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Arc-resistant low voltage switchgear

Arc-resistant low voltage switchgear

For years, electrical equipment has been designed to withstand and deal with the issue of bolted faults, where the current spikes to a dangerously high level but is safely interrupted by the protective devices contained in the equipment (breakers, fuses and relays). However, these devices typically do not detect and interrupt dangerous internal arcing faults, which have a lower current level, but can generate a far more dangerous scenario for operating personnel.

Arc faults can be caused by a breakdown of insulation materials, objects coming into close proximity with the energized bus assembly, even entry of rodents or other animals into the equipment. The thermal energy created by these events can get as high as 35,000ºF, melting materials and clothing from several feet away. Also consider that the arc blast produced by a lineup of 480 Vac switchgear rated at 85 kA can be equivalent to 20.7 lbs of TNT!

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So, what is the solution?

Eaton’s solution: arc-resistant low voltage switchgear

Eaton introduces the addition of an ANSI Type 2 arc-resistant low voltage switchgear offering to its current product line. This is the latest release in arc-safe equipment from Eaton’s Electrical Sector. The arc-resistant low voltage switchgear protects operating and maintenance personnel from dangerous arcing faults
by redirecting or channeling the arc energy out the top of the switchgear, regardless of the origination location of the arc.

Eaton’s arc-resistant low voltage switchgear has been successfully tested to ANSI C37.20.7 at KEMA-Powertest, and has been ULT witnessed and certified.

Standard features
  • Ratings:
    • Up to 100 kA short circuit at 508 Vac maximum and up to 85 kA short circuit at 635 Vac maximum
    • Up to 10 kA horizontal main bus continuous current
    • Up to 5 kA vertical bus continuous current
    • MagnumE DS power circuit breaker frame ratings between 800A and 6000A
  • ANSI Type 2 arc-resistant design protects the operator around the entire perimeter of the equipment
  • Floor-to-ceiling height of 10 feet required whether exhausting into a room or through an arc plenum
  • Strengthened one-piece breaker door and latches
  • Dynamic flap system on rear ventilation openings that remain open under normal operating conditions, but close during an arcing event to prevent dangerous gasses from escaping
  • Patented bellows design allowing drawout of breaker into the disconnected position with the door closed, while simultaneously protecting the operator from any dangerous gasses during an arc event
  • Patented venting system that directs arc gasses out the top of the enclosure, regardless of the arc origination location
  • Up to four-high breaker configuration with no additional layout restrictions
  • Strengthened side and rear panels with standard split rear covers for cable access
  • NEMAT 1 enclosure, with either top or bottom cable or bus duct entry
  • Cable compartment floor plates

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Optional features
  • Zone selective interlocking protection
  • ANSI Type 2B arc-resistant design protects the operator even with the low voltage instrument compartment door open
  • Arcflash Reduction Maintenance SystemE
  • Safety shutters
  • One-piece hinged and bolted rear panel
  • Insulated bus
  • Vented bus/cable compartment barrier
  • Cable compartment segregation barrier

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Benefits
  • Superior protection against arcs in breaker, bus or cable compartments
  • No increase in footprint over regular Magnum DS switchgear
  • Closed door racking
Standards
  • UL 1558 and UL 891
  • ANSI C37.20.1, ANSI C37.13, ANSI C37.51 and ANSI C37.20.7
  • CSAT standard—CSA C22.2 No. 31-04
  • Third-party (UL/CSA) witness tested
  • Seismic certification 2006-IBC
Testing

Testing procedures were completed per ANSI C37.20.7 standards with arcs initiated in:

  • Breaker compartment
  • Vertical and horizontal bus
  • Cable termination compartments

Additionally, the tested arc duration was up to the full 0.5 seconds recommended by ANSI C37.20.7, with no dependence on the tripping speed of an upstream breaker.
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Acti 9 - The Fifth Generation Of Modular Systems

Acti 9 - The Fifth Generation Of Modular Systems

Acti 9 represents the fifth generation of Schneider’s low voltage modular systems. His older brother Multi 9 has finally evolved to much better and smarter system. Multi 9 was the famous and most known product of Schneider’s ex brand Merlin Gerin (now is incorporated into Schneider global brand), and now new Acti 9 is ready to inherit it.

Before Acti 9 – iC60 and Multi 9 – C60 modular systems, there was also Multi 9 – C32, F32 and F70 at the beginning of development.

Acti 9 covers all applications, especially in polluted environments and networks, for absolute safety and improved continuity of service.

Acti 9 exclusivities

For absolute safety and improved continuity of service.

  • VISI-SAFE – Guaranteed safe intervention on site
  • VISI-TRIP – Fast location of the faulty outgoer to minimize dowtime
  • The super immunization “Si” on RCD – Improved continuity of service, especially in polluted environments and networks
  • Front face class 2 - Continuous safety for operators and non-qualified personnel

Acti 9 exclusivities

VISI-SAFE concept is combining:

  • Contact position indication with the green strip
  • Impulse voltage withstand: Uimp 6 kV
  • Insulation voltage: Ui 500 V
  • Pollution degree: level 3 (conductive pollution, dust,etc.)

Easy to choose

  • Compliance with both IEC/EN 60898 & IEC/EN 60947-2 - Suitable for commercial and industrial applications
  • RCDs fully coordinated up to the MCB’s breaking capacity – Peace of mind, easy to select
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Easy to install

  • Quick and ergonomic wiring, safe connections
    - IP20 insulated flap terminals
    - Distribloc system
  • Twice the standard terminal tightening torque
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Easy to operate

  • Great readability:
    - large circuit labelling area
    - specific colour code system.
  • Upgradeability with Multiclip system
  • Load rebalancing and addition of new outgoers.
  • Device removable with comb busbar in place
  • Double locking.

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AKD-20 low-voltage switchgear continues the tradition of the AKD switchgear line while delivering enhanced arc flash protection. Built to ANSI standards, its protection features include non-vented panels plus insulated and isolated bus, and it integrates our new state-of-the-art EntelliGuard® breaker-trip unit system. It also features an optimized footprint so that it now fits into a smaller area for the most common configurations.

EntelliGuard® G circuit breakers are the newest line of GE low-voltage circuit breakers, the next step in the evolution of a line known for its exceptional designs and performance. They are available from 800A to 5000A, with fault interruption ratings up to 150kAIC – without fuses.

Integral to the EntelliGuard G line are the new, state-of-the-art EntelliGuard TU Trip Units, which provide superior system protection, system reliability, monitoring and communications. The breaker-trip unit system delivers superior circuit protection without compromising either selectivity or arc flash protection. The EntelliGuard breaker-trip unit system demonstrates yet again GE’s core competencies in reliable electric power distribution, circuit protection and personnel protection. AKD-20 includes many features that address the needs of system reliability, arc flash protection and reduced footprint size.

Features and Benefits

  • The optimized footprint uses smaller section sizes when possible. Sections are provided in 22″, 30″ or 38″ widths.
  • Breaker compartment doors have no ventilation openings, thus protecting operators from hot ionized gases vented by the breaker during circuit interruption.
  • A superior bus system offers different levels of protection.  Insulated and isolated bus makes maintenance procedures touch friendly to reduce the risk of arc flash.
  • True closed-door drawout construction is standard with all AKD-20 equipment. The breaker compartment doors remain stationary and closed while the breaker is racked out from the connect position, through test, to the disconnect position. Doors are secured with rugged 1/4-turn latches.
  • An easy-to-read metal instrument panel above each circuit breaker holds a variety of control circuit devices, including the RELT switch.
  • Each circuit breaker is located in a completely enclosed ventilated compartment with grounded steel barriers to minimize the possibility of fault communication between compartments.
  • Optional safety shutters protect operators from accidental contact with live conductors when the breaker is withdrawn.
  • Easy access to equipment compartments simplifies maintenance of the breaker cubicle and control circuit elements as well as inspection of the bolted bus connections.
  • The conduit entrance area meets NEC requirements.  Extended depth frame options are available in 7″ and 14“ sizes for applications requiring additional cable space. The section width also can be increased for additional cable space.
  • A rail-mounted hoist on top of the switchgear provides the means for installing and removing breakers from the equipment. This is a standard feature on NEMA 3R outdoor walk-in construction and optional on indoor construction.
  • Control wires run between compartments in steel riser channels. Customer terminal blocks are located in metal-enclosed wire troughs in the rear cable area. Intercubicle wiring is run in a wireway on top of the switchgear, where interconnection terminal blocks are located.
  • All EntelliGuard G circuit breakers are equipped with rollers and a guidebar to provide easy and accurate drawout operation.
  • An optional remote racking device reduces the risk of the arc flash hazard by allowing the operator or electrician to move the breaker anywhere between the DISCONNECT and CONNECT positions from outside the arc flash boundary.
  • Optional infrared (IR) scanning windows can be installed in the switchgear rear covers to facilitate the use of IR cameras for thermally scanning cable terminations.
  • AKD-20 switchgear can be expanded easily to handle increased loading and system changes. Specify a requirement for a fully equipped future breaker to obtain a cubicle that has been set up for additional breaker installation, or add vertical sections without modifications or the use of transition sections.
  • An array of safety interlock and padlocking features are available to accommodate any type of lockout-tagout procedure a customer may have.
  • Optional Power Management:  With the proper devices and GE Enervista Power Management Control System (PMCS), facility power can be tracked and controlled.
  • Optional Metering and Power Quality:  The latest high technology EPM devices are available for the AKD-20 with broad capabilities for usage monitoring, cost allocation, load monitoring, demand tracking, common couplings with utilities, load and process control, and power quality monitoring.

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Siemens TechTopic | Bus Joint Fundamentals

Siemens TechTopic | Bus Joint Fundamentals

Proper design of bus bar joints is a necessity for long equipment life. The objectives that a good bolted bus bar joint must fulfill include:

• It must provide good conductivity, so that the bus system will meet the temperature rise requirements in the ANSI standards.

• It must withstand thermal cycling, so that the low resistance joint will be maintained for the life of the equipment.

• The joint pressure should be high (for good conductivity), but not so high that cold flow of the bus material occurs, which would cause the joint to deteriorate with time.

•The joint should have good resistance to corrosion in normal installation environments.

• It must be able to withstand the mechanical forces and thermal stresses associated with short-circuit conditions.

Figure 1: Anatomy of a bolted bus bar joint

Figure 1: Anatomy of a bolted bus bar joint

Figure 1 shows a bolted bus bar joint, simplified to show two bus bars connected using a single bolt. Except in rare situations, the bus bars are silver plated (standard) or tin plated (optional), to improve the resistance to corrosion. The bolt is a high strength grade 5 cap screw, while the nut is a grade 2 (heavy wall) nut. The joint includes a large diameter, thick flat washer on both sides of the joint, adjacent to the bus bars. A split lock washer is installed under the nut to assure that the joint stays tight over the life of the equipment.

Why do we use a grade 2 nut with a grade 5 bolt? The grade 2 nut is more ductile than the grade 5 bolt, so that when the nut is torqued in place, the threads in the nut will tend to be swaged down and burnished to a degree, which results in a more equal distribution of load on all threads. This spreads the force more evenly and avoids unacceptable stress levels in the bolt and the nut.

Some users request that special non-magnetic hardware be used in bus joints. Historically, particularly in open bus systems exposed to the weather, difficulties were encountered with corrosion, and this may be one reason that some still ask for non-magnetic hardware. Others prefer non-magnetic hardware because of the perception that it results in a lower temperature rise. While these reasons may have had merit decades ago, we feel they are unnecessary today. Non-magnetic hardware (usually stainless steel or silicon bronze) is expensive and difficult to obtain. In addition, the tensile strength and yield strength of non-magnetic hardware is lower than that of high strength steel, so that tightening torques will generally be lower with the special hardware. The net effect of lower torque and pressure may very well counterbalance any slight temperature rise benefit associated with non-magnetic hardware.

We also specify that the flat washers are to have larger diameter and greater thickness than standard washers. The purpose of the washers is to distribute the clamping force of the bolts over a wider area. To accomplish this, we need a washer that is relatively rigid, with a larger diameter than would be normal for the size bolt used. If a normal small diameter, thin washer (or worse, none at all) is used, the joint will deteriorate over time because of cold flow of copper from the high pressure region directly under the bolt head (or the nut).
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Figure 2: Distribution of forces in a bolted bus bar joint

Figure 2: Distribution of forces in a bolted bus bar joint

Figure 2 shows the distribution of forces in a bolted bus bar joint. To obtain a low resistance bus bar joint, we must establish and maintain sufficient pressure, and distribute the pressure over a large area. Initially, the two bus bars mate at only a few peaks or high spots. As the bolt is tightened, the bus conductors begin to deform, bringing more of these peaks into contact. At the design pressure, there is a relatively larger contact area, so that there are a multitude of parallel electrical connections between the bars.

As shown in figure 2, the force is concentrated more heavily around the bolt hole. Since the pressure is highest in the vicinity of the bolt hole, the surface irregularities in this area are flattened out as the mating surfaces are forced into more intimate contact. The joint resistance in this area will be lower than elsewhere in the joint. As distance from the bolt hole increases, pressure decreases and joint resistance increases. Beyond the area defined by the washer, pressure decreases rapidly and little effective current carrying capacity results.

From figure 2, we can see how the large diameter washers serve to distribute the clamping force more uniformly over a wider area than would be the case with a smaller washer, or none at all.

A properly designed bolted bus bar joint will allow the bus system to meet the temperature rise limits imposed by the ANSI standards, and will also have the thermal and mechanical capability to withstand the heat generated and forces imposed under the worst case short-circuit conditions.

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SOURCE: T. W. (Ted) Olsen – Manager, Technology | Siemens Power Transmission & Distribution, Inc.

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Guide To Low Voltage Busbar Trunking Systems

Guide To Low Voltage Busbar Trunking Systems

Modern electrical desdign and installations are often placing increasing demands on all products of the electrical equipment manufacturer.

Products must have:

• Reliable service life
• Adaptability to new requirements
• Low installation costs
• Low maintenance costs
• Inherent safety features
• Minimal purchase cost
• Energy efficiency

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In today’s market one of the most important elements is cost effectiveness. In an electrical installation, one area where savings can be made and provide the features listed above is in the use of busbar trunking systems. Busbar trunking installations can be categorised into two basic types:

  • Distribution
  • Feeder

Distribution Feeder

This is the most common use of busbar trunking and is applied to distribute power over a predetermined area.    Busbar trunking can be run vertically or horizontally, or a combination of both. Typical applications would be:

  • Supply to large numbers of light fittings
  • Power distribution around factories and offices
  • Rising main in office blocks or apartment blocks to supply distribution boards serving individual floors.

Power is taken from busbar trunking by the use of tap off units which connect at defined positions along the busbar trunking, and allow power to be taken from the system, usually via a suitable protective device.

Advantages over cable:

  • The contractor can achieve savings with respect to material i.e. cable trays and multiple fixings and also labour costs associated with multiple runs of cable.
  • Reduced installation time since busbar trunking requires less fixings per metre run than cable.
  • Multiple tap-off outlets allow flexibility to accommodate changes in power requirements subsequent to the initial installation (subject to the rating of the busbar trunking).
  • Repositioning of distribution outlets is simpler
  • System is easily extendable.
  • Engineered product with proven performance.
  • Type tested to recognised international and national standards.
  • Aesthetically pleasing in areas of high visibility.

Feeder Trunking

When used for the interconnection between switchboards or switchboard and transformer, busbar trunking systems are more economical to use, particularly for the higher current ratings, where multiple single core cables are used to achieve the current rating and compliance with voltage drop and voltage dip requirements.

Beside this, bunch of cables are increasing possiblity of heating between cables and eventually short circuit.

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Advantages over cable:

  • Greater mechanical strength over long runs with minimal fixings resulting in shorter installation times.
  • Replaces multiple runs of cable with their associated supporting metalwork.
  • Easier to install compared to multiples of large cables with all of the associated handling problems.
  • Less termination space required in switchboards.
  • Type tested short circuit fault ratings.
  • Takes up less overall space, bends and offsets can be installed in a much smaller area than the equivalent cable space.
  • Cable jointer not required.
  • Busbar trunking systems may be dismantled and re-used in other areas
  • Busbar trunking systems provide a better resistance to the spread of fire.
  • Voltage drop and voltage dip in the majority of cases is lower than the equivalent cable arrangement.

Typical Busbar Layout
Typical Busbar Layout

Tap-Off Units

Tap-off units are of two types, either plug-in or fixed. Plug-in units are designed to be accommodated at tap-off outlets at intervals along the distribution busbar trunking. Fixed tap-off outlets are engineered and positioned during manufacture to suit the specified installation. The tap-off unit usually contains the device providing protection to the outgoing circuit terminated at the unit to distribute power to the required load.

There are various types of protective devices, for example:

1. HRC fuses to BS EN 60269-1 (BS88)
2. Miniature Circuit Breakers to BS EN 60898
3. Moulded Case Circuit Breakers to BS EN 60947-2

HRC fuses may be incorporated into fuse combination units to BS EN 60947-3. The degree of enclosure protection of the tap-off unit is defined by BS EN 60529.

Each tap-off unit contains the necessary safety features for systems and personnel protection, as follows:

  • Plug-in units are arranged to be non-reversible to ensure that they can only be connected to give the correct phase rotation.
  • Plug-in units are arranged to connect the protective circuit before the live conductors during installation and disconnect the protective circuit after the live conductors while being removed.
  • Where units are provided with a switch disconnector or circuit-breaker these are capable of being locked in the OFF position.
  • Covers permitting access to live parts can only be removed by the use of a tool and will have any internally exposed live parts shielded to a minimum of IP2X or IPXXB in accordance with BS EN 60529.
  • Outgoing connection is achieved by cable terminations in the unit or by socket outlets to BS EN 60309-2 or BS 1363.

Fire Stops

Recommendations for the construction of fire-stops and barriers where trunking penetrates walls and floors classified as fire barriers. Internally the trunking may or may not require fire-stop measures according to the construction; where they are required these will generally be factory-fitted by the manufacturer and positioned according to a schematic drawing for the installation. Compact or sandwich-type trunking does not require internal fire-barriers, as suitability as a fire-barrier is inherent in the design.

However in all cases verification of the performance of the trunking under fire conditions needs to be provided by the manufacturer.

The following information is provided for guidance, and the method used should be agreed with the trunking manufacturer. It is not the responsibility of the trunking manufacturer to provide the specification or detail the rating or construction of the fire-stop external to the trunking.

Protective Earth Condustor Sizes

The sealing external to the busbar trunking (with or without an internal fire barrier) will need to conform to applicable building regulations. This may require filling the aperture around the busbar trunking with material to maintain the same fire proofing as the wall or floor.
Careful consideration needs to be given to the access required to complete the fire- stop. It may be necessary to install sections of fire-stop at the stage of installation of the trunking if access afterwards is impossible e.g. trunking runs in close proximity.

The protective earth connection(s) to the busbar trunking system shall conform to Section 543-01 of BS 7671 (IEE Wiring Regulations Sixteenth Edition).

Low-Noise Earth Systems

A low-noise earth, commonly referred to as a ‘clean earth’, is typically specified when electronic apparatus supplied from the system is sensitive to spurious voltages arising on the system earth. This is particularly true with IT equipment, found in all commercial premises these days, where data processing functions can be corrupted.

The low-noise earth is provided by a conductor separated from the protective earth (PE) and from all extraneous earth paths throughout the distribution system.
Many busbar trunking systems provide a ‘clean earth’ conductor in addition to the three phase conductors plus neutral, using the case or an external conductor as PE.

Tap-off units must be specified as ‘clean earth’ for the circuits concerned since the separation of the earths must be maintained and an additional termination will be provided for the load circuit ‘clean earth’ conductor. Sizing of the ‘clean earth’ conductor is not specified in BS 7671 (IEE Wiring Regulations Sixteenth Edition) but the usual practice is to calculate the size in the same way as for the protective earth conductor.

Neutral Sizes/Harmonics

The designer of the electrical network specifies the size of the neutral conductor depending upon the network loading. Typically this tends to be a neutral conductor the same size as the phase conductors (i.e.100% neutral).    As a minimum a 50% neutral may be specified.

The BS 7671 (IEE Wiring Regulations Sixteenth Edition) states “In a discharge lighting circuit and polyphase circuits where the harmonic content of the phase currents is greater than 10% of the fundamental current, the neutral conductor shall have a cross-sectional area not less than that of the phase conductor(s).”

With the increase of non-linear (almost anything electronic) single phase loads connected to a network, for example electronic ballasts in lighting fittings, or switch-mode power supplies (the type found in personal computers and servers) the total harmonic distortion is increased.

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Busbar Technical Specification

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:

RT 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

    Rx 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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    Xf = x F/50
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    where Xf is the reactance at frequency F in Hz

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Source: Siemens Barduct Busbar Specification

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Maintenance Of Low Voltage Circuit Breakers

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

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Maintenance Of Molded Case Circuit Breakers (MCCB)

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

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Short Circuit Parameters in Low Voltage AC Circuits

Low-voltage equipment standards IEC60947 and IEC60439 currently include short-circuit ratings for products and assemblies respectively, defined in terms of the ability of the equipment to operate at a level of peak current, an RMS current for a specified time and/or a level of current conditional upon a short-circuit protective device in series. In practice the correct application of the various short-circuit ratings needs to be fully understood by the circuit designer to avoid leaving a circuit or equipment with inadequate short-circuit protection. It is also useful to take full advantage of the capability of devices and systems to avoid over-engineering, with the consequent unnecessary additional cost. This guide does not concern itself with the issue of selectivity between devices in series, which must be considered separately.

Principles of Application

The Installation

In order to ensure the capability of equipment under short-circuits conditions the circuit designer must firstly have available the prospective fault level at the point of installation of each item of equipment. This is produced by a system protection study. IEC60781 provides an application guide for calculation of short-circuit currents in lowvoltage radial systems. Short-circuit parameters are defined by this guide in terms, which include the following:

  • Prospective (available) short-circuit current:
    The current that would flow if the short-circuit were replaced by an ideal connection of negligible impedance without any change of the supply.
  • Peak short-circuit current Ip
    The maximum possible instantaneous value of the prospective (available) short-circuit current.
  • Symmetrical short-circuit breaking current Ib
    The r.m.s. value of an integral cycle of the symmetrical a.c. component of the prospective (available) shortcircuit current at the instant of contact separation of the first pole of a switching device.
  • Steady-state short-circuit current Ik
    The r.m.s. value of the short-circuit current which remains after the decay of the transient phenomena.
    - unlimited
    - limited by an SCPD (short-circuit protective device)
LV Assemblies (switchboard, distribution board etc.)

An assembly will have a short-circuit rating, assigned by the manufacturer, defined in terms of the maximum prospective fault level applicable at the point it is connected into the system.

This will have been determined by test and/or design calculations as specified in the assembly standard, IEC60439-1, or applicable part thereof.

The terminology to define the short-circuit rating of an assembly is given in the standard as follows:

  • Rated short-time current (Icw) (of a circuit of an assembly)
    Summarised as: The r.m.s value of short-time current that a circuit of an assembly can carry without damage under specified test conditions, defined in terms of a current and time e.g. 20kA, 0,2s.
  • Rated peak withstand current (Ipk) (of a circuit of an assembly)
    Summarised as: The value of peak current that a circuit can withstand satisfactorily under specified test conditions.
  • Rated conditional short-circuit current (Icc) (of a circuit of an assembly)
    Summarised as: The value of prospective short-circuit current that a circuit, protected by a specified shortcircuit protective device (SCPD), can withstand satisfactorily for the operating time of that device, under specified test conditions. Note: the short-circuit protective device may form an integral part of the assembly or may be a separate unit.An assembly may be assigned a value of Icc alone.

- An assembly may be assigned values of Icw and Ipk (but cannot be assigned a value of Icw or Ipk alone).
- An assembly may be assigned values of Icw, Ipk and Icc.
- An assembly may be assigned different values of Icc for different circuit protective devices and/or system voltages.
- An assembly may be assigned different values of Icw for different short-time periods e.g. 0.2s, 1s, 3 s.

Switchgear

In terms of short-circuit capability switchgear must be considered in respect of it’s function in the particular application. A switching device is considered in two respects, self-protection and use as a short-circuit protective device (SCPD) where applicable.

Switchgear – Self Protection Against Short Circuit

Two cases are considered:

  • Load and overload switching alone, without any short-circuit switching capability:
    In this case the switching device will be short-circuit rated on a similar basis to a circuit of an assembly (see above), with a rating of Icw and/or a conditional short-circuit rating, but will in addition have a rated short-circuit making capacity Icm.
  • Load, overload and short-circuit switching capability:
    • Fused switchgear – in this case the short-circuit breaking function is provided by the integral fuses and the device will have a conditional short-circuit rating
    • Circuit breakers – the circuit-breaker will be self-protecting up to its breaking capacity rating (see later). At fault levels above the breaking capacity rating a circuit-breaker may be capable of operating with ‘back-up’ protection by an SCPD (this is in effect a conditional rating, but the term is not generally used in this context).
Switchgear – Application as SCPD
  • Fused Switchgear and Fuses as SCPD
    Since the short-circuit breaking function in fused switchgear is provided by the fuses it is the fuse characteristics that are considered. These are given in IEC60269-1 as follows:

    • Breaking capacity of a fuselink
      - value (for a.c. the r.m.s. value of the a.c. component) of prospective current that a fuselink is capable of breaking at a stated voltage under prescribed conditions.
    • Cut-off current
      Summarised as: maximum instantaneous value reached by the current during the breaking operation of a fuselink when it operates to prevent the current reaching the prospective peak.
    • Operating I²t (Joule integral)
      Summarised as: Integral of the square of the current over the operating time of the fuse.
      Sometimes referred to as ‘energy let-through’. When expressed in A²t gives the energy dissipated per ohm and thus represents the thermal effect on the circuit.
  • Circuit-breakers as SCPD
    • Moulded-case circuit-breakers (MCCBs) and air circuit-breakers (ACBs) are rated according to IEC60947-2 as follows
      • Rated short-circuit making capacity (Icm)
        Summarised as: The maximum peak prospective current that the circuit-breaker can make on to satisfactorily.
    • Rated short-circuit breaking capacities:
      • Rated ultimate short-circuit breaking capacity (Icu)
        Summarised as: The r.m.s prospective current that the circuit breaker is capable of breaking at a specified voltage under defined test conditions, which include one break and one make/break operations.
      • Rated service short-circuit breaking capacity (Ics)
        Summarised as: The r.m.s prospective current that the circuit breaker is capable of breaking at a specified voltage under defined test conditions, which include one break and two make/break operations. The standard specifies fixed relationships to Icu of 25, 50, 75 or 100%.
      • Rated short-time withstand current (Icw)
        Summarised as: The r.m.s value of short-time current assigned by the manufacturer based on specified test conditions. Minimum values are given in the standard.

A circuit-breaker can only be assigned a rated short-time withstand current Icw if it is equipped with a time-delay overcurrent release.

All circuit-breakers to IEC60947-2 will have values of Icu and Ics.

Characteristics of circuit-breakers not mandated in IEC60947-2 but having application to short-circuit protection:

  • Cut-off current
    The maximum instantaneous value reached by the current during the breaking operation of a circuit-breaker when it operates to prevent the current reaching the prospective peak.
  • Operating I²t (Joule integral)
    Integral of the square of the current over the operating time of the circuit-breaker on a short-circuit. Sometimes referred to as ‘energy let-through’. When expressed in A²t gives the energy dissipated per ohm and thus represents the thermal effect on the circuit.

Examples of the Practical Application of the Product Characteristics

In simple studies only the r.m.s value of steady-state short-circuit current (Ik) is quoted. The peak current is assumed to be in a standard relationship to the r.m.s current, determined by the overall power factor, and taken into account in the rating of SCPDs to the respective IEC standards.

Circuit Protection

The application of short-circuit protective devices (SCPD) to circuit protection i.e. the protection of cables, is detailed in the installation rules, IEC364. In general it is accepted that selection of the protective device on the basis of thermal protection of a cable automatically provides short-circuit protection up to the breaking capacity of the SCPD, in the case of non-time-delayed devices.

Short-Circuit Protection for LV assemblies
Switchboard/Motor-Control Centre

The prospective short-circuit current at the input to the switchboard is obtained from a system protection study.
This will be given as an r.m.s value.

  • If the switchboard has an Icw current value higher than the prospective current level then the only requirement is to limit the time for which a short-circuit could persist to within the short-time value. This is achieved by the setting of releases upstream or at the incomer to the switchboard.
  • If the switchboard has an Icc rating higher than the prospective current level then the only requirement is to include the specified SCPD in the circuit. This may be added in the circuit upstream or may already be included as an incomer to the switchboard.
Busbar Trunking (BBT)

The prospective short-circuit current at the input to the switchboard is obtained from a system protection study.
This will be given as an r.m.s value.

  • If the BBT has an Icw current value higher than the prospective short circuit current level then the only requirement is to limit the time for which a short-circuit could persist to within the short-time value. This is achieved by the time-delay setting of overcurrent releases upstream.
  • If the BBT has an Icw lower than the prospective short circuit current level Ik but has an Icc rating higher than Ik then the only requirement is to include the specified SCPD in the circuit upstream or in the end-feed unit. The suitability of any given SCPD may be derived from the cut-off current and Joule-integral characteristics by comparison with proof-test parameters.
Motor Control Gear (MCG)

Motor starters and contactors are not generally self-protecting against the effects of short-circuit and therefore need to be associated with an SCPD. In this particular case test procedures to IEC60947-4-1 recognise the difficulty of protecting sensitive devices from damage under heavy short-circuit conditions. Thus a special case of conditional rating is obtained which allows two classes of co-ordination with an SCPD:

Type 1 – in which a certain amount of damage to the MCG is accepted.
Type 2 – in which the MCG is capable of further use.

These ratings can only be obtained by type-testing and thus the data must be obtained from the manufacturer of the SCPD or the MCG.

Miniature Circuit Breakers (MCBs)

When applied in other than domestic (household) situations the short-circuit capability of MCBs to IEC60898 is often inadequate and they need to be ‘backed-up’ by another SCPD. Details of how the appropriate SCPD is determined are given, for circuit-breakers, in Appendix A of IEC60947-2. Basically this shows that only testing of the required combination is satisfactory and thus the data must be obtained from the manufacturer of the SCPD or the MCB. The same applies to fuses used as SCPD.

Izvor: www.voltimum.co.uk

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Works with many PLCs: Allen-Bradley, Schneider, Siemens, Omron...

Works with many PLCs: Allen-Bradley, Schneider, Siemens, Omron...

This software helps you troubleshoot problems in your PLC logic or equipment through easy data acquistation and analysis of time dependent behaviour. It is espcially well suited for Siemens Simatic S5 and S7 PLC applications.

PLC-ANALYZER pro 5 is a software system for logic analysis and acquisition of recorded data on PLC-controlled facilities. Acquisition, representation, and evaluation of PLC signals such as inputs, outputs, flags, data words, etc. is now very easy.

Online display makes possible observation of the signal waveform in real time. In addition to long-term recording, trigger conditions can be specified for the acquisition of particular events. This allows rarely occurring sporadic errors to be recorded for later analysis.

In contrast to traditional logic analyzers, the PLC-ANALYZER pro 5 has the decisive advantage of recording process data through standardized PLC interfaces.

The program e. g. supports MPI/PPI, PROFIBUS and TCP/IP Ethernet for SIMATIC S7 or the programming unit interface for SIMATIC S5.

A computer that is connected for the purpose of programming the PLC can be used for recording process data without hardware modifications. The tiresome process of hooking up monitoring cables is now a thing of the past.

Cycle-precise recording is attractive because of the complete acquisition of measured values in each PLC cycle. By using the measurement interface AD_USB-Box external voltage and current signals, which are not available in the PLC, can also be recorded. Project files make it possible to automate frequently recurring acquisition sessions for various facilities.

The PLC-Analyzer pro 5 is well suited for the following applications:

* Failure diagnosis for PLC systems
* Finding and localizing sporadic errors
* Analysis and optimization, cycle time reduction
* Long-term recording of measured values
* Documentation and support of QA, + TPM/OEE
* Installation, maintenance, construction and education

The software works with many PLCs including Allen-Bradley, Schneider Electric, Siemens and others. Its capabilities can also be expanded by an optional box for recording data variables external to the PLC, and also an additonal solution for longer term historical recording.

List of available PLC drivers for PLC-ANALYZER pro 5:

PLCInterfaceRemarkManual
Siemens SIMATIC S7MPI/PPI, PROFIBUScycle precise (also suitable for
SIMATIC C7, M7, SINUMERIK (S7), SAIA xx7, VIPA S7 and
S7-PLCSIM)
Download 3 MB*
Siemens SIMATIC S7Ethernet TCP/IP, PROFINETcycle precise (also suitable for
SIMATIC C7, M7, SINUMERIK (S7), SAIA xx7, VIPA S7 and
S7-PLCSIM)
Download 3 MB*
Siemens SIMATIC S5programming interfacecycle preciseDownload 3 MB*
Ethernet TCP/IPDownload 674 KB
Siemens LOGO!programming interfaceDownload 650 KB
Siemens SINUMERIK (S5)programming interfacecycle preciseDownload 3 MB*
Siemens SIMOTION C/P/DMPI / PROFIBUS / Ethernet TCP/IPservo-cycle preciseDownload 629 KB
BOSCH CLprogramming interface (BUEP 19E)Download 574 KB
CoDeSysEthernet TCP/IPfor CoDeSys based systemsDownload 759 KB
PILZ PSSprogramming interfaceDownload 569 KB
PILZ PSSEthernet TCP/IPDownload 598 KB
PHOENIX ILCEthernet TCP/IPDownload 603 KB
Jetter JetControl / Delta / Nanoserial / Jetway / PC-PPLCDownload 716 KB
Jetter JetControlEthernet TCP/IPDownload 716 KB
B&REthernet TCP/IP / serialDownload 689 KB
Allen-Bradley ControlLogix / PLC / SLCRS232 / DH+ / DH-485Download 605 KB
Allen-Bradley ControlLogix / PLC / SLCEthernet TCP/IPDownload 605 KB
GE Fanuc Series 90 / VersaMax / Nano / Microprogramming interface (SNP)Download 573 KB
GE Fanuc CNC/PMCEthernet TCP/IP / HSSB
HITACHI H / EH-150 / Micro-EHprogramming interfaceDownload 588 KB
HITACHI H / EH-150 / Micro-EHEthernet TCP/IPDownload 588 KB
MITSUBISHI MELSEC Q / A / FXprogramming interfaceDownload 616 KB
MITSUBISHI MELSEC Q / AEthernet TCP/IPDownload 576 KB
Schneider Modicon TSX Quantum / Momentum / CompactModbus PlusDownload 580 KB
Modbus IDownload 565 KB
Schneider Modicon TSX Quantum / Momentum / CompactModbus TCP/IPDownload 569 KB
Schneider Modicon TSX Premium / Atrium / Micro / NanoTCP/IP / Uni-TelwayDownload 569 KB
Schneider AEG TSX A250 / A120 / Microprogramming interface (KS)Download 562 KB
OMRON C / CV / CS1programming interface (Host Link)Download 571 KB
Beckhoff TwinCAT I/Orecording of TwinCAT I/O-variablesDownload 656 KB
AUTEM AD_USB-BoxUSB-Portrecording of external voltage and current signalsDownload 296 KB
Downloads

Take a look for details on AUTEM website.

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Compact NSX – prekidač nove generacije

Compact NSX 100A–630A | prekidač nove generacije

Stari Compact NS (100A-630A) definitivno odlazi u penziju, pošto je dugo bio prisutan na tržištu kao jedan od najpouzdanijih prekidača. Zameniće ga mlađi brat Compact NSX, moderan prekidač sa daleko više funkcija i mogućnosti, koji dugo neće imati konkurenciju na polju prekidača do 630A sa mogućnostima kao što su mikroprocesorska zaštita, komunikacija, vizuelni displej, daljinski monitoring energije i snage itd. Budući da je konkurencija na polju izuzetno jaka (ABB, Siemens…), Schneider Electric nije gubio vreme i razvio je ovaj prekidač nove generacije. Budući da cena skoro uvek igra presudnu ulogu kod odlučivanja Investitora ili Panel Builder-a koji tip prekidača koji će se naći u razvodnom ormanu – cena Compact NSX prekidača je čak i niža od starog Compact NS. Odnos cena/kvalitet je kod NSX-a značajno veći nego kod starog NS-a.

Nova mogućnost praćenja potrošnje električne energije kod malih potrošača pojedinačno, pruža detaljnu analizu energetske efikasnosti, kao i mogućnost velike uštede i energije i finansijskih sredstava.

Karakteristike prekidača Compact NSX

  • Nazivna struja: 16 do 630 A
  • 6 nivoa prekidnih moći 25 do 150 kA na 415 V (pogledaj detaljnije)
  • Nazivni napon: do 690 V
  • 2 veličine kućišta za ceo opseg 16 do 630 A
  • Verzija sa 3 i 4 pola
  • Fiksna i izvlačiva izvedba
  • Rastavljanje sa pozitivnom indikacijom prekida
  • Širok opseg zaštitnih jedinica: termomagnetna, elektronska, mikroprocesorska zaštita
  • Diferencijalna zaštita pomoću dodatnih Vigi modula
  • Merenje osnovnih električnih parametara: I, U, P, E, THD, f, CosF
  • Širok opseg pomoćnog pribora i dodataka koji se mogu ugrađivati na samom mestu ugradnje
  • Plug and Play sistem ožičenja komunikacije kao i opseg dodatnih opcija (eksterni displej, modul za održavanje…)
  • Usaglašenost sa medjunarodnim standardima: IEC 60947-1 i 2, Nema, IEC 68230 za klasu tropikalizacije 2
  • Usklađenost za najzahtevnijim specifikacijama kompanija za klasifikaciju u brodogradnji:Bureau Veritas, Lloyd’s Register of Shipping, Det Norske Veritas, RINA.

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Kompaktni dizajn i vrlo jednostavna ugradnja mikroprocesorske jedinice MICROLOGIC.
(zarotiraj da vidiš!)
….

Primena prekidača Compact NSX:

  • Standardne aplikacije sa standardnim strujama kratkog spoja: zgradarstvo, industrijske zgrade i postrojenja, bolnice…
  • Primene koje zahtevaju visoke prekidne moći: procesna industrija, metalurgija
  • Posebno zahtevne aplikacije: brodogradnja
  • Specifične aplikacije: agresivne sredine, 400Hz, 16 2/3 Hz
  • Aplikacije kod kojih je obavezno merenje potrošnje električne energije svakog potrošača

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Eksterni displej FDM121 | Micrologic | Komunikacija

Eksterni displej FDM121 | Komunikacija

Kroz direktan pristup detaljnim informacijama, kao i umrežavanjem preko otvorenog protokola (Modbus), Compact NSX omogućava operaterima da optimizuju upravljanje svojim električnim instalacijama i sistemima. Compact NSX može da meri I, U, P, E, THD, f, CosF, zatim procesuira određene akcije, kao i da prikazuje važne podatke na više načina (na direktno ugrađenom ekranu, prednjem panelu ćelije razvodnog ormana sa FDM121, ili daljinski preko POWERLOGIC monitoring sistema – Scada sistema). Compact NSX ima specifične module za kontrolu motora koji omogućuju zaštitu od struje kratkog spoja, preopterećenja, faznog disbalansa i gubitka struje. U kombinaciji sa kontaktorom Schneider Electric-a, prekidač Compact NSX ispunjava sve uslove tipa 2 koordinacije (type 2 coordination) snage do 315kW na 415V prema IEC standardu 60947-4-1. Jedinice za okidanje (trip units) u Compact NSX-u su opremljene sa moment-limitiranim šrafovima i MITOP integrisanim uređajem za okidanje, koji dozvoljavaju da budu ugrađene tačno na svoje mesto u prekidaču. Jednom kada se nameste, električno testiranje više nije potrebno. Pre-ožičeni komunikacioni kablovi i “plug-and-play” interfejs omogućavaju jednostavnu i laku integraciju sa komunikacionim mrežama.

Korisnici mogu da prilagođavaju alarm za sve parametre , biraju prioritete koji će biti prikazani na displeju MICROLOGIC-a ili FDM121, kao i podešavaju vreme režima odlaganja akcije. Konstantno aktiviran zapis log-ova od svih događaja na prekidaču (log events) pružaju korisne informacije instalaterima nakon događaja (kratkog spoja, iznenadnog isključenja…).

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Dodatna oprema za fiksni prekidač Compact NSX
(stani mišem da vidiš!)

Korisni linkovi sa dokumentacijom za Compact NSX:

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Theory and examples of short circuit calculation

Theory and examples of short circuit calculation

An electrical transformer substation consist of a whole set of devices (conductors, measuring and control aparatus and electric machines) dedicated to transforming the voltage supplied by the medium voltage distribution grid (e.g. 12kV or 20kV), into voltage suitable for supplying low voltagelines wit power (400V-690V).

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Proračun pada napona

Proračun pada napona

Voltage drop is the reduction in voltage in an electrical circuit between the source and load. In electrical wiring national and local electrical codes may set guidelines for maximum voltage drop allowed in a circuit, to ensure reasonable efficiency of distribution and proper operation of electrical equipment (the maximum permitted voltage drop varies from one country to another)[1].

Voltage drop may be neglected when the impedance of the interconnecting conductors is small relative to the other components of the circuit.

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Book with graphical explanations of short circuit and its calculations (purpose, standards, types, calculations…)

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Unburied cables:

Cross sections

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1,646 views

What is cascading?

Cascading is the use of the current limiting capacity of circuit breakers at a given point to permit installation of lower-rated and therefore lower-cost circuit breakers downstream. The upstream circuit breakers acts as a barrier against short-circuit currents. In this way, downstream circuit breakers with lower breaking capacities than the prospective short-circuit (at their point of installation) operate under their normal breaking conditions. Since the current is limited throughout the circuit controlled by the limiting circuit breaker, ascading applies to all switchgear downstream. It is not restricted to two consecutive devices.

General use of cascadingcom

With cascading, the devices can be installed in different switchboards. Thus, in general, cascading refers to any combination of circuit breakers where a circuit breaker with a breaking capacity less than the prospective Isc at its point of installation can be used. Of course, the breaking capacity of the upstream circuit breaker must be greater than or equal to the prospective short-circuit current at its point of installation.
The combination of two circuit breakers in cascading configuration is covered by the following standards:

  • IEC 60947-2 (construction)
  • NF C 15-100, § 434.3.1 (installation)
Coordination between circuit breakers

The use of a protective device possessing a breaking capacity less than the prospective short-circuit current at its installation point is permitted as long as another device is installed upstream with at least the necessary breaking capacity. In this case, the characteristics of the two devices must be coordinated in such a way that the energy let through by the upstream device is not more than that which can be withstood by the downstream device and the cables protected by these devices without damage.
Cascading can only be checked by laboratory tests and the possible combinations can be specified only by the circuit breaker manufacturer.

Cascading and protection discrimination

In cascading configurations, due to the Roto-active breaking technique, discrimination is maintained and in some cases, even enhanced.

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ABB Oil Gas production Hand Book

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Canalis applicationsSchneider Electric u svojoj širokoj ponudi opreme za trafo stanice i objekte ima i oklopljeni šinski razvod “CANALIS” širokog dijapazona nazivnih struja, od 20A do 5000A. Za veće nazivne struje od 800A do 5000A koristi se Canalis oznake KT (postoje 2 verzije KTA i KTC). Skoro da nema projektanta koji nije čuo za Canalis, jer generalno u Srbiji investitori se odlučuju ili za kvalitetno tehničko rešenje sa Canalis-om, ili obično rešenje sa bakarnim sabirnicama. Šta je toliko specifično kod Canalis-a? Prvenstveno visoke perfomanse distribucije električne energije  i jednostavno prilagođavanje potrebama aplikacije, ali o tome više u nastavku posta. Schneider Electric je u toku prethodnih godina realizovao dosta značajnih projekata u kome je figurisao Canalis šinski razvod. Neki od najvećih projekata u Srbiji i Crnoj Gori:

UŠĆE SHOPPING CENTAR | DELTA CITY BGD | DELTA CITY PG | TELENOR BUILDING | VLASINSKE HE | DRENIK ND | TENT-B | KBC NOVI SAD | TS VEKTRA | TOPLANA KONJARNIK BGD
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Tehnički detalji KTA:

• 8 nazivnih struja od 800A do 4000 A.
• 4 aluminijumska provodnika sa istim poprečnim presekom (verzija 3L + N + PE).
• Provodnici izolovani poliesterskim filmom, klase B 130 °C, “halogen free”.
• Standardni stepen zaštite je IP55.
• Napon izolacije: 1000 V.
• Dostupni polariteti: 3L + PE, 3L + N +PE, 3L + N + PER (ojačan provodnik PE)
• Canalis KTA je veoma kompaktan i može biti postavljen pljoštimice, nasatice ili vertikalno. To znači da može biti montiran kroz spratni podest  ili protivpožarni zid bez ikakvog dodatnog protivpožarnog elementa. Standardnim rešenjem oklopljeni šinski razvod Canalis KTA  može da izdrži požar 2 sata, i to u skladu sa propisom ISO 834.

Kućište koje je u boji RAL 9001 obezbeđuje odličnu zaštitu i veoma jednostavno fiksiranje, a koristi se kao PE zaštitni provodnik (u skladu sa propisom NFC 15100 i IEC 60367). U verziji sa ojačanim zaštitnim provodnikom 3L + N + PER, praktično je dodat još jedan provodnik, tj. šina čiji je poprečni presek jednak polovini preseka faznog provodnika. Ova verzija Canalis-a ima lateralno ojačanje zbog velikih struja kratkih spojeva (Isc), što ima za posledicu i oko 25% veću težinu u odnosu na standardnu verziju.

TEHNIČKE KARAKTERISTIKE CANALIS-A: Klikni na sliku da vidiš uvećano

Vrednosti nominalnih struja u gornjoj tabeli se odnosi na KTA verziju Canalis-a. Vrednosti KTC Canalisa (bakarne sabirnice) su za stepen više, i poprečni presek im je manji.

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Gde se koristi Canalis KTA?

Osnovna namena je u trafo-stanicama za distribuciju el. energije od transformatora do niskonaponskog ormana, tj. dovodnog prekidača u njemu, zatim za dalju distribuciju od NN ormana do nekog podrazvodnog ormana (u TS ili u objektu), ili i za međuveze između sekcija u NN ormanu ili više njih. Što se tiče razvoda u objektu, može se koristiti vertikalni i horizontalni razvod sa mogućnošću postavljanja dovoljnog broja otcepnih kutija (osiguračima, rastavljačima ili prekidačima do 1000A) za dalje napajanje potrošača ili podrazvoda. Vertikalna trasa se fiksira pomoću specijalnih nosača-konzola koje imaju amortizere na sebi koji služe za ublažavanje eventualnih potresa usled dilatacije zgrade ili zemljotresa.

Canalis se može priključiti na bilo koji transformator, suvi ili uljni. Izvesnu prednost ima suvi transformator Schneider Electric-a – tip “TRIHAL“, koji oma mogućnost ugradnje dodatnog specijalnog priključka na Canalis (canalis interface), čime se sam spoj dodatno obezbeđuje i u električnom i mehaničkom smislu. Kod ostalih tipova (proizvođača) suvih transformatora postoji element “ruka” kojim se vrši priključenje na faze i nulu transformatora. Ovaj spoj Trihal-Canalis je već uveliko u upotrebi u puno trafo-stanica u Srbiji i Crnoj Gori, i investitori se uglavnom odlučuju na ovo rešenje zbog najveće pouzdanosti.
Što se tiče priključenja na niskonaponski orman, Canalis ima mogućnost priključenja na  bilo koji orman na bilo koje mesto! Šta to znači? Znači da se šinski razvod može prilagoditi zahtevima dispozicije u TS-i, ali i zahtevima projektanta. Najstandardnije rešenje priključka jeste sa gornje ili sa donje strane ormana. Za sve tipove ormana postoji univerzalni priključak koji se koristi u tu svrhu, ali i za priključenje na uljni transformator. Priključni element se kod NN ormana naslanja na krov ili dno ormana, i sa šinama priključuje na dovodne kontakte prekidača, ili na sabirnički sistem.

Schneider Electric kao i kod transformatora, nudi i kod niskonaponakih ormana predefinisani priključak na Canalis. U pitanju su razvodni ormani PRISMA P i kasetni razvod OKKEN. Prvi tip ormana se koristi kako u trafo-stanicama, tako i u objektu kao čisto razvodni ormani. Kod nas je veoma poznat i prihvaćen zbog svoje modularnosti i jednostavnosti montaže. OKKEN se za razliku od PRISMA P ormana koristi u “teškoj” industriji, kao i kod objekata gde ne sme biti prekida napajanja, i gde se ispad izvoda rešava brzom i jednostavnom zamenom kasete. No, malo sam se udaljio od osnovne teme… Ova dva tipa ormana imaju predefinisani priključak (canalis interfase) na Canalis koji nudi veoma dobre perfomanse spoja na dovodni prekidač (Masterpact). U najčešćem slučaju Canalis interface se montira u gornjem delu ormana iznad prekidača. U retkim slučajevima, Canalis interface se može okrenuti i “naopačke”, kada je potrebno da Canalis dođe sa donje strane.  Generalno gledano, Canalis interface je “najčistiji” način priključenja na Canalis sa najmanjim rizikom u električnom i mehaničkom smislu.

Može li se Canalis interface koristiti na drugim ormanima, koji nisu  proizvodnje Schneider Electric?? Naravno da može, ali drugi ormani nemaju gotove nosače interface-a kao Prisma P i OKKEN! No, to i nije neki problem da se napravi, svaki malo veštiji panel-builder se može snaći sa prilagođavanjem interface-a.

Radeći u Schneider Electric-u do sada sam imao dosta velikih kompleksnih projekata u kome sam projektovao oklopljeni šinski razvod Canalis, i moram priznati da se svaki projekat završio na veliko zadovoljstvo krajnjeg kupca, tj. investitora. Sam Canalis se inače projektuje u 3D programu u okviru AutoCAD-a, i potrebno je dosta truda i saradnje kako sa projektantom, tako i sa panel-builder-om koji proizvodi razvodne ormane na koji se priključuje Canalis, ali i sa izvođačem radova na objektu koji je u obavezi da montira Canalis.

Izvođeč radova dobija od mene iskotirane crteže sa svim detaljima. Schneider Electric uz oklopljeni šinski razvod Canalis uvek pruža i tehničku podršku izvođaču sa čime se ne može pohvaliti baš svaki proizvođač opreme.

Na kraju krajeva, ukoliko se investitor odluči da uloži više finansijskih sredstava u kvalitetnu distribuciju električne energije kroz svoj objekat i trafo-stanicu – ne može da pogreši. Na duži vremenski period usled posledica mogućih havarija zbog eventualnih kratkih spojeva ili ljudske greške, nema sumnje da je rešenje sa šinskim razvodom daleko ispred rešenja sa kablovima.

Naravno, skoro uvek, finansije daju svoju poslednju reč, mada se sve više investitora koji ulažu svoj novac na prostoru Srbije odlučuje upravo za kvalitet i pouzdanost opreme.

Edvard Csanyi
Schneider Electric Srbija

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