet connections. We will explain logical connections in Section 2.9 (next article).

Data exchanged between logical nodes are modeled as data objects. A logical node usually contains several data objects. Each data object is an instance of the DATA class and has a common data class type.

Figure 3: Hierarchy of the IEC 61850 data model

Similar to the concept of objects in most object-oriented programming languages, a data object consists of many data attributes, which are instances of data attributes of the corresponding common data class. Data attributes are typed and restricted by some functional constraints. Instead of grouping data attributes by data objects, functional constraints provide a way to organize all the data attributes in a logical node by functions. Types of data attributes can be either basic or composite.

Basic types are primitive types in many programming languages, whereas composite types are composition of a collection of primitive types or composite types.
In the IEC 61850 standard, data attributes are at least as important as, if not more than, data objects for two reasons.

Figure 4: The data model of the IEC 61850

Firstly, data objects are just logical collections of the contained data attributes while (primitive) data attributes are the de facto logical correspondence to the physical entities (memory units, registers, communication ports, etc.); secondly, the purpose of data objects is for the convenience of managing and exchanging values of a group of data attributes sharing the same function.

Despite data objects, the IEC 61850 standard provides the concept of data set as another ways to manage and exchange a group of data attributes. Members of a data set can be data objects or data attributes. The concept of data set is somewhat similar to the concept of view in the area of database management systems.

In the IEC 61850 standard, most services involve data sets. Members in a data set unnecessarily come from the same logical node or the same data object, thus providing high flexibility of data management. Data sets are categorized into permanent ones and temporary ones.

Permanent data sets are hosted by logical nodes and will not be automatically deleted unless on the owners’ explicit requests; temporary data sets are exclusively hosted by the association having created them and will be automatically deleted when the association ends.

To be continued soon in next article: IEC 61850 in details (2)

SOURCE:

• Understanding and Simulating the IEC 61850 Standard by Yingyi Liang & Roy H. Campbell, Department of Computer Science University of Illinois at Urbana-Champaign

Maintenance Of Low Voltage Circuit Breakers

The deterioration of low voltage circuit breaker is normal and  this process begins as soon as the circuit breaker is installed. If  deterioration is not checked, it can cause failures and malfunctions. The purpose of an electrical preventive maintenance and testing program should be to recognize these factors and provide means for correcting them.

A good organized maintenance program can minimize accidents, reduce unplanned shutdowns and lenghten the mean time between failures of electrical equipment.

Benefits of good electrical equipment maintenance can be reduced cost of process shutdown (caused by circuit breaker failure), reduced cost of repairs, reduced downtime of equipment, improved safety of personnel and property.

Frequency Of Maintenance

Low-voltage circuit breakers operating at 600 volts alternating current and below should be inspected and maintained very 1 to 3 years, depending on their service and operating conditions. Conditions that make frequency maintenance and inspection necessary are:

1. High humidity and high ambient temperature.
2. Dusty or dirty atmosphere.
3. Corrosive atmosphere.
4. Frequent switching operations.
5. Frequent fault operations.
6. Older equipment.

A breaker should be inspected and maintained if necessary whenever it has interrupted current at or near its rated capacity.

Maintenance Procedures

Manufacturer’s instructions for each cir­ cuit breaker should be carefully read and followed. The following are general pro­ cedures that should be followed in the maintenance of low-voltage air circuit breakers:

1. An initial check of the breaker should be made in the TEST position prior to withdrawing it from to enclo­sure.
2. Insulating parts, including bushings, should be wiped clean of dust and smoke.
3. The alignment and condition of the movable and stationary contacts should be checked and adjusted ac­cording to the manufacturer’s instruction book.
4. Check arc chutes and replaces any damaged parts.
5. Inspect breaker operating mechanism for loose hardware and missing or broken cotter pins, etc. Examine cam, latch, and roller surfaces for damage or wear.
6. Clean and relubricate operating mechanism with a light machine oil (SAE-20 or 30) for pins and bearings and with a nonhardening grease for the wearing surfaces of cams, rollers, etc.
7. Set breaker operating mechanism adjustments as described in the manufacturer’s instruction book. If these adjustments cannot be made within the specified tolerances, it may indicate excessive wear and the need for a complete overhaul.
8. Replace contacts if badly worn or burned and check control device for freedom of operation.
9. Inspect wiring connections for tightness.
10. Check after servicing circuit breaker to verify the contacts move to the fully opened and fully closed positions, that there is an absence of friction or binding, and that electrical operation is functional.

Much of the essence of effective electrical equipment preventive maintenance can be sumarrized by four rules:

• Keep it DRY
• Keep it CLEAN
• Keep it COOL
• Keep it TIGHT

SOURCES:

• MAINTENANCE OF POWER CIRCUIT BREAKERS by HYDROELECTRIC RESEARCH AND TECHNICAL SERVICES GROUP
• ELECTRICAL POWER EQUIPMENT MAINTENANCE AND TESTING – By Paul Gill

Maintenance Of Molded Case Circuit Breakers (MCCB)

The maintenance of circuit breakers deserves special consideration because of their importance for routine switching and for protection of other equipment.

Electric transmission system breakups and equip­ment destruction can occur if a circuit breaker fails to operate because of a lack of preventive maintenance.

The need for maintenance of circuit breakers is often not obvious as circuit breakers may remain idle, either open or closed, for long periods of time. Breakers that remain idle for 6 months or more should be made to open and close several times in succession to verify proper operation and remove any accumulation of dust or foreign material on moving parts and contacts.

Frequency Of Maintenance

Molded case circuit breakers are designed to require little or no routine maintenance throughout their normal life­ time. Therefore, the need for preventive maintenance will vary depending on operating conditions. As an accumulation of dust on the latch surfaces may affect the operation of the breaker, molded case circuit breakers should be exercised at least once per year.

Routine trip testing should be performed every 3 to 5 years.

Routine Maintenance Tests

Routine maintenance tests enable personnel to determine if breakers are able to perform their basic circuit protective functions. The following tests may be performed during routine maintenance and are aimed at assuring that the breakers are functionally operable. The following tests are to be made only on breakers and equipment that are deenergized.

Insulation Resistance Test

A megohmmeter may be used to make tests between phases of opposite polarity and from current-carrying parts of the circuit breaker to ground. A test should also be made between the line and load terminals with the breaker in the open position. Load and line conductors should be dis­ connected from the breaker under insulation resistance tests to prevent test mesurements from also showing resistance of the attached circuit.

Resistance values below 1 megohm are considered unsafe and the breaker should be inspected for pos­ sible contamination on its surfaces.

Milivolt Drop Test

A millivolt drop test can disclose several abnor­ mal conditions inside a breaker such as eroded contacts, contaminated contacts, or loose internal connec­ tions. The millivolt drop test should be made at a nominal direct-current volt­ age at 50 amperes or 100 amperes for large breakers, and at or below rating for smaller breakers. The millivolt drop is compared against manufacturer’s data for the breaker being tested.

Connections Test

The connections to the circuit breaker should be inspected to determine that a good joint is present and that overheating is not occurring. If overheating is indi­ cated by discoloration or signs of arcing, the connections should be re­ moved and the connecting surfaces cleaned.

Overload tripping test

The proper action of the overload tripping components of the circuit breaker can be verified by applying 300 percent of the breaker rated continuous current to each pole. The significant part of this test is the automatic opening of the circuit breaker and not tripping times as these can be greatly affected by ambient conditions and test condi­ tions.

Mechanical operation

The mechanical operation of the breaker should be checked by turning the breaker on and off several times.

SOURCE: HYDROELECTRIC RESEARCH AND TECHNICAL SERVICES GROUP

Caterpillar C175 Diesel Generator 2-4MW

The C175 family of diesel generator sets offers the most power you can get in any single high-speed package: 2-4MW.

One of the most significant components in the development of the C175 was the integration of ACERT™ Technology into the engine platform.

ACERT Technology is a synergistic approach utilizing a suite of complementary building block technologies that can be individually adapted to accommodate a specific application. In recent years, Caterpillar has spent more than $1 billion on the development of clean diesel technologies. Today, more than 330,000 engines are currently in operation with ACERT Technology, accumulating more than 2 million hours of use each day.

With the C175, the building blocks of ACERT Technology have been tailored to meet the current and pending emissions requirements of stationary diesel generator sets in a variety of applications.

Advantages

Thousands of hours of customer research created the foundation for the C175 design concept.

Some of the major advantages of the C175 family include:

• Proven Reliability with platform based on industry standard Cat® 3500 series, and supported by thousands of hours of lab and field-testing.
• Wider Power Range including 2000kW to 4000kW @ 1500 and 1800 rpm.
• Power Generation at Higher Speed than traditional medium speed products in the same power range.
• Higher Power Density equals more output from a given engine displacement / footprint, resulting in lower installed cost.
• Complete Package including SR5 generators, EMCP3 package controls and package/remote radiator with flexible controls packaging options simplifies installation.
• Lower Emissions meet U.S. EPA Tier 2 standards with a line of sight to meet U.S. EPA Tier 4 and EU Stage IIIB emissions levels.
• Lower Maintenance Costs due to increased oil change intervals, longer life (durability) of components and longer top end as well as full overhaul periods.
• Lower Operating Costs due to lower brake specific fuel consumption than competitive products.
• Systems Integration. The C175 electrical system components are engineered to work together with a wide range of products such as Uninterruptible Power Supplies (UPS), Automatic Transfer Switches (ATS), switchgear, remote monitoring services and customer building SCADA systems.
• Extensive Product Support from a worldwide dealer network with 24/7/365 parts and service availability.

Design Features

1. Fuel System

C175 - Fuel System

The new C175 engine features a Cat^® Common Rail Fuel System designed specifically for this engine platform.

Full Control of Both Fuel Delivery and Fuel Pressure At Any Load or Speed results in superior transient response and block load acceptance, as well as shorter recovery time.

More Compact single camshaft that is used only to open the intake and exhaust valves. It features a simpler injection design with no pumping function necessary.

Improved Cold Start Capability uses higher pressures at low speeds and produces less smoke.

„Fluid Containment“ Design. The high-pressure lines and rails are designed to provide outer concentric low-pressure containment. If a leak occurs in the high-pressure section, it leaks back to the outer low-pressure section and drains back to the tank.

Integrated Manifold or Monoblock offers a single point of connection to the engine, which eliminates leak paths while improving reliability.

Fuel Cooler Eliminated. Unlike the unit injector system, the Common Rail System used on the C175 does not require excess bypass fuel to cool the injector since injection pressure load is taken off the injector. The result is a reduction of heat generation in the return fuel and reduction in fuel flow rate by a factor of 4 when compared to the unit injector system. This eliminates the need for a fuel cooler in most cases.

Improved Fuel Filters. The C175 uses an eco-friendly fuel filter system. Instead of throwing away the whole canister, only the disposable non-metallic element inside the canister is changed.

Electronic Fuel Priming Pump is Engine Control Module (ECM)-controlled and offered as standard equipment. No manual effort is required to pump the fuel, so it’s more convenient and requires less operator effort.

2. Cooling System

C175 - Cooling System

The design philosophy for the Cat^® C175 cooling system is to minimize heat rejection by cooling only the parts that require cooling.

Inlet-Regulated System. The C175 features an innovative design unique to Caterpillar. The system senses the temperature at the inlet and controls the output providing more consistent temperatures and better control of oil viscosity than an outlet-regulated system.

Electronic Fluid Temperature Controller regulates inlet temperature of the coolant and allows for troubleshooting without removing the thermostat. Improved diagnostics enable the operator to pinpoint a problem quickly, which increases reliability and uptime.

Integral Water Supply and Return Manifold are built into the engine block to minimize connection points and bolted joints. This design helps contain fluids and improves overall engine reliability and serviceability.

Two-Stage After-Cooler. The first stage is cooled by a jacket water circuit and the second stage has a two-pass separate circuit. The after-cooler is constructed with tube fin cores that are more robust compared to the traditional bar plate fin design. The tubes of the core can be cleaned without removing the core from the engine, and the core can be remanufactured. The tubes also have more surface area per volume and less pressure drop, resulting in more efficient cooling. This after-cooler design also minimizes the size of the SCAC circuit, thereby reducing the size of the radiator. The location of the first stage jacket water core provides protection from high air temperatures. These features improve the durability and reliability of the cooling system.

3. Air Management

C175 - Air Management

Air management is one of the ACERT™ Technology building blocks used on the Cat^® C175 engine.

Crossflow Head provides separation between both the intake and exhaust ports and manifolds. The outboard air manifold location eliminates re-heating of intake air by preventing heat transfer from the exhaust to the intake. This results in reduced charge air temperature and increased charge air density, enabling higher power density as well as reducing SCAC cooling.

Taller Head accommodates larger ports and helps direct a large amount of cool air into the cylinder with the least resistance, resulting in the best port performance of any engine in the world. The taller head also accommodates increased valve lift of 22mm compared to 18mm on the Cat 3500, further improving breathing.

Improved Breathing. The tall crossflow head results in a greater amount of cooler air in and out of the engine, which helps produce higher power ratings and lower emissions. This, along with lower air pumping losses, results in lower fuel consumption.

New Generation of Turbochargers designed specifically for the C175. Four single-stage turbochargers provide a higher pressure ratio in a single stage. The turbocharger includes a cast titanium impeller and an improved bearing system that provides a higher load-bearing capacity and greater reliability, while increasing efficiency by 5% and extending the component life when compared to traditional cast aluminum impellers.

4. Lube System

C175 - Lube Management

The C175 lube system features two piston-cooling jets per piston.

A large capacity oil pump pressure regulation valve allows the engine to maintain optimum oil pressure at all speeds, loads and throughout the life of the engine, ultimately increasing durability.

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5. Core Engine Components

C175 - Core Engine Components

The components of the new C175 centerline engine are designed for higher strength, durability and compactness.

Crankshaft has a larger diameter to handle bigger loads. It is made of steel forged material and features induction hardened fillets and journals. Thrust plates are located at the rear end of the crankshaft to reduce motion inside of the coupling between the engine and generator.

Block is made of cast iron and provides increased strength and stiffness, and is lighter weight.

Mid-Support Liners provide stronger support to the liner and offer more efficient cooling by only cooling the top 25% of the cylinder liner. Mid-support liners allow for a smaller inside diameter of the combustion seal, as well as a higher position for the piston’s top ring. The result is reduced crevice volume, improved cooling and combustion efficiency, and reduced emissions. Mid-support liners allow the head bolts to be closer to the cylinder bore to minimize cylinder spacing and to create a more compact engine.

Cylinder Cuff is specially designed for improved durability. The ring of the „cuff“ located at the top of the cylinder scrapes off carbon accumulation on the piston top end, preventing the carbon from polishing, scratching or seizing the liner. The cuff also helps reduce crevice volume beside the piston, resulting in lower emissions.

Cylinder Head is made of iron for added strength. The tall C175 head helps eliminate the external water manifold by returning the coolant to the cylinder block.

Head Gasket features a simplified two-piece (carrier seal and combustion seal) design, shortening service time, decreasing parts costs, and increasing reliability and durability.

Pistons and Rings feature increased oil flow to pistons for better cooling and higher power ratings. Rectangular piston rings provide a superior seal and less motion, resulting in less wear and longer life. Piston, rod and liner come out as one assembly, resulting in faster, easier service.

Connecting Rods. Large diameter fracture split connecting rods provide better alignment between the rod and cap, which eliminates the need for a special alignment procedure.

Bearings. Large main and rod bearings provide better seizure resistance and better tolerance of a wide range of oil temperatures. Larger rod bearing and main bearing are more scuff and seizure resistant.

6. Engine Management System

C175 - Engine Management System

The Cat^® C175 utilizes much of the ACERT™ Technology electronics experience gained on small-bore engines and employs many new improvements and technologies more useful on large bore engines. The C175 Engine Management System exploits the power of modern control technology to improve reliability, exceed customer expectations and accommodate future customer requirements.

Engine Control Module (ECM). C175 engine controls use the latest version of the ADEM^™ A4 ECM to deliver 50 times the computing power of its predecessor. Specific benefits include monitoring over 30 points on the engine, driving up to 20 injectors, protecting the engine, communicating over 100 engine parameters to the customer, diagnosing and reporting on engine health. The ECM uses the latest advancements in ACERT Technology to improve engine performance while reducing emissions.

Engine Controls and Datalink. Three primary controllers are temperature control module, fuel high-pressure controller and ECM. These are connected to the engine J1939 datalink.

Rigid Wiring Harness. Metal enclosed rigid wiring harness system protects critical engine circuits from accidental damage, reducing service calls and increasing reliability.

Controls Packaging. The standard panel is a rear-mounted EMCP 3.1 with the option to upgrade to the EMCP 3.2 or EMCP 3.3.

7. Generator

C175 - Generator

Caterpillar is introducing the next evolution of generators, the SR5 Series, with the introduction of the C175 generator sets. The SR5 Series 1800 and 3000 frame generators have been designed specifically to work with the C175 engines. The structural design is matched to the C175 engine. Torsional and linear vibration analysis and testing have been performed to ensure durability.

The SR5 generator’s insulation system has been improved to meet insulation Class H. SR5 generators feature 2/3-pitch as standard on all low, medium and high voltage generators. SR5 generators have IP23 particle ingress protection.

Generator Set Packaging. The C175 uses a fusible coupling to connect the generator to the engine. All engines, generators and controls are tested individually prior to assembly. Once assembled, the entire generator set package is tested before shipping to dealers to ensure quality.

Applications

The versatility of the C175 makes it ideal for a variety of applications.

• Continuous – A continuous rating has a typical load factor of 70% to 100% with no limit on the number of hours per year. Typical peak demand is 100% of continuous rated kW for 100% of operating hours. Typical applications include base load, utility or co-generation.
• Prime – A prime rating has a typical load factor of 60% to 70% with no limit on the number of hours per year. Typical peak demand is 100% of prime rated kW with 10% overload available for emergency use for up to one hour in 12. Typical applications include industrial, pumping, construction, peak shaving or co-generation.
• Standby – A standby rating has a typical load factor of 70% or less with variable load for about 200 hours per year,with a maximum expected usage of 500 hours per year. Typical peak demand is 80% of the standby rated kW with power available for the duration of an emergency outage. Typical applications include building service standby or emergency standby.
• Load Management – A load management rating has a typical load factor of 100% of the prime rating for a maximum of 500 hours per year. Typical peak demand is 100% of the load management rating, with no overload available. Typical applications include base load or peak shaving.

SOURCE: Caterpillar C175

Lighting Fundamentals

Illuminance is light falling on a surface measured in footcandles or lux. Distributed with an economic and visual plan, it becomes engineered lighting and, therefore, practical illumination.

A lighting designer has four major objectives:

1. Provide the visibility required based on the task to be performed and the economic objectives.

2. Furnish high quality lighting by providing a uniform illuminance level, where required, and by minimizing the negative effects of direct and reflected glare.

3. Choose luminaires aesthetically complimentary to the installation with mechanical, electrical and maintenance characteristics designed to minimize operational expense.

4. Minimize energy usage while achieving the visibility, quality and aesthetic objectives.

CONTENTS

1. ILLUMINATION
2. LIGHT SOURCES
3. BALLASTS
4. LUMINAIRES

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1. ILLUMINATION

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1.1 Quantity of Illumination

Light Output

Light Output - Light Level - Brightness

The most common measure of light output (or luminous flux) is the lumen. Light sources are labeled with an output rating in lumens.

For example, a T12 40-watt fluorescent lamp may have a rating of 3050 lumens. Similarly, a light fixture’s output can be expressed in lumens. As lamps and fixtures age and become dirty, their lumen output decreases (i.e., lumen depreciation occurs).

Most lamp ratings are based on initial lumens (i.e., when the lamp is new).

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Light Level

Light intensity measured on a plane at a specific location is called illuminance. Illuminance is measured in footcandles, which are workplane lumens per square foot. You can measure illuminance using a light meter located on the work surface where tasks are performed. Using simple arithmetic and manufacturers’ photometric data, you can predict illuminance for a defined space. (Lux is the metric unit for illuminance, measured in lumens per square meter. To convert footcandles to lux, multiply footcandles by 10.76.)

Brightness

Another measurement of light is luminance, sometimes called brightness. This measures light „leaving“ a surface in a particular direction, and considers the illuminance on the surface and the reflectance of the surface.

The human eye does not see illuminance; it sees luminance. Therefore, the amount of light delivered into the space and the reflectance of the surfaces in the space affects your ability to see.

Quantity Measures

• Luminous flux is commonly called light output and is measured in lumens (lm).
• Illuminance is called light level and is measured in footcandles (fc).
• Luminance is referred to as brightness and is measured in footlamberts (fL) or candelas/m2 (cd/m2).

Determining Target Light Levels

The Illuminating Engineering Society of North America has developed a procedure for determining the appropriate average light level for a particular space. This procedure ( used extensively by designers and engineers ( recommends a target light level by considering the following:

• the task(s) being performed (contrast, size, etc.)
• the ages of the occupants
• the importance of speed and accuracy

Then, the appropriate type and quantity of lamps and light fixtures may be selected based on the following:

• fixture efficiency
• lamp lumen output
• the reflectance of surrounding surfaces
• the effects of light losses from lamp lumen depreciation and dirt accumulation
• room size and shape
• availability of natural light (daylight)

When designing a new or upgraded lighting system, one must be careful to avoid overlighting a space. In the past, spaces were designed for as much as 200 footcandles in places where 50 footcandles may not only be adequate, but superior. This was partly due to the misconception that the more light in a space, the higher the quality. Not only does overlighting waste energy, but it can also reduce lighting quality. Refer to Exhibit 2 for light levels recommended by the Illuminating Engineering Society of North America. Within a listed range of illuminance, three factors dictate the proper level: age of the occupant(s), speed and accuracy requirements, and background contrast.

For example, to light a space that uses computers, the overhead light fixtures should provide up to 30 fc of ambient lighting. The task lights should provide the additional footcandles needed to achieve a total illuminance of up to 50 fc for reading and writing. For illuminance recommendations for specific visual tasks, refer to the IES Lighting Handbook, 1993, or to the IES Recommended Practice No. 24 (for VDT lighting).

Quality Measures

• Visual comfort probability (VCP) indicates the percent of people who are comfortable with the glare from a fixture.
• Spacing criteria (SC) refers to the maximum recommended distance between fixtures to ensure uniformity.
• Color rendering index (CRI) indicates the color appearance of an object under a source as compared to a reference source.

1. ILLUMINATION ↑ | CONTENTS ↑ | TOP ↑

1.2 Quality of Illumination

Improvements in lighting quality can yield high dividends for US businesses. Gains in worker productivity may result by providing corrected light levels with reduced glare. Although the cost of energy for lighting is substantial, it is small compared with the cost of labor. Therefore, these gains in productivity may be even more valuable than the energy savings associated with new lighting technologies. In retail spaces, attractive and comfortable lighting designs can attract clientele and enhance sales.

Three quality issues are addressed in this section.

• Glare
• Uniformity of Illuminance on Tasks
  
• Color Rendition

Glare

Perhaps the most important factor with respect to lighting quality is glare. Glare is a sensation caused by luminances in the visual field that are too bright. Discomfort, annoyance, or reduced productivity can result.

A bright object alone does not necessarily cause glare, but a bright object in front of a dark background, however, usually will cause glare. Contrast is the relationship between the luminance of an object and its background. Although the visual task generally becomes easier with increased contrast, too much contrast causes glare and makes the visual task much more difficult.

You can reduce glare or luminance ratios by not exceeding suggested light levels and by using lighting equipment designed to reduce glare. A louver or lens is commonly used to block direct viewing of a light source. Indirect lighting, or uplighting, can create a low glare environment by uniformly lighting the ceiling. Also, proper fixture placement can reduce reflected glare on work surfaces or computer screens. Standard data now provided with luminaire specifications include tables of its visual comfort probability (VCP) ratings for various room geometries. The VCP index provides an indication of the percentage of people in a given space that would find the glare from a fixture to be acceptable. A minimum VCP of 70 is recommended for commercial interiors, while luminaires with VCPs exceeding 80 are recommended in computer areas.

Uniformity of Illuminance on Tasks

The uniformity of illuminance is a quality issue that addresses how evenly light spreads over a task area. Although a room’s average illuminance may be appropriate, two factors may compromise uniformity.

• improper fixture placement based on the luminaire’s spacing criteria (ratio of maxim recommended fixture spacing distance to mounting height above task height)
• fixtures that are retrofit with reflectors that narrow the light distribution

Non-uniform illuminance causes several problems:

• inadequate light levels in some areas
• visual discomfort when tasks require frequent shifting of view from underlit to overlit areas
• bright spots and patches of light on floors and walls that cause distraction and generate a low quality appearance

Color Rendition

The ability to see colors properly is another aspect of lighting quality. Light sources vary in their ability to accurately reflect the true colors of people and objects. The color rendering index (CRI) scale is used to compare the effect of a light source on the color appearance of its surroundings.

A scale of 0 to 100 defines the CRI. A higher CRI means better color rendering, or less color shift. CRIs in the range of 75-100 are considered excellent, while 65-75 are good. The range of 55-65 is fair, and 0-55 is poor. Under higher CRI sources, surface colors appear brighter, improving the aesthetics of the space. Sometimes, higher CRI sources create the illusion of higher illuminance levels.

1. ILLUMINATION ↑ | CONTENTS ↑ | TOP ↑

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2. LIGHT SOURCES

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Commercial, industrial, and retail facilities use several different light sources. Each lamp type has particular advantages; selecting the appropriate source depends on installation requirements, life-cycle cost, color qualities, dimming capability, and the effect wanted.

Before describing each of these lamp types, the following sections describe characteristics that are common to all of them.

2.1 Characteristics of Light Sources

Electric light sources have three characteristics: efficiency, color temperature, and color rendering index (CRI). Exhibit 4 summarizes these characteristics.

Efficiency

Some lamp types are more efficient in converting energy into visible light than others. The efficacy of a lamp refers to the number of lumens leaving the lamp compared to the number of watts required by the lamp (and ballast). It is expressed in lumens per watt. Sources with higher efficacy require less electrical energy to light a space.

Color Temperature

Another characteristic of a light source is the color temperature. This is a measurement of „warmth“ or „coolness“ provided by the lamp. People usually prefer a warmer source in lower illuminance areas, such as dining areas and living rooms, and a cooler source in higher illuminance areas, such as grocery stores.

Color temperature refers to the color of a blackbody radiator at a given absolute temperature, expressed in Kelvins. A blackbody radiator changes color as its temperature increases ( first to red, then to orange, yellow, and finally bluish white at the highest temperature. A „warm“ color light source actually has a lower color temperature. For example, a cool-white fluorescent lamp appears bluish in color with a color temperature of around 4100 K. A warmer fluorescent lamp appears more yellowish with a color temperature around 3000 K. Refer to Exhibit 5 for color temperatures of various light sources.

Color Rendering Index

The CRI is a relative scale (ranging from 0 – 100). indicating how perceived colors match actual colors. It measures the degree that perceived colors of objects, illuminated by a given light source, conform to the colors of those same objects when they are lighted by a reference standard light source. The higher the color rendering index, the less color shift or distortion occurs.

The CRI number does not indicate which colors will shift or by how much; it is rather an indication of the average shift of eight standard colors. Two different light sources may have identical CRI values, but colors may appear quite different under these two sources.

2. LIGHT SOURCES ↑ | CONTENTS ↑ | TOP ↑

2.2 Incandescent Lamps

Standard Incandescent Lamp

Standard Incandescent Lamp

Incandescent lamps are one of the oldest electric lighting technologies available. With efficacies ranging from 6 to 24 lumens per watt, incandescent lamps are the least energy-efficient electric light source and have a relatively short life (750-2500 hours).

Light is produced by passing a current through a tungsten filament, causing it to become hot and glow. With use, the tungsten slowly evaporates, eventually causing the filament to break.

These lamps are available in many shapes and finishes. The two most common types of shapes are the common „A-type“ lamp and the reflector-shaped lamps.

Tungsten-Halogen Lamps

The tungsten halogen lamp is another type of incandescent lamp. In a halogen lamp, a small quartz capsule contains the filament and a halogen gas. The small capsule size allows the filament to operate at a higher temperature, which produces light at a higher efficacy than standard incandescents. The halogen gas combines with the evaporated tungsten, redepositing it on the filament. This process extends the life of the filament and keeps the bulb wall from blackening and reducing light output.

Because the filament is relatively small, this source is often used where a highly focused beam is desired. Compact halogen lamps are popular in retail applications for display and accent lighting. In addition, tungsten-halogen lamps generally produce a whiter light than other incandescent lamps, are more efficient, last longer, and have improved lamp lumen depreciation.

Incandescent A-Lamp

More efficient halogen lamps are available. These sources use an infrared coating on the quartz bulb or an advanced reflector design to redirect infrared light back to the filament. The filament then glows hotter and the efficiency of the source is increased.

2. LIGHT SOURCES ↑ | CONTENTS ↑ | TOP ↑

2.3 Fluorescent Lamps

Fluorescent Lamps

Fluorescent lamps are the most commonly used commercial light source in North America. In fact, fluorescent lamps illuminate 71% of the commercial space in the United States.

Their popularity can be attributed to their relatively high efficacy, diffuse light distribution characteristics, and long operating life.

• Fluorescent lamp construction consists of a glass tube with the following features:
• filled with an argon or argon-krypton gas and a small amount of mercury
• coated on the inside with phosphors
• equipped with an electrode at both ends

Fluorescent lamps provide light by the following process:

• An electric discharge (current) is maintained between the electrodes through the mercury vapor and inert gas.
• This current excites the mercury atoms, causing them to emit non-visible ultraviolet (UV) radiation.
• This UV radiation is converted into visible light by the phosphors lining the tube.

Discharge lamps (such as fluorescent) require a ballast to provide correct starting voltage and to regulate the operating current after the lamp has started.

Full-Size Fluorescent Lamps

Full-size fluorescent lamps are available in several shapes, including straight, U-shaped, and circular configurations. Lamp diameters range from 1″ to 2.5″. The most common lamp type is the four-foot (F40), 1.5″ diameter (T12) straight fluorescent lamp. More efficient fluorescent lamps are now available in smaller diameters, including the T10 (1.25 „) and T8 (1″).

Fluorescent lamps are available in color temperatures ranging from warm (2700(K) „incandescent-like“ colors to very cool (6500(K) „daylight“ colors. „Cool white“ (4100(K) is the most common fluorescent lamp color. Neutral white (3500(K) is becoming popular for office and retail use.

Improvements in the phosphor coating of fluorescent lamps have improved color rendering and made some fluorescent lamps acceptable in many applications previously dominated by incandescent lamps.

Performance Considerations

The performance of any luminaire system depends on how well its components work together. With fluorescent lamp-ballast systems, light output, input watts, and efficacy are sensitive to changes in the ambient temperature. When the ambient temperature around the lamp is significantly above or below 25C (77F), the performance of the system can change. Exhibit 6 shows this relationship for two common lamp-ballast systems: the F40T12 lamp with a magnetic ballast and the F32T8 lamp with an electronic ballast.

As you can see, the optimum operating temperature for the F32T8 lamp-ballast system is higher than for the F40T12 system. Thus, when the ambient temperature is greater than 25C (77F), the performance of the F32T8 system may be higher than the performance under ANSI conditions. Lamps with smaller diameters (such as T-5 twin tube lamps) peak at even higher ambient temperatures.

Compact Fluorescent Lamps

Advances in phosphor coatings and reductions of tube diameters have facilitated the development of compact fluorescent lamps.

Manufactured since the early 1980s, they are a long-lasting, energy-efficient substitute for the incandescent lamp.

Various wattages, color temperatures, and sizes are available. The wattages of the compact fluorescents range from 5 to 40 ( replacing incandescent lamps ranging from 25 to 150 watts ( and provide energy savings of 60 to 75 percent. While producing light similar in color to incandescent sources, the life expectancy of a compact fluorescent is about 10 times that of a standard incandescent lamp. Note, however, that the use of compact fluorescent lamps is very limited in dimming applications.

The compact fluorescent lamp with an Edison screw-base offers an easy means to upgrade an incandescent luminaire. Screw-in compact fluorescents are available in two types:

• Integral Units. These consist of a compact fluorescent lamp and ballast in self-contained units. Some integral units also include a reflector and/or glass enclosure.
• Modular Units. The modular type of retrofit compact fluorescent lamp is similar to the integral units, except that the lamp is replaceable.

A Specifier Report that compares the performance of various name-brand compact fluorescent lamps is now available from the National Lighting Product Information Program („Screw-Base Compact Fluorescent Lamp Products,“ Specifier Reports, Volume 1, Issue 6, April 1993).

2. LIGHT SOURCES ↑ | CONTENTS ↑ | TOP ↑

2.4 High-Intensity Discharge Lamps

High-Intensity Discharge Lamps

High-intensity discharge (HID) lamps are similar to fluorescents in that an arc is generated between two electrodes. The arc in a HID source is shorter, yet it generates much more light, heat, and pressure within the arc tube.

Originally developed for outdoor and industrial applications, HID lamps are also used in office, retail, and other indoor applications. Their color rendering characteristics have been improved and lower wattages have recently become available ( as low as 18 watts.

There are several advantages to HID sources:

• relatively long life (5,000 to 24,000+ hrs)
• relatively high lumen output per watt
• relatively small in physical size

However, the following operating limitations must also be considered. First, HID lamps require time to warm up. It varies from lamp to lamp, but the average warm-up time is 2 to 6 minutes. Second, HID lamps have a „restrike“ time, meaning a momentary interruption of current or a voltage drop too low to maintain the arc will extinguish the lamp. At that point, the gases inside the lamp are too hot to ionize, and time is needed for the gases to cool and pressure to drop before the arc will restrike. This process of restriking takes between 5 and 15 minutes, depending on which HID source is being used. Therefore, good applications of HID lamps are areas where lamps are not switched on and off intermittently.

The following HID sources are listed in increasing order of efficacy:

• mercury vapor
• metal halide
• high pressure sodium
• low pressure sodium

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2.5 Mercury Vapor

Clear mercury vapor lamps, which produce a blue-green light, consist of a mercury-vapor arc tube with tungsten electrodes at both ends. These lamps have the lowest efficacies of the HID family, rapid lumen depreciation, and a low color rendering index. Because of these characteristics, other HID sources have replaced mercury vapor lamps in many applications. However, mercury vapor lamps are still popular sources for landscape illumination because of their 24,000 hour lamp life and vivid portrayal of green landscapes.

The arc is contained in an inner bulb called the arc tube. The arc tube is filled with high purity mercury and argon gas. The arc tube is enclosed within the outer bulb, which is filled with nitrogen.

Color-improved mercury lamps use a phosphor coating on the inner wall of the bulb to improve the color rendering index, resulting in slight reductions in efficiency.

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2.6 Metal Halide

These lamps are similar to mercury vapor lamps but use metal halide additives inside the arc tube along with the mercury and argon. These additives enable the lamp to produce more visible light per watt with improved color rendition.

Wattages range from 32 to 2,000, offering a wide range of indoor and outdoor applications. The efficacy of metal halide lamps ranges from 50 to 115 lumens per watt ( typically about double that of mercury vapor. In short, metal halide lamps have several advantages.

• high efficacy
• good color rendering
• wide range of wattages

However, they also have some operating limitations:

• The rated life of metal halide lamps is shorter than other HID sources; lower-wattage lamps last less than 7500 hours while high-wattage lamps last an average of 15,000 to 20,000 hours.
• The color may vary from lamp to lamp and may shift over the life of the lamp and during dimming.

Because of the good color rendition and high lumen output, these lamps are good for sports arenas and stadiums. Indoor uses include large auditoriums and convention halls. These lamps are sometimes used for general outdoor lighting, such as parking facilities, but a high pressure sodium system is typically a better choice.

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2.7 High Pressure Sodium

The high pressure sodium (HPS) lamp is widely used for outdoor and industrial applications. Its higher efficacy makes it a better choice than metal halide for these applications, especially when good color rendering is not a priority. HPS lamps differ from mercury and metal-halide lamps in that they do not contain starting electrodes; the ballast circuit includes a high-voltage electronic starter. The arc tube is made of a ceramic material which can withstand temperatures up to 2372F. It is filled with xenon to help start the arc, as well as a sodium-mercury gas mixture.

The efficacy of the lamp is very high ( as much as 140 lumens per watt. For example, a 400-watt high pressure sodium lamp produces 50,000 initial lumens. The same wattage metal halide lamp produces 40,000 initial lumens, and the 400-watt mercury vapor lamp produces only 21,000 initially.

Sodium, the major element used, produces the „golden“ color that is characteristic of HPS lamps. Although HPS lamps are not generally recommended for applications where color rendering is critical, HPS color rendering properties are being improved. Some HPS lamps are now available in „deluxe“ and „white“ colors that provide higher color temperature and improved color rendition. The efficacy of low-wattage „white“ HPS lamps is lower than that of metal halide lamps (lumens per watt of low-wattage metal halide is 75-85, while white HPS is 50-60 LPW).

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2.8 Low Pressure Sodium

Although low pressure sodium (LPS) lamps are similar to fluorescent systems (because they are low pressure systems), they are commonly included in the HID family. LPS lamps are the most efficacious light sources, but they produce the poorest quality light of all the lamp types. Being a monochromatic light source, all colors appear black, white, or shades of gray under an LPS source. LPS lamps are available in wattages ranging from 18-180.

LPS lamp use has been generally limited to outdoor applications such as security or street lighting and indoor, low-wattage applications where color quality is not important (e.g. stairwells). However, because the color rendition is so poor, many municipalities do not allow them for roadway lighting.

Because the LPS lamps are „extended“ (like fluorescent), they are less effective in directing and controlling a light beam, compared with „point sources“ like high-pressure sodium and metal halide. Therefore, lower mounting heights will provide better results with LPS lamps. To compare a LPS installation with other alternatives, calculate the installation efficacy as the average maintained footcandles divided by the input watts per square foot of illuminated area. The input wattage of an LPS system increases over time to maintain consistent light output over the lamp life.

The low-pressure sodium lamp can explode if the sodium comes in contact with water. Dispose of these lamps according to the manufacturer’s instructions.

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3. BALLASTS

All discharge lamps (fluorescent and HID) require an auxiliary piece of equipment called a ballast. Ballasts have three main functions:

• provide correct starting voltage, because lamps require a higher voltage to start than to operate
• match the line voltage to the operating voltage of the lamp
• limit the lamp current to prevent immediate destruction, because once the arc is struck the lamp impedance decreases

Because ballasts are an integral component of the lighting system, they have a direct impact on light output. The ballast factor is the ratio of a lamp’s light output using a standard reference ballast, compared to the lamp’s rated light output on a laboratory standard ballast. General purpose ballasts have a ballast factor that is less than one; special ballasts may have a ballast factor greater than one.

3.1 Fluorescent Ballasts

The two general types of fluorescent ballasts are magnetic and electronic ballasts:

Magnetic Ballasts

Magnetic ballasts (also referred to as electromagnetic ballasts) fall into one of the following categories:

• standard core-coil (no longer sold in the US for most applications)
• high-efficiency core-coil
• cathode cut-out or hybrid

Standard core-coil magnetic ballasts are essentially core-coil transformers that are relatively inefficient in operating fluorescent lamps. The high-efficiency ballast replaces the aluminum wiring and lower grade steel of the standard ballast with copper wiring and enhanced ferromagnetic materials. The result of these material upgrades is a 10 percent system efficiency improvement. However, note that these „high efficiency“ ballasts are the least efficient magnetic ballasts that are available for operating full-size fluorescent lamps. More efficient ballasts are described below.

„Cathode cut-out“ (or „hybrid„) ballasts are high-efficiency core-coil ballasts that incorporate electronic components that cut off power to the lamp cathodes (filaments) after the lamps are lit, resulting in an additional 2-watt savings per standard lamp. Also, many partial-output T12 hybrid ballasts provide up to 10% less light output while consuming up to 17% less energy than energy-efficient magnetic ballasts. Full-output T8 hybrid ballasts are nearly as efficient as rapid-start two-lamp T8 electronic ballasts.

Electronic Ballasts

In nearly every full-size fluorescent lighting application, electronic ballasts can be used in place of conventional magnetic „core-and-coil“ ballasts. Electronic ballasts improve fluorescent system efficacy by converting the standard 60 Hz input frequency to a higher frequency, usually 25,000 to 40,000 Hz. Lamps operating at these higher frequencies produce about the same amount of light, while consuming 12 to 25 percent less power. Other advantages of electronic ballasts include less audible noise, less weight, virtually no lamp flicker, and dimming capabilities (with specific ballast models).

There are three electronic ballast designs available:

Standard T12 electronic ballasts (430 mA)

These ballasts are designed for use with conventional (T12 or T10) fluorescent lighting systems. Some electronic ballasts that are designed for use with 4′ lamps can operate up to four lamps at a time. Parallel wiring is another feature now available that allows all companion lamps in the ballast circuit to continue operating in the event of a lamp failure. Electronic ballasts are also available for 8′ standard and high-output T12 lamps.

T8 Electronic ballasts (265 mA)

Specifically designed for use with T8 (1-inch diameter) lamps, the T8 electronic ballast provides the highest efficiency of any fluorescent lighting system. Some T8 electronic ballasts are designed to start the lamps in the conventional rapid start mode, while others are operated in the instant start mode. The use of instant start T8 electronic ballasts may result in up to 25 percent reduction in lamp life (at 3 hours per start) but produces slight increases in efficiency and light output. (Note: Lamp life ratings for instant start and rapid start are the same for 12 or more hours per start.)

Dimmable electronic ballasts

These ballasts permit the light output of the lamps to be dimmed based on input from manual dimmer controls or from devices that sense daylight or occupancy.

Types of Fluorescent Circuits

There are three main types of fluorescent circuits:

• rapid start
• instant start
• preheat

The specific fluorescent circuit in use can be identified by the label on the ballast.

The rapid start circuit is the most used system today. Rapid start ballasts provide continuous lamp filament heating during lamp operation (except when used with a cathode cut-out ballast or lamp). Users notice a very short delay after „flipping the switch,“ before the lamp is started.

The instant start system ignites the arc within the lamp instantly. This ballast provides a higher starting voltage, which eliminates the need for a separate starting circuit. This higher starting voltage causes more wear on the filaments, resulting in reduced lamp life compared with rapid starting.

The preheat circuit was used when fluorescent lamps first became available. This technology is used very little today, except for low-wattage magnetic ballast applications such as compact fluorescents. A separate starting switch, called a starter, is used to aid in forming the arc. The filament needs some time to reach proper temperature, so the lamp does not strike for a few seconds.

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3.2 HID Ballasts

Like fluorescent lamps, HID lamps require a ballast to start and operate. The purposes of the ballast are similar: to provide starting voltage, to limit the current, and to match the line voltage to the arc voltage.

With HID ballasts, a major performance consideration is lamp wattage regulation when the line voltage varies. With HPS lamps, the ballast must compensate for changes in the lamp voltage as well as for changes in the line voltages.

Installing the wrong HID ballast can cause a variety of problems:

• waste energy and increase operating cost
• severely shorten lamp life
• significantly add to system maintenance costs
• produce lower-than-desired light levels
• increase wiring and circuit breaker installation costs
• result in lamp cycling when voltage dips occur

Capacitive switching is available in new HID luminaires with special HID ballasts. The most common application for HID capacitive switching is in occupancy-sensed bi-level lighting control. Upon sensing motion, the occupancy sensor will send a signal to the bi-level HID system that will rapidly bring the light levels from a standby reduced level to approximately 80% of full output, followed by the normal warm-up time between 80% and 100% of full light output. Depending on the lamp type and wattage, the standby lumens are roughly 15-40% of full output and the input watts are 30-60% of full wattage. Therefore, during periods that the space is unoccupied and the system is dimmed, savings of 40-70% are achieved.

Electronic ballasts for some types of HID lamps are starting to become commercially available. These ballasts offer the advantages of reduced size and weight, as well as better color control; however, electronic HID ballasts offer minimal efficiency gains over magnetic HID ballasts.

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4. LUMINAIRES

A luminaire, or light fixture, is a unit consisting of the following components:

• lamps
• lamp sockets
• ballasts
• reflective material
• lenses, refractors, or louvers
• housing

Luminaire

The main function of the luminaire is to direct light using reflective and shielding materials. Many lighting upgrade projects consist of replacing one or more of these components to improve fixture efficiency. Alternatively, users may consider replacing the entire luminaire with one that I designed to efficiently provide the appropriate quantity and quality of illumination.

There are several different types of luminaires. The following is a listing of some of the common luminaire types:

• general illumination fixtures such as 2×4, 2×2, & 1×4 fluorescent troffers
• downlights
• indirect lighting (light reflected off the ceiling/walls)
• spot or accent lighting
• task lighting
• outdoor area and flood lighting

4.1 Luminaire Efficiency

The efficiency of a luminaire is the percentage of lamp lumens produced that actually exit the fixture. The use of louvers can improve visual comfort, but because they reduce the lumen output of the fixture, efficiency is reduced. Generally, the most efficient fixtures have the poorest visual comfort (e.g. bare strip industrial fixtures). Conversely, the fixture that provides the highest visual comfort level is the least efficient. Thus, a lighting designer must determine the best compromise between efficiency and VCP when specifying luminaires. Recently, some manufacturers have started offering fixtures with excellent VCP and efficiency. These so-called „super fixtures“ combine state-of-the-art lens or louver designs to provide the best of both worlds.

Surface deterioration and accumulated dirt in older, poorly maintained fixtures can also cause reductions in luminaire efficiency. Refer to Lighting Maintenance for more information.

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4.2 Directing Light

Each of the above luminaire types consist of a number of components that are designed to work together to produce and direct light. Because the subject of light production has been covered by the previous section, the text below focuses on the components used to direct the light produced by the lamps.

Reflectors

Reflectors are designed to redirect the light emitted from a lamp in order to achieve a desired distribution of light intensity outside of the luminaire.

In most incandescent spot and flood lights, highly specular (mirror-like) reflectors are usually built into the lamps.

One energy-efficient upgrade option is to install a custom-designed reflector to enhance the light control and efficiency of the fixture, which may allow partial delamping. Retrofit reflectors are useful for upgrading the efficiency of older, deteriorated luminaire surfaces. A variety of reflector materials are available: highly reflective white paint, silver film laminate, and two grades of anodized aluminum sheet (standard or enhanced reflectivity). Silver film laminate is generally considered to have the highest reflectance, but is considered less durable.

Proper design and installation of reflectors can have more effect on performance than the reflector materials. In combination with delamping, however, the use of reflectors may result in reduced light output and may redistribute the light, which may or may not be acceptable for a specific space or application. To ensure acceptable performance from reflectors, arrange for a trial installation and measure „before“ and „after“ light levels using the procedures outlined in Lighting Evaluations. For specific name-brand performance data, refer to Specifier Reports, „Specular Reflectors,“ Volume 1, Issue 3, National Lighting Product Information Program.

Lenses and Louvers

Most indoor commercial fluorescent fixtures use either a lens or a louver to prevent direct viewing of the lamps. Light that is emitted in the so-called „glare zone“ (angles above 45 degrees from the fixture’s vertical axis) can cause visual discomfort and reflections, which reduce contrast on work surfaces or computer screens. Lenses and louvers attempt to control these problems.

Lenses. Lenses made from clear ultraviolet-stabilized acrylic plastic deliver the most light output and uniformity of all shielding media. However, they provide less glare control than louvered fixtures. Clear lens types include prismatic, batwing, linear batwing, and polarized lenses. Lenses are usually much less expensive than louvers. White translucent diffusers are much less efficient than clear lenses, and they result in relatively low visual comfort probability. New low-glare lens materials are available for retrofit and provide high visual comfort (VCP>80) and high efficiency.

Louvers. Louvers provide superior glare control and high visual comfort compared with lens-diffuser systems. The most common application of louvers is to eliminate the fixture glare reflected on computer screens. So-called „deep-cell“ parabolic louvers ( with 5-7″ cell apertures and depths of 2-4″ ( provide a good balance between visual comfort and luminaire efficiency. Although small-cell parabolic louvers provide the highest level of visual comfort, they reduce luminaire efficiency to about 35-45 percent. For retrofit applications, both deep-cell and small-cell louvers are available for use with existing fixtures. Note that the deep-cell louver retrofit adds 2-4″ to the overall depth of a troffer; verify that sufficient plenum depth is available before specifying the deep-cell retrofit.

Distribution

One of the primary functions of a luminaire is to direct the light to where it is needed. The light distribution produced by luminaires is characterized by the Illuminating Engineering Society as follows:

• Direct ( 90 to 100 percent of the light is directed downward for maximum use.
• Indirect ( 90 to 100 percent of the light is directed to the ceilings and upper walls and is reflected to all parts of a room.
• Semi-Direct ( 60 to 90 percent of the light is directed downward with the remainder directed upward.
• General Diffuse or Direct-Indirect ( equal portions of the light are directed upward and downward.
• Highlighting ( the beam projection distance and focusing ability characterize this luminaire.

The lighting distribution that is characteristic of a given luminaire is described using the candela distribution provided by the luminaire manufacturer (see diagram on next page). The candela distribution is represented by a curve on a polar graph showing the relative luminous intensity 360 around the fixture ( looking at a cross-section of the fixture. This information is useful because it shows how much light is emitted in each direction and the relative proportions of downlighting and uplighting. The cut-off angle is the angle, measured from straight down, where the fixture begins to shield the light source and no direct light from the source is visible. The shielding angle is the angle, measured from horizontal, through which the fixture provides shielding to prevent direct viewing of the light source. The shielding and cut-off angles add up to 90 degrees.

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SOURCE: United States Enviromental Protection Agency

Motors for dusty atmospheres – a potentially explosive development

Industries dealing with solids handling, like food, pharmaceuticals and chemicals, must now use hazardous area motors, like the oil and gas industries have for many years. Combustible dust can be just as explosive as gas and needs to be treated accordingly.

These days, dust is classed as a hazardous atmosphere, on par with hazardous areas with combustible gas. For instance, in the food industry, substances such as grain, cereal, sugar, flour and milk powder are classed as hazardous when they are in the form of dust. Essentially, any combustible material can be highly volatile when reduced to dust. As dust, materials have an extremely large surface area and can burn rapidly. Under some conditions, this can cause an explosion with very high energy.

Since 2006, hazardous areas with dust come under the ATEX regulations that control installations in hazardous areas. Areas with dust are classified the same way as hazardous areas with gas and equipment is selected on the same basis. But while users in the chemical, oil and gas sectors have been dealing with hazardous atmospheres for decades, this is a fairly new field for many other industry sectors.

There are two types of potentially explosive atmospheres under ATEX, Group 1 for underground mines and Group ll for surface industries

In Group ll, ATEX defines categories of equipment, specified by their protection characteristics. It also designates the hazardous zones they can be used in. Hazardous areas are divided into three zones.

Hazardous dust

Motors for areas with hazardous dust are known as Dust Ignition Proof or DIP motors, alternatively Ex tD motors.

These are used in atmospheres where explosive dust surrounds the motor, or where dust settles under its own weight on the motor. They are designed for Zones 21 and 22; no motors can be used in Zone 20 or Zone 0.

Dust is measured either as a cloud of dust or a layer of dust. The ignition temperatures for various types of dust can be obtained from commercially available reference tables. The ignition temperature for a cloud of dust must be at least 50% above the motor’s marking temperature. The ignition temperature of a 5mm layer of dust must be 75°C above the marking temperature of the motor. It is the responsibility of the user to stage maintenance periods so that the dust layer does not build up above 5mm.

To decide whether hazardous area motors are needed, the ATEX regulations requires users to draw up an Explosion Protection Document, assessing each area of the plant for hazardous gas or dust and dividing the plant into zones. An area can be declared safe only as the result of a risk assessment. Once the plant is correctly divided into zones, the appropriate equipment for each zone can be selected.

It may be tempting to try and simplify the process by using a blanket zone to cover the entire site but this could be a mistake. More expensive, over-protected equipment will have to be bought, installed and inspected. The use of over-specified equipment can have long-term financial implications, as the maintenance and repair obligations under ATEX depend on the category of equipment. Blanket zoning also raises a suspicion that the risk analysis may not have been carried out in sufficient detail.

Manufacturers’ and users’ responsibilities

ATEX 95, the product directive, and ATEX 137, the worker protection directive, cover any electrical or mechanical product or equipment that constitutes a potential source of ignition risk and which requires a special design or installation procedure to prevent an explosion.
The Product Directive, ATEX 95, concentrates on the responsibilities of the equipment manufacturer. The directive draws up the distinction between the duties of the end-user, which include the definition of the Zones, and those of the manufacturer, who will be concerned with meeting the category requirements rather than the zones.
The Worker Protection Directive, ATEX 137, concentrates on the duties of the end-user. The directive requires a consistent assessment of all measures to prevent risks of explosions and injury to people both inside and outside the plant.

Safe operation of the product or equipment is the result of cooperation between the manufacturer, the end-user and, if involved, the contractor. However, the responsibility for explosion protection of the product or equipment can never be contracted out to a third party. While the end-user is responsible for installation of products and equipment, the motor manufacturer is responsible for safety of the motors and for delivering maintenance and installation instructions.

With responsibility divided up this way, responsibility for explosion safety rests squarely with either the equipment manufacturer or the end user. Nobody else can be held responsible. The manufacturer is responsible for the equipment being safe when it leaves the factory. The end user is responsible for ensuring that it is installed, maintained and operated in such a way that it does not pose a danger of explosion.

Employers are responsible for the actions of employees and suppliers. ATEX does allow outsourcing, but the end user is responsible for the quality and the end result of such work, for instance maintenance work. When equipment is to be repaired, the end user is responsible for selecting an appropriate repair shop.
Ex motors can be repaired or rewound, but this should only be done at an approved workshop. Repairs can be carried out either to IEC guidelines or to the manufacturer’s guidelines. If it is carried out to the manufacturers’ guidelines, all warranties and original documents continue to be valid. If not, it is the end user’s responsibility to ensure that the repair job is satisfactory. At the moment, ABB is the only manufacturer to offer certified premises for hazardous area motor repairs.

Drives and hazardous area motors

Drives and hazardous area motors

Variable speed drives can be used with hazardous area motors but certain considerations need to be kept in mind. For example, a variable speed drive may create extra losses inside the motor, because of its voltage-pulse based waveform, which is different to the sinusoidal waveform produced by the 50 Hz network.

Also, the air cooling of the motor will be affected by the speed of its fan.
The drive can also be the source of other undesirable side-effects, which can include reduced motor insulation life, electromagnetic interference and bearing currents. These are effects that can be prevented and for hazardous area duty, such prevention is essential.
An ATEX compliant drive system – including motors, sensors, cabling, filters etc – should be treated as a unit. The drive affects the motor performance and the motor affects the choice of drive. Matching your own motor/drive combination can be both time-consuming and difficult. Some manufacturers can supply a ready-made solution, with combined ATEX-approved drives and motors.

Assessing the risk

The decision on whether you need to employ hazardous area motors for dust depends on the results of a risk assessment.
First of all, you will need to identify and assess fire and explosion risks of dangerous substances.
EN Standard for Group ll: Dust environments

EN 61241 -0 General requirements

EN 61241 -1 Protection by enclosures tD

EN 50281 -1-1 Dust ignition protection

Keeping working areas clean and dust free, particularly near potential ignition sources, will go a long way to reducing risks, but the best advice is to employ a professional consultant. With relevant assistance, you will be able to assess the different areas of the plant, work out the zones and draw up detailed design documentation and inspection schedules for the plant.

You will then need to eliminate or reduce the risks from the use of these substances as much as possible. This could help make the hazardous area smaller, reducing safety risks as well as the costs.

‘Equipment for use in the presence of combustible dust’. One deciding factor is the type of dust, but a host of other factors also play their roles, such as particle size, moisture content and how the dust is formed.

SOURCE: Hazardex

Hydropower - Systems Overview

Continued from first part of article:
Hydropower – Systems Overview (1)

Generator

The generator converts the rotational energy from the turbine shaft into electricity.

Efficiency is important at this stage too, but most modern, well-built generators deliver good efficiency.

Direct current (DC) generators, or alternators with rectifiers, are typically used with small household systems, and are usually augmented with batteries for reserve capacity, as well as inverters for converting the electricity into the AC required by most appliances. DC generators are available in a variety of voltages and power outputs.

AC generators are typically used with systems producing about 3 KW or more. AC voltage is also easily changed using transformers, which can improve efficiency with long transmission lines.

A view into a turbine shows a relatively large (2 feet in diameter) Pelton wheel. Peltons vary in size from 3 inches to 13 feet or more, depending on head and flow.

Depending on your requirements, you can choose either single-phase or three-phase AC generators in a variety of voltages. One critical aspect of AC is frequency, typically measured as cycles per second (cps) or Hertz (Hz).

Most household appliances and motors run on either 50 Hz or 60 Hz (depending on where you are in the world), as do the major grids that interconnect large generating stations. Frequency is determined by the rotational speed of the generator shaft; faster rotation generates a higher frequency.

In battery-based hydro systems, the inverter produces an AC waveform at a fixed frequency. In batteryless hydro systems, the turbine controller regulates the frequency.

AC Controls

At the bottom of the penstock, a manifold routes water to the four nozzles of a Harris Pelton turbine that drives a permanent magnet alternator.

Pure AC hydro systems have no batteries or inverter. AC is used by loads directly from the generator, and surplus electricity is burned off in dump loads—usually resistance heaters.

Governors and other controls help ensure that an AC generator constantly spins at its correct speed. The most common types of governors for small hydro systems accomplish this by managing the load on the generator. With no load, the generator would “freewheel,” and run at a very high rpm. By adding progressively higher loads, you can eventually slow the generator until it reaches the exact rpm for proper AC voltage and frequency.

As long as you maintain this “perfect” load, known as the design load, electrical output will be correct. You might be able to maintain the correct load yourself by manually switching devices on and off, but a governor can do a better job— automatically.

By connecting your hydro system to the utility grid, you can draw energy from the grid during peak usage times when your hydro system can’t keep up, and feed excess electricity back into the grid when your usage is low. In effect, the grid acts as a large battery with infinite capacity.
If you choose to connect to the grid, however, keep in mind that significant synchronization and safeguards must be in place. Grid interconnection controls do both. They will monitor the grid and ensure that your system is generating compatible voltage, frequency, and phase. They will also instantly disconnect from the grid if major fluctuations occur on either end. Automatic disconnection is critical to the safety of all parties. At the same time, emergency shutdown systems interrupt the water flow to the turbine, causing the system to coast to a stop, and protecting the turbine from overspeed.

DC Controls

A DC hydro system works very differently from an AC system. The alternator or generator output charges batteries. A diversion controller shunts excess energy to a dump load. An inverter converts DC electricity to AC electricity for home use. DC systems make sense for smaller streams with potential of less than 3 KW.
AC systems are limited to a peak load that is equivalent to the output of the generator. With a battery bank and large inverter, DC systems can supply a high peak load from the batteries even though the generating capacity is lower.
Series charge controllers, like those used with solar- electric systems, are not used with hydro systems since the generators cannot run without a load (open circuit). This can potentially damage the alternator windings and bearings from overspeeding. Instead, a diversion (or shunt) controller must be used. These normally divert energy from the battery to a resistance heater (air or water), to keep the battery voltage at the desired level while maintaining a constant load on the generator.

The inverter and battery bank in a DC hydro system are exactly the same as those used in battery-based, solar-electric or wind-electric systems. No other special equipment is needed. Charge controller settings may be lower than used in typical PV and wind systems, since hydro systems are constant and tend to run with full batteries much of the time.

Head, Flow, & Efficiency

If you expect to sell electricity back to the utility, pay extra attention to the efficiency of your hydro system because higher output and a lower cost-per-watt will go straight to your bottom line. Your turbine manufacturer can give you guidance on the most efficient design, as well as grid interconnection controls and safeguards. If you’re off- grid, and your site doesn’t have lots of head and flow, high efficiency can make the difference between ample electricity for your needs and having to use a backup, gasoline- powered generator.

Click on turbine images to see enlarged:
A Canadian-made Energy Systems and Design turbine uses a permanent magnet alternator and a turgo runner.		A Power Pal turbine with a Francis runner direct-coupled to the alternator		The 4-inch (10 cm) turgo runner in an Australian-made Platypus turbine.		The underside of a low-head, high-flow Nautilus turbine showing the Francis runner, and above it, the innovative nautilus-shaped headrace.

Whether a hydro system generates a few watts or hundreds of megawatts, the fundamentals are the same. Head and flow determine how much raw water power is available, and the system efficiency affects how much electricity will come out the other end. Each component of a hydro system affects efficiency, so it’s worthwhile to optimize your design every step of the way.

More Hydro Terms

SOURCE: Dan New, homepower.com

Hydropower - Systems Overview

Hydropower is based on simple concepts. Moving water turns a turbine, the turbine spins a generator, and electricity is produced. Many other components may be in a system, but it all begins with the energy already within the moving water.

What Makes Water Power

Water power is the combination of head and flow. Both must be present to produce electricity. Consider a typical hydro system. Water is diverted from a stream into a pipeline, where it is directed downhill and through the turbine (flow). The vertical drop (head) creates pressure at the bottom end of the pipeline. The pressurized water emerging from the end of the pipe creates the force that drives the turbine. More flow or more head produces more electricity. Electrical power output will always be slightly less than water power input due to turbine and system inefficiencies.

Head is water pressure, which is created by the difference in elevation between the water intake and the turbine. Head can be expressed as vertical distance (feet or meters), or as pressure, such as pounds per square inch (psi). Net head is the pressure available at the turbine when water is flowing, which will always be less than the pressure when the water is turned off (static head), due to the friction between the water and the pipe. Pipeline diameter has an effect on net head.

Flow is water quantity, and is expressed as “volume per time,” such as gallons per minute (gpm), cubic feet per second (cfs), or liters per minute. Design flow is the maximum flow for which your hydro system is designed. It will likely be less than the maximum flow of your stream (especially during the rainy season), more than your minimum flow, and a compromise between potential electrical output and system cost.

Head and flow are the two most important things you need to know about your site. You must have these measurements before you can seriously discuss your project, how much electricity it will generate, or the cost of components. Every aspect of a hydro system revolves around head and flow. In Part 2 of this series, we will discuss how to measure them.

Power Conversion & Efficiency

The generation of electricity is simply the conversion of one form of energy to another. The turbine converts the energy in the moving water into rotational energy at its shaft, which is then converted to electrical energy by the generator. Energy is never created; it can only be converted from one form to another. Some of the energy will be lost through friction at every point of conversion. Efficiency is the measure of how much energy is actually converted. The simple formula for this is:

Net Energy = Gross Energy x Efficiency

While some losses are inevitable as the energy in moving water gets converted to electricity, they can be minimized with good design. Each aspect of your hydro system—from water intake to turbine-generator alignment to transmission wire size—affects efficiency. Turbine design is especially important, and must be matched to your specific head and flow for best efficiency.
A hydro system is a series of interconnected components. Water flows in at one end of the system, and electricity comes out the other. Here is an overview of these components, from the water source to the electrical controls.

Water Diversion (Intake)

This variable-flow, crossflow turbine uses a belt-drive coupling to a 40 KW synchronous generator.

The intake is typically the highest point of your hydro system, where water is diverted from the stream into the pipeline that feeds your turbine. A diversion can be as simple as a screened pipe dropped into a pool of water, or as big and complex as a dam across an entire creek or river. A water diversion system serves two primary purposes.

The first is to provide a deep enough pool of water to create a smooth, air-free inlet to your pipeline. (Air reduces horsepower and can damage your turbine.) The second is to remove dirt and debris.

Trash racks and rough screens can help stop larger debris, such as leaves and limbs, while an area of quiet water will allow dirt and other sediment to settle to the bottom before entering your pipeline. This helps reduce abrasive wear on your turbine.

Another approach is to use a fine, self-cleaning screen that filters both large debris and small particles.

Pipeline (Penstock)

Elements of a Hydroelectric System

The pipeline, or penstock, not only moves the water to your turbine, but is also the enclosure that creates head pressure as the vertical drop increases. In effect, the pipeline focuses all the water power at the bottom of the pipe, where the turbine is. In contrast, an open stream dissipates the energy as the water travels downhill.

Pipeline diameter, length, material, and routing all affect efficiency. Guidelines are available for matching the size of your pipeline to the design flow of your system. As you’ll see in the next article in this series, a small-diameter pipeline can considerably reduce your available horsepower, even though it can carry all available water.Larger diameter pipelines have less friction as the water travels through.

Powerhouse

The powerhouse is simply a building or box that houses your turbine, generator, and controls. Its main function is to provide a place for the system components to be mounted, and to protect them from the elements. Its design can affect system efficiency, especially with regard to how the water enters and exits your turbine. For example, too many elbows leading to the turbine can create turbulence and head loss.

Likewise, any restrictions to water exiting the turbine may increase resistance against the turbine’s moving parts.

Turbine

An in-stream screen keeps debris and silt out of the penstock at the small-stream intake for a microhydro system in Washington.

The turbine is the heart of the hydro system, where water power is converted into the rotational force that drives the generator. For maximum efficiency, the turbine should be designed to match your specific head and flow. There are many different types of turbines, and proper selection requires considerable expertise. A Pelton design, for example, works best with medium to high heads. A crossflow design works better with lower head but higher flow. Other turbine types, such as Francis, turgo, and propeller, each have optimum applications.

Turbines can be divided into two major types. Reaction turbines use runners (the rotating portion that receives the water) that operate fully immersed in water, and are typically used in low to moderate head systems with high flow. Examples include Francis, propeller, and Kaplan.
Impulse turbines use runners that operate without being immersed, driven by one or more high-velocity jets of water. Examples include Pelton and turgo. Impulse turbines are typically used with moderate-to-high head systems, and use nozzles to produce the high-velocity jets. Some impulse turbines can operate efficiently with as little as 5 feet (1.5 m) of head.

The crossflow turbine is a special case. Although technically classified as an impulse turbine because the runner is not entirely immersed in water, this “squirrel cage” type of runner is used in applications with low to moderate head and high flow. The water passes through a large, rectangular opening to drive the turbine blades, in contrast to the small, high-pressure jets used for Pelton and turgo turbines.
Regardless of the turbine type, efficiency is in the details. Each turbine type can be designed to meet vastly different requirements. The turbine system is designed around net head and design flow. These criteria not only influence which type of turbine to use, but are critical to the design of the entire turbine system.

Minor differences in specifications can significantly impact energy transfer efficiency. The diameter of the runner, front and back curvatures of its buckets or blades, casting materials, nozzle (if used), turbine housing, and quality of components all affect efficiency and reliability.

Drive System

The drive system couples the turbine to the generator. At one end, it allows the turbine to spin at the rpm that delivers best efficiency. At the other, it drives the generator at the rpm that produces correct voltage and frequency— frequency applies to alternating current (AC) systems only. The most efficient and reliable drive system is a direct, 1:1 coupling between the turbine and generator.

This is possible for many sites, but not for all head and flow combinations. In many situations, especially with AC systems, it is necessary to adjust the transfer ratio so that both turbine and generator run at their optimum (but different) speeds. These types of drive systems can use either gears, chains, or belts, each of which introduces additional efficiency losses into the system. Belt systems tend to be more popular because of their lower cost.

Hydro Terms

To be continued soon in next article: Hydropower – Systems Overview (2)

SOURCE: Dan New, homepower.com

ABB i-bus KNX - Constant lighting control

Lighting in modern buildings is more than a basic requirement – it can play an important role in the architectural design and the energy efficiency of the building, not to mention the health, safety and well being of the occupants.

With an impressive spectrum of products for the control, measurement, regulation and automation of lighting, ABB i-bus® EIB / KNX can perform challenging lighting tasks.

The following elaboration on the topic of constant lighting control should provide adequate background information to:
- better understand the method of operation of a constant lighting control
- ensure optimum placement of the light sensors required to detect the actual value
- recognise critical ambient conditions which interfere with the function of the constant lighting control
- evaluate the physical limitations to which a constant lighting control is subject.

For this purpose it is necessary to understand the most important terms used in the field of lighting technology.

How does constant lighting control function?

In constant lighting control a light sensor installed on the ceiling measures the luminance of the surfaces in its detection range, e.g. the floor or the desks.

This measured value (actual value) is compared with the predefined setpoint value, and the control value is adjusted so that the divergence between the setpoint and actual values is minimal. If it is brighter outside, the share of artificial lighting is reduced. If it is darker outside, the share of artificial lighting is increased. The exact function of the light controller is described in detail in the manual of the Light Controller LR/Sx.16.1.
A Luxmeter placed underneath the light sensor, e.g. on a desk, is used for setting the setpoint. This Luxmeter detects the degree of illumination which illuminates the surfaces underneath the light sensor.

The objective of a constant lighting control is to retain the set degree of illumination when a setpoint is set. To perfectly implement this objective, the light sensor should be placed exactly on the spot where the Luxmeter was placed to adjust the setpoint value, in order to also determine the degree of illumination. As this is not possible for practical reasons, the light sensor is generally mounted on the ceiling.

This is a compromise. For the reference setting of the setpoint, a Luxmeter is used for measurement of the degree of illumination; however, the light controller primarily detects the luminance underneath the light sensor. In this way the light controller indirectly maintains a constant degree of illumination. If certain constraints are not observed with indirect measurement, it can mean that the constant lighting control will not function or not function as required.

This is not a specific phenomenon just affecting our constant lighting control, but rather is the case for all constant lighting controls.

What is the difference between degree of illumination and luminance?

In order to fully appreciate the problems relating to indirect measurement, it is necessary to examine the most important terms used in lighting technology. Only the basic terms are explained and we will forego a more exact and detailed explanation or mathematical derivation of more complex terms, e.g. luminous intensity = luminous flux/steradian.
A luminary, e.g. a fluorescent tube, converts electrical energy to light. The light rays emitted by a light source (luminous exitance) are referred to as a luminous flux. The unit is the Lumen [lm]. Luminaries convert the input energy to light at varying degrees of efficiency.

In addition to the luminous flux there is the item luminous intensity, also referred to as the lumi- nous flux density. The luminous intensity is measured in Candelas [cd]. The Candela is a mea- surement unit for luminous intensity emitted by a light source in a particular direction. An exact definition will lead to a complex mathematical analysis, e.g. the explanation of a steradiant.

Simplification: A luminous intensity of 1 cd corresponds to the measured degree of illumination of 1 lx at a distance of 1 m from the light source.

The luminous flux emitted by the light source illuminates the surfaces that it meets. The intensity with which the surfaces are illuminated is referred to as the degree of illumination. The degree of illumination depends on the magnitude of the luminous flux and the size of the surfaces.
It is defined as follows:

E = Φ/ A [lx=lm/m²]

E = degree of illumination
Φ = luminous flux in lm
A = illuminated surface

In accordance with the above table, a 100 W incandescent lamp with 15 lm/W generates a maximum luminous flux of 1500 lm. If the entire luminous flux of the incandescent lamp is not emitted in a spherical manner into the room, but rather concentrated and distributed evenly on a surface of 1 m2, then the value for the degree of illumination at every point on the surface would be 1500 lx.

The perceived brightness of an illuminated surface depends on the illuminated surface and the reflectance of the illuminated surfaces. The reflectance is the reflected share of the luminous flux from the illuminated surface. Typical values for the reflectance are:

• 90% highly polished silver
• 75% white paper
• 65% highly polished aluminium
• 20% – 30% wood
• < 5% black satin

The perceived brightness of an illuminated surface or a self-illuminating surface, e.g. an LCD monitor, is designated as the luminance. The unit of luminance is cd/m².

If white paper is subject to a degree of illumination of 500 lx, then the luminance is about 130 – 150 cd/m². At the same degree of illumination, environmentally-friendly paper has a luminance of about 90 – 100 cd/m².

On what does the luminance measured by the light sensor respectively the measured value of the light sensor depend?

The luminance “primarily” detected by the light sensor depends on different criteria. It depends on the degree of illumination which the surfaces in the detection range of the light sensor are illuminated. The higher the degree of illumination, the higher the luminance of the illuminated surfaces.
The same applies for the reflectance of the surfaces. The higher the reflectance, the higher the luminance of the surfaces and thus the measured value of the sensor. The measured value of the sensor is the actual value used for lighting control.

The installed height of the sensor also plays a role. If the light sensor was an ideal “luminance measurement device”, then the luminance which it measures would be indepen- dent of the installation height of the light sensor. As this is not the case, the measured value of the sensor decreases as the installation height increases.

SOURCE: ABB | Practical Knowledge: ABB i-bus® KNX Constant lighting control

ePlusMenuCAD 9 - Advanced Electrical Design Tool

ePlusMenuCAD 9 is finally released! Since version 3, ePlusMenuCAD has been changed and improved a lot, and now, version 9 is fine polished and most complete version so far.

There are many improvements and some new things that will be very usefull to designers.

Many electrical designers use AutoCAD platform in their daily work. ePlusMenuCAD is an integrated tool within AutoCAD which contains almost every aspect of electrical design.

Few Words About ePlusMenuCAD 9

ePlusMenuCAD is a software tool for professonal electrical design in AutoCAD environment. If you do electrical design using AutoCAD, then you certainly know how much time you lose on inserting varius blocks of luminaires, sockets, panels, generating technical specifications, drawing single line diagrams, etc.

If you use your own blocks in AutoCAD which are placed somewhere on your HDD and insert them when needed in the drawing, and after that manually copy each time  – then ePlusMenuCAD is for you. All the symbols are placed in one place, available from the drop-down menu , 26 toolbars, and also from intuitive shorcuts from command line. No more boring inserting and copyng blocks! ePlusMenuCAD offers efficency and high speed in generating technical specifications for Bill of Quantities, as well as automation in inserting electrical symbols into drawing.

In ePlusMenuCAD there are two modules integrated: Mosaic Design and X-functions. Mosaic Design is advanced tool for creating single line diagrams and application diagrams. Large database of (universal) symbols covers almost any kind of scheme. Insertion of symbols and feeders, and generation of BOM is completely automated and very easy for use in drawing. Second module X-functions, has more than 50 extra usefull functions (commands) that saves a lot of time durin daily work in AutoCAD. Working with layers, blocks, polylines  etc. is much much easier .

ePlusMenuCAD can be translated in to two languages English and Serbian/Croatian.

Example

Example of using ePlusMenuCAD in project Hotel Splendid in Budva (Montenegro), where it was used for designing lighting, power distribution,  technology, installations of sockets and single line diagrams.

AutoCAD support

AutoCAD versions 2006, 2007, 2008, 2009 and 2010 are fully supported, and ePlusMenuCAD can be installed and used simultany on this versions. That means that ones ePlusMenuCAD is installed, you can use it in all (supported) installed AutoCAD versions.

Conception

ePlusMenuCAD drop-down menu (click to enlarge)

More than 1200 electrical symbols are placed in its categories (outlets, luminaires, types of installation, DEA, Cable verticals, labels of cables, transformers, cable feeds, TKS, EIB KONNEX ..). Every category has its layer. Layers carry the prefix „EnJS_“ and „EnTS_“ so that can be easily sorted in Layer Manager in the AutoCAD.

Also, there are a lot of various types of luminaires from metal-halid throug incadescent sorted by category and with predict shortcuts from the command line. Lamps that are designed to be supplied rom Diesel Agregate DEA, have cross symbol, and as such are also located in generated technical specification. Almost every area in which there are elements is covered with IEC symbols.

Drop-down menu is well organized, all symbols and functions are divided into categories, the most important are shown below:

Electrical distribution of power
• Predefined types of power supply lines (network, aggregate, UPS, diesel supply…)
• Power transformers – dry type and distribution oil transformers (with and without conservator) typical powers 630, 1000, 1600, 2000, 2500 and 3200kVA
• Distribution boards and panels, panels supplied from diesel agregate, and all with labels
• Cable or busbar vertical runs with their labels of incoming or outgoing connections
• Predefined labels for the cables in the colors (to distinguish cables of differnt type and supply…)

Installation of power sockets
• Power sockets 2P and 3P in the IEC variations and variations GOST standards (Russian standard)
• TV, antenna, computer plug and terminal space in the floor, fan-coil connection…
• Thermostats, rails for the main and additional equipotential deuce …
• Cable feeds for direct consumers, in wall and ceiling (2P, 3P), luminaires

Power and distribution transformers 10-20/0, 4kV
• Dry type transformer, powers: 630kVA – 3200kVA
• Oil type transformers, powers: 630kVA – 2500kVA with and without conservator

Installation of earthing
• Vertical runs of FeZn earthing bar (predefined in various colors)
• Tables for power sockets, cable feeds, lamps, and elements of Earthing with predefined default values

Legends
• Legends for the power sockets, luminaires, electric distribution and cables (2p and 3p)
• Stamp basis (the ability to post the logo of your company)
• Unique symbol of current round ECM
• The automatic marking ECM and (increasing, decreasing or all of the same series)

Installation of lighting
• Fluoroscent lamps built-in and built-on, powers from 1×18W to 4×36W with DEA symbols
• Fluroscent tubes, powers from 1×18W to 2×36W
• Fluo-compact lamps built-in and built-on, powers from 1×9W to 2×36W with DEA symbols
• Incadescent lamps, built-in and built-on, powers from 40W to 100W with DEA symbols
• Incadescent-reflect lamps, built-in and built-on, with DEA symbols
• Halogen lamps built-in and built-on, powers from 20W to 1000W with DEA symbols
• Metal-halid lamps built-in and built-on, powers from 70W do 2000W with DEA symbols
• Reflectors
• Crystal chandeliers for the salons and kitchen
• Decorative lamps for billiard tables, halls, theaters…
• Lamps for outdoor lighting (pillars, underwater lamps …)
• Anti-panic lamp
• Sensors and feeds the optical cable …
• Installation switches, 2p, 3p, alternate, serial …
• Dimers, tasters…

Telecommunications and signal systems
• predefined types of installations (fire, access control, anti-burglary, structural wiring…)
• Anti-burglary
• Anti-fire
• Access control
• Video surveillance – CCTV
• TV and Radio
• Phone and intercom
• Clock
• Gas
• Audio-Video Systems
• Speakers
• Power supply
• Wireless transfer of information

EIB KONNEX
• Instabus elements (system, input / output, lighting, heating / cooling, display, infrared …)

What can be designed with ePlusMenuCAD?

Highlights:

MOSAIC DESIGN: ePlusMenuCAD is fully capable to draw single line diagrams and application schemes using built-in modul Mosaic Design. Main feature is the fact that all pages of scheme are in one DWG drawing, and that user can create complete distributive or motor feeders in a minute, just by picking on one of the many predefined feeders.User can also plot one or  one hunderd and one scheme just with one click. All elements and feeders are intuitive sorted in iNteLLi Elements, with options of zoom preview of each element or feeder. Mosaic Design runs when you open one of it’s templates from default folder (new drawing). There are several offered templates that are copied during installation of ePlusMenuCAD in default AutoCADs template folder. Now, all you have to do is to choose one  template and Mosac Design module will be automatically loaded, and you can use any command from the menu or a toolbar. You can also simply change existing template and save it as your own template .

SCALE FACTOR: All symbols (blocks) in ePlusMenuCAD are defined by ScaleFactor. This is the scale of symbols with respect to the drawing. Default value is 1, but it can be changed at any time to any positive value. Symbols of electric current mark ECM and tables of power sockets and luminaires have scale factor SFecm, and symbol of junction box has its scale factor SFjb. In this way, you can intelligently control the scale of symbols in the drawing. Scale can therefore  be changed very easy. If you don’t want to think about the Scale Factor, then set the Master SF to some value that applies to all drawings.

InfoIt PRO: Is a function to be used for generating Bill of Quantaties as well as for getting a lot of information about the symbols in the drawing. What can you do with InfoIt? You can take out a detailed technical specification from DWG drawing, calculate installed single-phase and three-phase el. powers of sockets and cable feeds from their tables, export report to MS Word, take out a list of all non-ePlusMenuCAD blocks, take out all luminaires by tags. InfoIt PRO is integrated part of ePlusMenuCAD. InfoIt Database is a unique datsbase of blocks that are within ePlusMenuCAD, and it offers the possibility to add your own symbol definitions – your own blocks . It is also possible to edit descriptions of all blocks in the InfoIt Database.

iNaLL Professional 6: A unique tool for every-day work in AutoCAD. It can make changes in the content of text objects TEXT, MTEXT, ATTRIBUTE, BLOCK, DIM. Inall PRO can store any text that you select into internal memory, so you can use it later in some other drawing. It has the support of the Serbian latin letters ČĆĐŠŽ, as well as all Russian letters, which can be used with any font. You can also import content of any text file into iNaLL PROs memory and use it for pasting in text  objects in drawing.

Download link: Here

Stručni tekst autora Dardan Klimenta, Viktor Kuč i Jordan Radosavljevic

U ovom radu su predstavljene mogućnosti nastanka kvarova kod podzemnih kablovskih vodova usled radova na uklanjanju korenja okolnog visokog rastinja i ukazano je na potrebu da se tehnički propisi koji se trenutno koriste u Republici Srbiji i Republici Crnoj Gori moraju dopuniti regulativama koje bi propisale načine polaganja kablova u blizini visokog rastinja.

Razmatrana problematika je ilustrovana na autentičnom primeru kvara koji se dogodio 14. novembra 2007. godine na podzemnom 0.4 kV-om kablovskom vodu instaliranom u Bijelom Polju u Republici Crnoj Gori. Simulacija nelinearne tranzijentne raspodele temperaturnog polja izvršena je pomoću softvera baziranog na metodi konačnih elemenata.

1. UVOD

Pojedina poglavlja kablovske tehnike postaju interesantna tek onda kada se u distributivnoj mreži ili u nekom od industrijskih ili elektroenergetskih postrojenja dogodi kvar. Tako je ovom prilikom u prvi plan izbio međusobni odnos podzemnih energetskih kablova i korenja visokog rastinja. U odsustvu domaćih propisa koji bi uredili ovu problematiku, bilo je pitanje vremena kada će se na nekom podzemnom kablovskom vodu dogoditi kvar izazvan dejstvom korenja. Kvar te vrste dogodio se 14. novembra 2007. godine na podzemnom 0.4 kV-nom kablovskom vodu koji povezuje transformatorsku stanicu 10/0.4 kV/kV ′′Bjelasica′′ i industrijsko postrojenje za proizvodnju mleka i mlečnih proizvoda A. D. Krisma Milk – Bijelo Polje u R. Crnoj Gori. Uticaj vegetacije na podzemne energetske kablove do sada nije značajnije diskutovan u domaćim i inostranim naučno- tehničkim krugovima. Ukoliko se to i događalo pokušaji su se svodili na merenje i izračunavanje specifičnog toplotnog otpora zemljišta duž kablovske trase radi konstatacije isušivanja zemljišta u blizini visokog rastinja [1,2].

Veliki broj IEEE publikacija kao što je [3] bavi se raspodelom temperaturnog polja i kretanjem vlage u okolini podzemnih kablovskih vodova ali ne i problematikom polaganja kablova u blizini visokog rastinja. IEC standardi koji propisuju postupke izračunavanja strujnih opterećenja kablova za različite uslove polaganja kablova takođe ne dotiču ovu problematiku [4-6]. Propisi EPS-a takođe ne regulišu način polaganja energetskih kablova u blizini visokog rastinja [7], ali se isti u domaćoj praksi polažu na najmanje 2 m od visokog rastinja, tj. od stabala drveća. Navedeno rastojanje je preuzeto iz internih propisa gradskog zelenila grada Beograda [9,10]. Međutim, propisi preduzeća koja se bave održavanjem gradskog zelenila mogu važiti samo za uslove izvođenja radova iz domena njihove delatnosti ali ne i za projektovanje kablovskih vodova zbog postojanja niza tehničkih faktora koji bi trebali biti obuhvaćeni njima a nisu.

U svetu nije retko iskustvo i da vlada neke države donese paket propisa koji u celosti uređuje ovu problematiku kao što je to učinilo Ministarstvo ekonomskog razvoja Novog Zelanda [8]. Tako prema [8] odstojanje korenja visokog rastinja od podzemnih kablovskih vodova ne može biti manje od 0.5 m. Ovo se u biti razlikuje od onoga što se radi u našoj praksi gde se može dogoditi da podzemni kablovski vod prođe i kroz gust splet korenja.
Nemački standardi nalažu da se kablovi polažu na 2.5 m od stabala drveća [10]. Ako se pomenuto rastojanje ne može ispoštovati onda se kablovi provlače kroz cevi koje se polažu bušenjem ili utiskivanjem [10]. Prema ruskoj literaturi predviđa se da ovo rastojanje iznosi 2 m, ali se ostavlja mogućnost da se u dogovoru sa nadležnom kompanijom ono može i smanjiti [10]. Nepostojanje domaćih propisa u ovoj oblasti, okolnosti nastanka razmatranog kvara i minoran broj publikacija na ovu temu u svetu, bili su povod za pisanje ovog rada i iniciranje dopune tehničkih propisa koji se koriste u elektroprivredama R. Srbije i R. Crne Gore.

2. FORMULACIJA PROBLEMA

Proboj jedne od faza podzemnog 0.4 kV- nog kablovskog voda koji je trasiran između TS 10/0.4 kV/kV ′′Bjelasica′′ i industrijskog postrojenja za proizvodnju mleka i mlečnih proizvoda A. D. Krisma Milk – Bijelo Polje dogodio se 14. novembra 2007. u 3 h i 15 min. Nastanku ovog kvara prethodili su neadekvatni ambijentni uslovi u zemljištu oko kabla i mehaničko oštećenje izolacije kabla. Razmatrani kabl je tipa PP 00-AS 4×120 mm² i nazivnog napona 0.6/1 kV. Uzroke za loše ambijentne uslove u zemljištu i mehaničko oštećenje kabla ovom prilikom treba tražiti u: (i) nepostojanju propisa koji bi uredili problematiku polaganja kablova u blizini visokog rastinja, (ii) nepostojanju propisa koji bi definisali postupke uklanjanja visokog rastinja u blizini podzemnih instalacija i (iii) višednevnim padavinama koje su prethodile nastanku kvara.

Poznato je da visoko rastinje isušuje zemljište i otežava zadržavanje vlage u njemu. Prema vrednostima specifičnih toplotnih otpora zemljišta izmerenim na mestima gde kablovski vodovi prolaze pored visokog rastinja i gde nema vegetacije proizilazi da se ova prva mogu smatrati toplotno kritičnim već u nominalnim režimima eksploatacije kablova. Za delove trase u blizini visokog rastinja vrednosti specifičnih toplotnih otpora kablovske posteljice i okolnog zemljišta dostižu 2 °C⋅m/W i 4 °C⋅m/W, respektivno [1]. One su bile dvostruko veće od njima odgovarajućih vrednosti u oblastima bez vegetacije [1].

Slika 1. Raspored stabala topole u odnosu na položaj trase podzemnog 0.4 kV-nog kablovskog voda, mesto kvara i zgradu postrojenja za proizvodnju mleka i mlečnih proizvoda A. D. Krisma Milk – Bijelo Polje. EK – energetski kabl tipa PP 00-AS 4×120 mm2, nazivnog napona 0.6/1 kV i ukupne dužine 293.5 m (sa rezervom); T – stabla topole; K – mesto kvara; R – rezerva kabla dužine 5 m i dozvoljenog poluprečnika savijanja 0.8 m.

Porast vrednosti specifičnog toplotnog otpora zemljišta jeste bitan termički aspekt eksploatacije podzemnih kablovskih vodova u blizini visokog rastinja ali ne i jedan od uzroka kvara na posmatranom 0.4 kV-nom kablovskom vodu. Ovom prilikom je interesantnije osvrnuti se na mehanička naprezanja i oštećenja kablova usled dejstva korenja visokog rastinja.

Pojedine vrste drveća imaju vrlo snažno i „agresivno“ (brzorastuće) korenje tako da se o tome mora voditi računa još u fazi projektovanja podzemnih kablovskih vodova. Izraziti predstavnici takvog drveća su topole koje su i uzrok ovde razmatranog kvara. Žile korena topole po horizontali se od svojih stabala udaljavaju i po više od 30 m [11]. Veličina i razvijenost korena topole zavise od faktora kao što su njena vrsta, starost, geografska zona i sl.

Raspored stabala topole u odnosu na položaj trase podzemnog 0.4 kV-nog kablovskog voda, mesto kvara i zgradu postrojenja prikazan je na slici 1. Današnja zgrada postrojenja do 1980. godine služila je drugoj nameni a električnom energijom je snabdevana preko danas nepostojećeg nadzemnog voda. Sa prilagođavanjem zgrade današnjim potrebama rešeno je da se pređe na napajanje preko podzemnog kablovskog voda koji bi po prenosnoj moći odgovarao potrošnji postrojenja.

Osnovni razlog zašto je ovaj kabl 1980. položen u zemljište gde se prepliće korenje topola starih po 41 godinu bilo je nepostojanje propisa koji bi to tada sprečio ili naložio da se to izvede na tehnički valjan način. Izuzev dubine polaganja na pojedinim mestima, svi ostali tehnički propisi, kao što su rezerva, vijuganje, poluprečnik savijanja, upozoravajuća traka i sl., ispoštovani su i prema danas vežećim propisima [4-7]. U prilog lošem izboru trase kabla tada je išla i činjenica da je ondašnji plan uređenja zelene površine ispred zgrade postrojenja predviđao i zadržavanje postojećeg drvoreda što se svakako pokazalo pogrešnim.

Slika 2. Hronološki prikaz radova i uslova koji su prethodili nastanku kvara na podzemnom 0.4 kV-nom kablovskom vodu. a) polaganje kabla; b) ambijentni uslovi u zemljištu tokom perioda eksploatacije kabla bez oštećenja izolacije; c) radovi na uklanjanju vegetacije: sečenje stabala, vađenje panjeva i izravnanje terena; d) ambijentni uslovi u zemljištu tokom perioda eksploatacije kabla sa oštećenjem izolacije; e) periodične padavine.

Na slici 2 dat je hronološki prikaz radova i uslova koji su prethodili nastanku kvara na podzemnom 0.4 kV-nom kablovskom vodu. Odstupanje od propisa na mestu kvara dogodilo se još u fazi polaganja kabla kada je isti položen direktno u zemlju na dubini od 0.5 m umesto na propisanih 0.7 m (slika 2a). Kabl je na ostatku trase položen na 0.7 m. Razlog za polaganje kabla na dubini različitoj od propisane bio je gust splet korenja na koji se tada naišlo prilikom iskopavanja rova.
Brz razvoj korenja doveo je do toga da je zemljište u kablovskom rovu već posle godinu dve bilo prožeto žilama korenja a kabl izložen mehaničkom naprezanju od strane njih (slika 2b).
Do mehaničkog oštećenja izolacije kabla dolazi 17. juna 2007. za vreme radova na uklanjanju vegetacije (slika 2c). Vađenje panjeva je izvršeno pomoću bagera i definitivno je uzrok oštećenja kabla. Prilikom izvlačenja jednog od panjeva čije je korenje obavijalo kabl neizbežno je došlo do zatezanja jedne žile korena, njenog usecanja u izolaciju kabla i konačno njenog kidanja.
Po vađenju panjeva, izravnavanju terena i nabijanju zemljišta, u periodu od 17. juna do 10. novembra 2007., imala se eksploatacija kabla sa mehanički oštećenom izolacijom u zemljištu gde je preostalo dosta pokidanih žila korenja (slika 3d). U tom periodu uticaj ionako malih padavina bio je zanemarljiv iz sledećih razloga: (i) u periodu od 01. juna do 30. septembra 2007. vršena je rekonstrukcija objekta i remont opreme tako da je postrojenje bilo van funkcije a kabl opterećen samo snagom osvetljenja objekta i električnih alata korišćenih tom prilikom i (ii) u periodu pogona postrojenja od 01. oktobra do 10. novembra 2007. nije bilo značajnijih padavina.
Period količinski značajnijih padavina počinje 10. novembra 2007. i nastavlja se sve do nastanka kvara na kablu 14. novembra 2007. (slika 2e).

3. MODELIRANJE I SIMULACIJA KVARA

Priprema modela konačnih elemenata za jedan nelinearni termodinamički sistem kao što je podzemni kabl pogođen jednofaznim zemljospojem nije nimalo lak zadatak. Za diskusiju u ovom radu od značaja će biti samo temperature provodnika i izolacije kabla ali ne i raspodela temperature u okolnom zemljištu tako da bi rešavani domen većih dimenzija bio suvišan. Izborom domena trakastog oblika koji bi obuhvatio poprečni presek kabla na mestu kvara i površinu zemlje kao granicu sa definisanim graničnim uslovom konvekcije otvara se mogućnost da se za proračun upotrebi nekomercijalna verzija softverskog paketa QuickField 5.5.

Naime, ovaj softverski alat ima ograničenje (postavljeno od strane proizvođača) i njime se unutar rešavanog domena ne može generisati mreža koja bi imala više od 255 čvorova. Umrežena geometrija rešavanog domena prikazana je na slici 3.

Slika 3. Umrežena geometrija poprečnog preseka rešavanog domena.

Za model konačnih elemenata sa slike 3 važi: (i) njegove spoljašnje dimenzije su 100 mm × 526 mm; (ii) sastoji se od 7 blokova: okolno zemljište, PVC izolacija, četiri aluminijumska provodnika i deo mehanički oštećene PVC izolacije; (iii) mreža ima ukupno 227 čvorova; (iv) poprečni preseci sektorskih provodnika kabla zamenjeni su njima ekvivalentnim okruglim provodnicima prečnika 12.4 mm; (v) konstruktivni podaci kabla sa ekvivalentnim provodnicima kružnog preseka su: debljina izolacije provodnik-provodnik 3.2 mm, debljina spoljašnjeg plašta 2.4 mm i spoljašnji prečnik kabla 41.5 mm; (vi) raspored provodnika u kablu izvršen je u smeru kretanja kazaljke na časovniku na sledeći način: faza A – faza B – faza C – neutralni provodnik, počevši sa provodnikom koji je najudaljeniji od površine zemlje; (vii) pretpostavljeno je da se mehaničko oštećenje izolacije dogodilo uz provodnik faze A; (viii) blok kojim je modelirano mesto mehaničkog oštećenja izolacije zasenčen je na slici i ima termofizičke karakteristike okolnog zemlji�