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KNX Architecture

KNX Architecture

Building Control technology as provided by KNX is a specialized form of automated process control, dedicated to the needs of home and building applications. One premise for KNX is to furnish a radically decentralized, distributed approach; hence the term network.
The KNX Device Network results from the formal merger of the 3 leading systems for Home and Building Automation (EIB, EHS, BatiBus) into the specification of the new KNX Association. The common specification of the “KNX” system provides, besides powerful runtime characteristics, an enhanced “toolkit” of services and mechanisms for network management.

On the KNX Device Network, all the devices come to life to form distributed applications in the true sense of the word. Even on the level of the applications themselves, tight interaction is possible, wherever there is a need or benefit. All march to the beat of powerful Interworking models with standardized Datapoint Types and “Functional Block” objects, modelling logical device channels.

The mainstay of S-(“System”) Mode is the centralized free binding and parameterisation (typically with the PC-based ETS tool). It is joined by E (“Easy”)-mode device profiles, which can be configured according to a structured binding principle, through simple manipulations – without the need for a PC tool. These configuration modes share common run-time Interworking, allowing the creation of a comprehensive and multi-domain home and building communication system.
The available Twisted Pair and Powerline communication media are completed with Radio Frequency (868 MHz band).
KNX explicitly encompasses a methodology and PC tools for Project Engineering, i.e. for linking a series of individual devices into a functioning installation, and integrating different KNX media and configuration modes. This is embodied in the vendor-independent Engineering Tool Software (ETS) suites for Windows.

Elements of the KNX Architecture

KNX specifies many mechanisms and ingredients to bring the network into operation, while enabling manufacturers to choose the most adapted configuration for their market. Figure 1 below shows an overview of the KNX model, bringing the emphasis on the various open choices. Rather than a formal protocol description, the following details the components or bricks that may be chosen to implement in the devices and other components a full operational system.

The KNX Model

As essential ingredients of KNX, we find in a rather top-down view.

  • Interworking and (Distributed) Application Models for the various tasks of Home and Building Automation; this is after all the main purpose of the system.
  • Schemes for Configuration and Management, to properly manage all resources on the network, and to permit the logical linking or binding of parts of a distributed application, which run in different nodes. KNX structures these in a comprehensive set of Configuration Modes.
  • Communication System, with a set of physical communication media, a message protocol and corresponding models for the communication stack in each node; this Communication System has to support all network communication requirements for the Configuration and Management of an installation, as well as to host Distributed Applications on it. This is typified by the KNX Common Kernel.
  • Concrete Device Models, summarized in Profiles for the effective realization and combination of the elements above when developing actual products or devices, which will be mounted and linked in an installation.

Applications, Interworking and Binding

Central to KNX’ application concepts is the idea of Datapoints: they represent the process and control variables in the system, as explained in the section Application Models. These Datapoints may be inputs, outputs, parameters, diagnostic data,…The standardized containers for these Datapoints are Group Objects and Interface Object Properties.

The Communication System and Protocol are expected to offer a reduced instruction set to read and write (set and get) Datapoint values: any further application semantics is mapped to the data format and the bindings, making KNX primarily “data driven”.
In order to achieve Interworking, the Datapoints have to implement Standardized Datapoint Types, themselves grouped into Functional Blocks. These Functional Blocks and Datapoint Types are related to applications fields, but some of them are of general use and named functions of common interest (such as date and time).

Datapoints may be accessed through unicast or multicast mechanisms, which decouple communication and application aspects and permits a smooth integration between implementation alternatives. The Interworking section below zooms in on these aspects. To logically link (the Datapoints of) applications across the network, KNX has three underlying binding schemes: one for free, one for structured and one for tagged binding. How these may be combined with various addressing mechanisms is described below.

Basic Configuration Schemes

Roughly speaking, there are two levels at which an installation has to be configured. First of all, there is the level of the network topology and the individual nodes or devices.
In a way, this first level is a precondition or “bootstrap” phase, prior to the configuration of the Distributed Applications, i.e. binding and parameter setting.
Configuration may be achieved through a combination of local manipulations on the devices (e.g. pushing a button, setting a codewheel, or using a locally connected configuration tool), and active Network Management communication over the bus (peer-to-peer as well as more centralized master- slave schemes are defined).
As described in the corresponding section below, a KNX Configuration Mode:

  • picks out a certain scheme for configuration and binding
  • maps it to a particular choice of address scheme
  • completes all this with a choice of management procedures and matching resource realizations.

Some modes require more active management over the bus, whereas some others are mainly oriented towards local configuration.

Network Management and Resources

To accommodate all active configuration needs of the system, and maintain unity in diversity, KNX is equipped with a powerful toolkit for network management. One can put these instruments to good use throughout the lifecycle of an installation: for initial set-up, for integration of multi-mode installations, for subsequent diagnostics and maintenance, as well as for later extension and reconfiguration. Network Management in KNX specifies a set of mechanisms to discover, set or retrieve configuration data actively via the network. It proposes Procedures (i.e. message sequences) to access values of the different network resources within the devices, as well as identifiers and formats for these resources – all of this in order to enable a proper Interworking of all KNX network devices. These resources may be addresses, communication parameters, application parameters, or complex sets of data like binding tables or even the entire executable application program.

The network management basically makes use of the services offered by the application layer. Each device implementing a given configuration mode (see below) has to implement the services and resources specified in the relevant “profile” (set of specifications, see below).
For managing the devices, these services are used within procedures. The different configuration modes make use of an identified set of procedures, which are described in the “configuration management” part. As indicated above, and further demonstrated in the Configuration Modes section below, KNX supports a broad spectrum of solutions here, ranging from centralized and semi- centralised “master-slave” versions, over entirely peer-to-peer to strictly local configuration styles.

However, mechanisms and Resources are not enough. Solid Network Management has to abide by a set of consistency rules, global ones as well as within and among profiles, and general Good Citizenship. For example, some of these rules govern the selection of the (numerical value of) the address when binding Datapoints.

But now, we first turn our attention to how the Communication System’s messaging solutions for applications as well as management, beginning with the physical transmission media.

Communication: Physical Layers

The KNX system offers the choice for the manufacturers, depending on his market requirements and habits, to choose between several physical layers, or to combine them. With the availability of routers, and combined with the powerful Interworking, multi-media, and also multi-vendor configurations can be built.

The different media are :

  • TP 1 (basic medium inherited from EIB) providing a solution for twisted pair cabling, using a SELV network and supply system. Main characteristics are: data and power transmission with one pair (devices with limited power consumption may be fed by the bus), and asynchronous character oriented data transfer and half duplex bi-directional communication. TP 1 transmission rate is 9600 bit/s.
    TP1 implements a CSMA/CA collision avoidance. All topologies may be used and mixed ( line, star, tree, ….)
  • PL 110 (also inherited from EIB) enables communication over the mains supply network. Main characteristics are: spread frequency shift keying signalling, asynchronous transmission of data packets and half duplex bi-directional communication. PL 110 uses the central frequency 110 kHZ and has a data rate of 1200 bit/s.
    PL110 implements CSMA and is compliant to EN 50065-1 (in the frequency band without standard access medium protocol).
  • RF enables communication via radio signals in the 868,3 MHz band for Short Range Devices. Main characteristics are: Frequency Shift Keying, maximum duty cycle of 1%, 32 768 cps, Manchester data encoding.
  • Beyond these Device Network media, KNX has unified service- and integration solutions for IP-enabled (1) media like Ethernet (IEEE 802.2), Bluetooth, WiFi/Wireless LAN (IEEE 802.11), “FireWire” (IEEE 1394) etc., as explained in the KNXnet/IP section below.

Communication: Common Kernel and Message Protocol

The Communication System must tend to the needs of the Application Models, Configuration and Network Management. On top of the Physical Layers and their particular Data Link Layer, a Common Kernel model is shared by all the devices of the KNX Network; in order to answer all requirements, it includes a 7 Layers OSI model compliant communication system.

  • Data Link Layer General, above Data Link Layer per medium, provides the medium access control and the logical link control.
  • Network Layer provides a segment wise acknowledged telegram; it also controls the hop count of a frame. Network Layer is of interest mainly for nodes with routing functionality.
  • Transport Layer (TL) enables 4 types communication relationship between communication points: one-to-many connectionless (multicast), one-to-all connectionless (broadcast), one-to-one connectionless, one-to-one connection-oriented. For freely bound models (see below), TL also separates (“indirects”) the network multicast address from the internal representation.
  • Session and presentation Layers are empty.
  • Application Layer offers a large “toolkit” variety of application services to the application process. These services are different depending on the type of communication used at transport layer. Services related to point-to-point communication and broadcast mainly serve to the network management, whereas services related to multicast are intended for runtime operation.

Remember KNX does not fix the choice of microprocessor. Since in addition, KNX covers an extensive range of configuration and device models, the precise requirements governing a particular implementation are established in detailed Profiles, in line with the Configuration Modes. Within these boundaries, the KNX developer is encouraged to find the optimal solution to accommodate his implementation requirements! This is expounded in later sections.

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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

Easy to install

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

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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Transformer Oil Diagnostics

Transformer Oil Diagnostics

In addition to dissipating heat due to losses in a transformer, insulating oil provides a medium with high dielectric strength in which the coils and core are submerged. This allows the transformers to be more compact, which reduces costs. Insulating oil in good condition will withstand far more voltage across connections inside the transformer tank than will air. An arc would jump across the same spacing of internal energized components at a much lower voltage if the tank had only air. In addition, oil conducts heat away from energized components much better than air.

Over time, oil degrades from normal operations, due to heat and contaminants. Oil cannot retain high dielectric strength when exposed to air or moisture. Dielectric strength declines with absorption of moisture and oxygen. These contaminants also deteriorate the paper insulation. For this reason, efforts are made to prevent insulating oil from contacting air, especially on larger power transformers. Using a tightly sealed transformer tank is impractical, due to pressure variations resulting from thermal expansion and contraction of insulating oil. Common systems of sealing oil-filled transformers are the conservator with a flexible diaphragm or bladder or a positivepressure inert-gas (nitrogen) system. Reclamation GSU transformers are generally purchased with conservators, while smaller station service transformers have a pressurized nitrogen blanket on top of oil. Some station service transformers are dry-type, self-cooled or forcedair cooled.

Conservator System

A conservator is connected by piping to the main transformer tank that is completely filled with oil. The conservator also is filled with oil and contains an expandable bladder or diaphragm between the oil and air to prevent air from contacting the oil. Figure 1 is a schematic representation of a conservator system (figure 1 is an actual photo of a conservator).

Figure 1: Conservator with Bladder

Figure 1: Conservator with Bladder

Air enters and exits the space above the bladder/diaphragm as the oil level in the main tank goes up and down with temperature. Air typically enters and exits through a desiccant-type air dryer that must have the desiccant replaced periodically. The main parts of the system are the expansion tank, bladder or diaphragm, breather, vent valves, liquid-level gauge and alarm switch. Vent valves are used to vent air from the system when filling the unit with oil. A liquid-level gauge indicates the need for adding or removing transformer oil to maintain the proper oil level and permit flexing of the diaphragm.

Oil-Filled, Inert-Gas System

A positive seal of the transformer oil may be provided by an inert-gas system. Here, the tank is slightly pressurized by an inert gas such as nitrogen. The main tank gas space above the oil is provided with a pressure gauge (figure 12. Since the entire system is designed to exclude air, it must operate with a positive pressure in the gas space above the oil; otherwise, air will be admitted in the event of a leak. Smaller station service units do not have nitrogen tanks attached to automatically add gas, and it is common practice to add nitrogen yearly each fall as the tank starts to draw partial vacuum, due to cooler weather. The excess gas is expelled each summer as loads and temperatures increase. Some systems are designed to add nitrogen automatically (figure 2) from pressurized tanks when the pressure drops below a set level. A positive pressure of approximately 0.5 to 5 pounds per square inch (psi) is maintained in the gas space above the oil to prevent ingress of air. This system includes a nitrogen gas cylinder; three-stage, pressure-reducing valve; high-and low-pressure gauges; high-and low-pressure alarm switch; an oil/condensate sump drain valve; an automatic pressure-relief valve; and necessary piping.

Figure 2: Typical Transformer Nitrogen System

Figure 2: Typical Transformer Nitrogen System

The function of the three-stage, automatic pressure-reducing valves is to reduce the pressure of the nitrogen cylinder to supply the space above the oil at a maintained pressure of 0.5 to 5 psi. The high-pressure gauge normally has a range of 0 to 4,000 psi and indicates nitrogen cylinder pressure. The low-pressure gauge normally has a range of about -5 to +10 psi and indicates nitrogen pressure above the transformer oil. In some systems, the gauge is equipped with high- and low-pressure alarm switches to alarm when gas pressure reaches an abnormal value; the high-pressure gauge may be equipped with a pressure switch to sound an alarm when the supply cylinder pressure is running low. A sump and drain valve provide a means for collecting and removing condensate and oil from the gas. A pressure-relief valve opens and closes to release the gas from the transformer and, thus, limit the pressure in the transformer to a safe maximum value.

As temperature of a transformer rises, oil expands, and internal pressure increases, which may have to be relieved. When temperature drops, pressure drops, and nitrogen may have to be added, depending on the extent of the temperature change and pressure limits of the system.


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Procedure for the establishment of a new substation

Procedure for the establishment of a new substation

Large consumers of electricity are invariably supplied at HV. On LV systems operating at 120/208 V (3-phase 4-wires), a load of 50 kVA might be considered to be “large”, while on a 240/415 V 3-phase system a “large” consumer could have a load in excess of 100 kVA. Both systems of LV distribution are common in many parts of the world. As a matter of interest, the IEC recommends a “world” standard of 230/400 V for 3-phase 4-wire systems.

This is a compromise level and will allow existing systems which operate at 220/380 V and at 240/415 V, or close to these values, to comply
with the proposed standard simply by adjusting the off-circuit tapping switches of standard distribution transformers.

The distance over which the load has to be transmitted is a further factor in considering an HV or LV service. Services to small but isolated rural consumers are obvious examples. The decision of a HV or LV supply will depend on local circumstances and considerations such as those mentioned above, and will generally be imposed by the utility for the district concerned.

When a decision to supply power at HV has been made, there are two widely followed methods of proceeding:

  1. The power-supplier constructs a standard substation close to the consumer’s premises, but the HV/LV transformer(s) is (are) located in transformer chamber(s) inside the premises, close to the load centre
  2. The consumer constructs and equips his own substation on his own premises, to which the power supplier makes the HV connection

In method no. 1 the power supplier owns the substation, the cable(s) to the transformer(s), the transformer(s) and the transformer chamber(s), to which he has unrestricted access. The transformer chamber(s) is (are) constructed by the consumer (to plans and regulations provided by the supplier) and include plinths, oil drains, fire walls and ceilings, ventilation, lighting, and earthing systems, all to be approved by the supply

The tariff structure will cover an agreed part of the expenditure required to provide the service. Whichever procedure is followed, the same principles apply in the conception and realization of the project. The following notes refer to procedure no. 2.

Preliminary information

Before any negotiations or discussions can be initiated with the supply authorities, the following basic elements must be established:

Maximum anticipated power (kVA) demand

Determination of this parameter is described in Chapter B, and must take into account the possibility of future additional load requirements. Factors to evaluate at this stage are:

  • The utilization factor (ku)
  • The simultaneity factor (ks)

Layout plans and elevations showing location of proposed substation

Plans should indicate clearly the means of access to the proposed substation, with dimensions of possible restrictions, e.g. entrances corridors and ceiling height, together with possible load (weight) bearing limits, and so on, keeping in mind that:

  • The power-supply personnel must have free and unrestricted access to the HV equipment in the substation at all times
  • Only qualified and authorized consumer’s personnel are allowed access to the substation
  • Some supply authorities or regulations require that the part of the installation operated by the authority is located in a separated room from the part operated by the customer.

Degree of supply continuity required

The consumer must estimate the consequences of a supply failure in terms of its duration:

  • Loss of production
  • Safety of personnel and equipment

The utility must give specific information to the prospective consumer.

Project studies

From the information provided by the consumer, the power-supplier must indicate:

The type of power supply proposed and define

  • The kind of power-supply system: overheadline or underground-cable network
  • Service connection details: single-line service, ring-main installation, or parallel
    feeders, etc.
  • Power (kVA) limit and fault current level

The nominal voltage and rated voltage

(Highest voltage for equipment) Existing or future, depending on the development of
the system.

Metering details which define:

  • The cost of connection to the power network
  • Tariff details (consumption and standing charges)


Before any installation work is started, the official agreement of the power-supplier must be obtained. The request for approval must include the following information, largely based on the preliminary exchanges noted above:

  • Location of the proposed substation
  • One-line diagram of power circuits and connections, together with earthing-circuit
  • Full details of electrical equipment to be installed, including performance
  • Layout of equipment and provision for metering components
  • Arrangements for power-factor improvement if eventually required
  • Arrangements provided for emergency standby power plant (HV or LV) if eventually

The utility must give official approval of the equipment to be installed in the substation, and of proposed methods of installation.


When required by the authority, commissioning tests must be successfully completed before authority is given to energize the installation from the power supply system.

After testing and checking of the installation by an independent test authority, a certificate is granted which permits the substation to be put into service.

Even if no test is required by the authority it is better to do the following verification tests:

  • Measurement of earth-electrode resistances
  • Continuity of all equipotential earth-and safety bonding conductors
  • Inspection and testing of all HV components
  • Insulation checks of HV equipment
  • Dielectric strength test of transformer oil (and switchgear oil if appropriate)
  • Inspection and testing of the LV installation in the substation,
  • Checks on all interlocks (mechanical key and electrical) and on all automatic
  • Checks on correct protective-relay operation and settings
    It is also imperative to check that all equipment is provided, such that any properly executed operation can be carried out in complete safety. On receipt of the certificate of conformity (if required):
  • Personnel of the power-supply authority will energize the HV equipment and check
    for correct operation of the metering
  • The installation contractor is responsible for testing and connection of the LV installation
    When finally the substation is operational:
  • The substation and all equipment belongs to the consumer
  • The power-supply authority has operational control over all HV switchgear in the substation, e.g. the two incoming load-break switches and the transformer HV switch (or CB) in the case of a MV switchgear, together with all associated HV earthing switches
  • The power-supply personnel has unrestricted access to the HV equipment
  • The consumer has independent control of the HV switch (or CB) of the transformer(s) only, the consumer is responsible for the maintenance of all substation equipment, and must request the power-supply authority to isolate and earth the switchgear to allow maintenance work to proceed.
    The power supplier must issue a signed permitto- work to the consumers maintenance personnel, together with keys of locked-off isolators, etc. at which the isolation has been carried out.


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Galaxy 7000 UPS 250-500kVA by APC

Galaxy 7000 UPS 250-500kVA by APC

Three-phase Galaxy 7000, 250 to 500 kVA (up to 4 MVA in parallel configurations), includes cutting-edge technologies for high-power applications.

Calling on over 40 years of experience in the Critical Power and Cooling Services division of Schneider Electric, the leader in complete, high-quality electrical power solutions, Galaxy 7000 offers optimised performance for data centers, infrastructure and industrial processes. The compact size, back-to-back or back-to-wall installation enables more room to be utilised for other equipments in the technical room than traditional UPS systems. The UPS can be upgraded to ensure available and secure power infrastructure for current as well as future demands.


Galaxy 7000 increases the productivity of these applications by providing continuity of service through secure supply solutions that are flexible, adaptable and upgradeable. Galaxy 7000 provides high-quality energy, compatible with all loads, with a very high level of availability. The variety of architectures meets the specific needs of each installation and allows easy upgrading. The communication capabilities and proactive services provided by Schneider Electric, the most complete and available worldwide, make for highly effective maintenance.

  • Data Centers
    The strategic and economic importance of data centers made it necessary to set up the ANSI/TIA site typology (TIER I to IV). It presents the necessary functions of the major components, including supply via UPSs, to ensure consistency and obtain a high level of overall availability.
    Galaxy 7000, through its design and many possibilities for parallel connection, as well as its compatibility with STS (static transfer switch) systems, meets TIER IV requirements for fault-tolerant sites offering the highest level of availability (99.995%).
    Combined with STS units, Galaxy 7000 can supply energy via two or three different channels for dual or triple-attach applications and also offers supervision, network administration and remote-control solutions. Galaxy 7000 is ideal for the large (over 500 square metre) data centers of banks, insurance companies, internet and colocation services, telecoms, etc. where 24/365 operation is mandatory and preventive maintenance and upgrades must not require system shutdown.
  • Fig. 2. Applications such as data centers, infrastructure and industrial processes.

    Fig. 2. Applications such as data centers, infrastructure and industrial processes.

  • Infrastructure and buildings
    Service continuity is also required for infrastructure (airports, ports, tunnels) as well as the operation and technical monitoring (via SCADA and BMS systems) of shopping centres, hospitals, office buildings, etc. Galaxy 7000 is perfectly suited to the needs of these communicating, frequently upgraded applications thanks to its power ratings, extension possibilities and communication capabilities.
  • Industrial processes
    Operation in industrial environments requires equipment capable of maintaining processes, without failure, under difficult conditions, including dust, humidity, vibrations, major variations in temperature, etc. Due to its high electrical and mechanical level of performance, Galaxy 7000 meets these specific needs.
    Technical files are available for all the applications specified by design offices, including Ni-Cad batteries for the chemical and petrochemical industries, high IP values, heavy-duty reinforced cabinets, dust filters, marine configurations, rated voltages up to 440 V, etc. The MGE UPS SYSTEMS design office, in conjunction with a specialised industrial organisation, can also handle uncommon conditions, e.g. outdoor installations, anti-vibration bases for marine applications, special paints with the corresponding labels, etc.
  • Colour
    Light grey RAL 9023

Strong Points

Galaxy 7000 design combines the best technology (double conversion) with the most recent innovations to supply high-quality power, available 24/365, to high-power applications, whatever the situation in the distribution system.

  • Double conversion technology (VFI as per IEC 62040-3/EN 62040-3).
    This is the only technology that insulates the load from the upstream network and completely regenerates the output voltage, thus providing high-quality, stable power.
  • IGBT-based, PFC sinusoidal-current input rectifier. The rectifier draws sinusoidal current, without any reactive power, thus avoiding disturbances upstream by reducing harmonic reinjection.
    • Very low current total harmonic distortion THDI, less than 5%.
    • Input power factor (PF) greater than 0.99 from 50% load upwards.
    These performance levels, combined with the three-phase input not requiring neutral, offer substantial savings in terms of cables and equipment.

    Fig. 3. Three-phase, PFC sinusoidal-current rectifier, with DualPack IGBTs.

    Fig. 3. Three-phase, PFC sinusoidal-current rectifier, with DualPack IGBTs.

  • Battery charger separated from the AC input. The chopper is supplied via the rectifier output and is thus protected against fluctuations on the AC input. Battery recharge is adjusted as a function of the temperature.
  • A check on the phase sequence is run to protect the power system from the effects of incorrect connections.
  • Wide input-voltage (250 to 470 V) and frequency (45 to 65 Hz) range. This is made possible by double-conversion technology and the PFC rectifier which is compatible with all sources and with disturbed distribution systems (voltages as low as 250 V for 30% load).

    Fig. 4. Wide input-voltage range.

    Fig. 4. Wide input-voltage range.

  • Soft start. This system provides total compatibility with gensets through gradual start of the rectifier, in addition to a PF of 0.99. It makes it possible:
    • when AC power is absent, to progressively transfer the load from the battery to the genset
    • when the normal AC source returns to tolerances, to delay transfer from the battery to the rectifier, thus avoiding excessive variations on the AC source.
    • in a parallel system, to set up sequential start-up of the inverters.

    Fig. 5. Soft start walk-in ramp with time delay.

    Fig. 5. Soft start walk-in ramp with time delay.

  • Cold start on battery power if the AC source is absent or disturbed, even in parallel systems.
  • High-quality output voltage (380, 400, 415 or440 V) for all types of loads with:
    • THDU < 3%
    • output PF = 09 for all types of load.
    The range is suitable for the most recent non-linear and computer loads, called capacitive loads, with a leading PF close to 0.9 and a high crest factor.
  • Output voltage adjustable to ± 3% of the rated value (in 0.5 V steps) to take into account voltage drops in long cables.
  • Excellent response to load step changes, < 2% for 100 to 0% or 0 to 100% and return to the ± 1% tolerances within 100 ms.
  • High current-limiting capacity for inverter short-circuits (2.5 In, 150 ms) to facilitate discrimination with downstream protective devices and accept high crest factors, 2.4:1 up to 3:1, depending on the voltage and power levels.
  • Intelligent thermal-overload capacity curve for better performance. The curve is adjusted as a function of the ambient temperature, 1.5 In / 30 seconds, 1.25 In / 10 minutes.

Advanced management to extend battery life

Galaxy 7000 proposes backup times from 5 minutes to 2 hours with a rapid charger (recharge < 6 hours for 10-minute backup time). Backup time remains available due to digital battery management and the protection systems.

  • The standard “DigiBat™” system monitors the battery to forward information and maximise performance. Based on a large number of parameters (percent load, temperature, battery type and age), DigiBat controls the battery charge voltage and continuously calculates:
    • the real available backup time
    • the remaining battery life (1).
    DigiBat also offers:
    • automatic entry of battery parameters
    • test on battery status to preventively detect operating faults
    • automatic battery discharge test at adjustable time intervals
    • protection against deep discharge taking into account the discharge rate, with a circuit breaker to isolate the battery. The breaker opens automatically after double the specified backup time plus two hours (sleep mode to provide vital functions)
    • limiting of the battery charge current (0.05 C10 to 0.1 C10)
    • gradual alarm signalling the end of backup time
    • numerous automatic tests.Fig. 10. Digibat.
  • The B1000 battery monitoring or “Cellwatch” option monitors all battery strings 24/365 and displays a failure prediction for each block.

User-friendly interface for more dependable operation

Galaxy 7000 has a control and display interface offering intuitive functions. Based on graphs and pictograms, the interface can be set up in 19 languages including Chinese, Korean, Thai, Indonesian, Turkish and Greek. It includes a graphical display for time-stamped events and useful operating statistics. For operating personnel, that is an essential aspect in facilitating decisions. Simple and user-friendly, the interface enhances safety and comfort.

  • Graphical display with HD, B&W touch screen (SVGA).
  • Animated mimic panel.
  • Menu keys and direct access to display functions.
  • Buzzer.
  • Remote supervision that can run under many BMS systems and network
    supervisors via the communication cards.
  • Time-stamping of last 2500 events.
  • On-line help to assist with the displayed messages.
  • Multi-mode for parallel units (modular UPSs in parallel, parallel UPSs with SSC, frequency converters in parallel), i.e. it is possible to read the measurements of any unit on any unit, or to read system data.Fig. 11. HMI with display, LEDs, keys and mimic panel

Advanced communication

Galaxy 7000 offers the entire MGE UPS SYSTEMS range of communication systems designed to meet three essential needs.

  • Inform on UPS operation and its environment, warn users, wherever they may be, concerning any potential and existing problems.
  • Protect server data by automatic, clean shutdown of operating systems
  • Actively supervise an entire set of UPSs.
    These functions are carried out by hot-swappable communication cards running
    under different protocols, depending on the environment in which Galaxy 7000 is
  • Standard relay card with programmable dry contacts (4 logic inputs and 6 logic
  • INMC (Industrial Network Management Card) communication card with two
    • JBus/ModBus RS485/RS232 protocol for communication with a BMS
    • Ethernet 10/100 Mbps protocol using the Https standard (secure connection) for
    supervision via the web.
    Each UPS then has its own IP address making it possible for the user to:
    • supervise and control the UPS via a simple browser (HTTP)
    • interface with an SNMP administration system (HP Openview, etc.)
    • communicate with shutdown modules installed on the protected servers
    • set up external temperature and humidity monitoring (sensor environment)
    • receive e-mail alarms.
  • NMTC (Network Management Teleservice Card) communication card with three
    • JBus/ModBus RS232/RS485
    • Ethernet 10/100 Mbps using the Https protocol.
    The functions are identical to the INMC card, with in addition:
    • a modem connection may be used to connect the UPS to the MGE Teleservice
    centre for remote monitoring.
  • Life Cycle Monitoring software for optimised maintenance.
  • Compatible with CPSOL software from Schneider Electric for complete
    installation design.


Galaxy 7000 uses the latest technical and mechanical advances in terms of electrical components and power electronics. The greatly reduced number of components offers:

  • an overall solution that is very compact, but high accessible for maintenance
  • integration of many functions in a single cabinet. The batteries, installed in a
    separate cabinet, can be hot-swapped (with the UPS supplying the load).

The UPS can be installed in both technical and computer rooms.

  • The UPS can operate correctly back to the wall or back to back, but it is preferable to leave some space (> 600 mm) for easier maintenance.
  • Leave one meter of free space in front of the UPS for door opening.
  • At least 500 mm of clearance above the UPS is required.

Equipment and diagrams

Galaxy 7000 UPS units offer the following equipment and functions.

Standard configuration

  • IGBT-based, PFC three-phase rectifier
  • Phase-sequence check on input
  • Chopper for battery charging, insulated from AC input, charge adjusted for ambient temperature
  • Static switch (except parallel UPS units)
  • Manual bypass (except parallel UPS units)
  • Three-phase IGBT inverter with freefrequency PWM chopping
  • Redundant ventilation for power components
  • HMI with graphical interface, 19 languages, menu, function and ON/OFF keys
  • Mimic panel with status LEDs
  • Time-stamping of last 2500 events
  • Battery protected against deep discharges by a circuit breaker
  • Cold start on battery power
  • Soft start with walk-in ramp and sequential start in parallel configurations
  • EMC, level B
  • Parallel connection of modular or parallel UPS units
  • DigiBat digital battery monitoring and calculation of true backup time
  • Programmable relay card, dry contacts, 4 logic inputs, 6 logic outputs


  • Connection through the top
  • Isolation/voltage matching transformer
  • Synchronisation module
  • B1000 or Cellwatch battery-monitoring system for block by block management
  • Lightning arrestor (built into the UPS cabinet)
  • Backfeed protection
  • Synchronisation module
  • Multi-standard communication cards:
    - Jbus/Modbus + Ethernet 10/100
    - Jbus/Modbus + Ethernet 10/100 + Modem
    - 2 ports with dry contacts and/or remote shutdown
  • Battery circuit breaker unit
  • Supervision and shutdown software:
  • Enterprise Power Manager V.2

Electrical characteristics

Electrical characteristics


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Testing performances of IEC 61850 GOOSE messages

Testing performances of IEC 61850 GOOSE messages

One of the frequent requests for relay protection devices is support for the IEC 61850 standard. As part of the standard special messages are also planned for a quick exchange of information between the IEDs – so called  GOOSE (Generic Object-Oriented SubStation Event). These are mainly trip, interlocking, breaker failure and similar signals. Time of transfer of these signals is critical, its delay may cause undesirable blackouts  or damage to equipment.

In this paper we explore which software architecture is most appropriate to achieve the required performance. Software for sending / receiving GOOSE messages can be located in real time (RT) or user space of the operating system. We will consider the RT and user space implementations of two different microprocessor architecture – ARM9 and PowerPC.
Performance degradation can occur from 2 reasons:

  • Protection  function has the highest priority. At least 500 μs during each millisecond GOOSE thread will be deprived of CPU time.
  • In the case of pure user-space implementation, the operating system will interrupt GOOSE task in a completely nondeterministic way.

User Space Test

To test the performance of GOOSE messages in user space, the environment is developed based on the ARM7 architecture:

  • ARM7 with integrated Ethernet for sending, receiving and time-stamping of messages.
  • The PC application for setting parameters and collecting the results.
Figure 1 Test configuration for user space test
Figure 1 Test configuration for user space test

The essence of the test is as follows: ARM7 board launches a series of messages and records the time for each outgoing message. ARM9 and PowerPC boards are set up to immediately respond to received GOOSE messages  with identical message and  with the same serial number.
ARM7 registers  the answer and uses the serial number to match with the original message and calculates the elapsed time.

Figure 2 Analysis time
Figure 2 Analysis time

On the figure above we can see the analysis of time. A and B are negligible. Due to the nature of the test 2C + D  can be accurately measured but we can’t know exactly  the amounts of C and D are respectively. But ultimately this is not important from the point of standards. Let’s look at test results. ARM7 board launches a series of GOOSE messages with pause of 100ms. Results are measured and displayed in Excel.

To make it more realistic result overcurrent protection was turned on.  Y axis shows the time in milliseconds and the X axis shows GOOSE messages.

Figure 3 ARM9 100ms (X axis - number of messages, the Y axis the time of transfer)
Figure 3 ARM9 100ms (X axis – number of messages, the Y axis the time of transfer)

We see that during 20 seconds response time oscillates around 2 milliseconds. The next step was to involve several protection functions. It is expected that the GOOSE performance will drop.

This is actually happening as we see in the following figure:

Figure 4 ARM9 100ms, 700μs (X axis - number of messages, the Y axis the time of transfer)
Figure 4 ARM9 100ms, 700μs (X axis – number of messages, the Y axis the time of transfer)

The time now oscillates about 7 ms. Although it is expected that the performance will decline, it is still above expectations. 7 milliseconds is still enough for some applications. These are the results from the ARM9 platform. PowerPC platform has proved to be something better, because it has almost 2 times more processing power. On the next 2 images we see the results.

Figure 5 PowerPC 100ms (X axis - number of messages, the Y axis the time of transfer)
Figure 5 PowerPC 100ms (X axis – number of messages, the Y axis the time of transfer)

Slika 6. PowerPC 100ms, 700μs (X osa – redni broj poruke, Y osa vreme transfera)
Figure 6 PowerPC 100ms, 700μs (X axis – number of messages, the Y axis the time of transfer)

In a small load time oscillates around 0.8 ms and at most about 2.5 ms. The measured  times are suitable for  a solid range of applications. Unfortunately, these times are only valid if the GOOSE task is only active task. In the case of other tasks – for example, disturbance recorder, event recorder, embedded web server, IEC 61850 MMS server and so on … transfer time become unpredictable and can go up to 80ms, which is of course unacceptable.

Real Time Test

Figure 7 Test configuration for real-time test
Figure 7 Test configuration for real-time test

Although the real time GOOSE is something more difficult to implement, it offers some significant advantages as we shall see. Test environment for real-time is significantly different. The network analyzer was used. The program is available as a free download from the Internet (1). The essence of the test is as follows: protection relays is configured to receive GOOSE messages from a laptop computer and to immediately respond with the same value in the dataset. When analyzing a series of messages network analyzer will come to the moment when the relay and laptops are sending an identical value.
The time between the moment when the laptop starts broadcasting and the moment the relay begins to broadcast the same value as the laptop is the required time.

In the following figure we can see the results displayed in the network analyzer.

Figure 8 Ethereal Network Analyzer
Figure 8 Ethereal Network Analyzer

Figure 9 Goose series with a time of receipt of messages, network addresses and protocol label
Figure 9 Goose series with a time of receipt of messages, network addresses and protocol label

Message number 42 is from a laptop, a message 43 from relay protection. If you subtract the time of receipt: 3.757 to 3.753 = 4msec. When measurements  are repeated result oscillates around 4ms. The reason for this is that the task for sending and receiving is set to be run every 2 milliseconds.


At first glance, real-time and user space implementation operates in a similar timeframe. But there is a substantial difference. GOOSE  RT implementation task may share the processor with an arbitrary number of other task such as the disturbance recorder and others. This architecture greatly reduces the ultimate cost of the device and gives the user more functionality. Otherwise the GOOSE software would have to reside on separate hardware.



Veljko Milisavljević | ABS Control Systems, Serbia

Veljko Milisavljević

Veljko Milisavljević


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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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Maintenance Of SF6 Gas Circuit Breakers

Maintenance Of SF6 Gas Circuit Breakers

Sulfur Hexafluoride (SF6) is an excellent gaseous dielectric for high voltage power applications. It has been used extensively in high voltage circuit breakers and other switchgears employed by the power industry.

Applications for SF6 include gas insulated transmission lines and’gas insulated power distributions. The combined electrical, physical, chemical and thermal properties offer many advantages when used in power switchgears.

Some of the outstanding properties of SF6 making it desirable to use in power applications are:

  • High dielectric strength
  • Unique arc-quenching ability
  • Excellent thermal stability
  • Good thermal conductivity

Properties Of SF6 (Sulfur Hexafuoride) Gas

  • Toxicity – SF6 is odorless, colorless, tasteless, and nontoxic in its pure state. It can, however, exclude oxy­gen and cause suffocation. If the normal oxygen content of air is re­duced from 21 percent to less than 13 percent, suffocation can occur without warning. Therefore, circuit breaker tanks should be purged out after opening.
  • Toxicity of arc products – Toxic decomposition products are formed when SF6 gas is subjected to an elec­tric arc. The decomposition products are metal fluorides and form a white or tan powder. Toxic gases are also formed which have the characteristic odor of rotten eggs. Do not breathe the vapors remaining in a circuit breaker where arcing or corona dis­charges have occurred in the gas. Evacuate the faulted SF6 gas from the circuit breaker and flush with fresh air before working on the circuit breaker.
  • Physical properties – SF6 is one of the heaviest known gases with a den­sity about five times the density of air under similar conditions. SF6 shows little change in vapor pressure over a wide temperature range and is a soft gas in that it is more compressible dynamically than air. The heat trans­fer coefficient of SF6 is greater than air and its cooling characteristics by convection are about 1.6 times air.
  • Dielectric strength – SF6 has a di­electric strength about three times that of air at one atmosphere pressure for a given electrode spacing. The dielectric strength increases with increasing pressure; and at three atmospheres, the dielectric strength is roughly equivalent to transformer oil. The heaters for SF6 in circuit breakers are required to keep the gas from liquefying because, as the gas liquifies, the pressure drops, lowering the dielectric strength. The exact dielectric strength, as compared to air, varies with electrical configuration, electrode spacing, and electrode configuration.
  • Arc quenching – SF6 is approxi­mately 100 times more effective than air in quenching spurious arcing. SF6 also has a high thermal heat capacity that can absorb the energy of the arc without much of a temperature rise.
  • Electrical arc breakdown – Because of the arc-quenching ability of SF6, corona and arcing in SF6 does not occur until way past the voltage level of onset of corona and arcing in air. SF6 will slowly decompose when ex­posed to continuous corona.

All SF6 breakdown or arc products are toxic. Normal circuit breaker operation produces small quantities of arc products during current interruption which normally recombine to SF6. Arc products which do not recombine, or which combine with any oxygen or moisture present, are normally re­moved by the molecular sieve filter material within the circuit breaker.

Handling Nonfaulted SF6

The procedures for handling nonfaulted SF6 are well covered in manufacturer’s instruction books. These procedures normally consist of removing the SF6 from the circuit breaker, filtering and storing it in a gas cart as a liquid, and transferring it back to the circuit breaker after the circuit breaker maintenance has been performed. No special dress or precautions are required when handling nonfaulted SF6.

Handling Faulted SF6


  • Faulted SF6 gas – Faulted SF6 gas smells like rotten eggs and can cause nausea and minor irritation of the eyes and upper respiratory tract. Normally, faulted SF6 gas is so foul smelling no one can stand exposure long enough at a concentration high enough to cause permanent damage.
  • Solid arc products - Solid arc products are toxic and are a white or off-white, ashlike powder. Contact with the skin may cause an irritation or possible painful fluoride burn. If solid arc products come in contact with the skin, wash immediately with a large amount of water. If water is not available, vacuum off arc products with a vacuum cleaner.

Clothing and safety equipment requirements

When handling and re­ moving solid arc products from faulted SF6, the following clothing and safety equipment should be worn:

  • Coveralls – Coveralls must be worn when removing solid arc products. Coveralls are not required after all solid arc products are cleaned up. Disposable coveralls are recommended for use when removing solid arc products; however, regular coveralls can be worn if disposable ones are not available, provided they are washed at the end of each day.
  • Hoods – Hoods must be worn when removing solid arc products from inside a faulted dead-tank circuit breaker.
  • Gloves – Gloves must be worn when solid arc products are hah-died. Inexpensive, disposable gloves are recommended. Non-disposable gloves must be washed in water and allowed to drip-dry after use.
  • Boots – Slip-on boots, non-disposable or plastic disposable, must be worn by employees who enter eternally faulted dead-tank circuit breakers. Slip-on boots are not required after the removal of solid arc products and vacuuming. Nondisposable boots must be washed in water and dried after use.
  • Safety glasses – Safety glasses are recommended when handling solid arc products if a full face respirator is not worn.
  • Respirator – A cartridge, dust-type respirator is required when entering an internally faulted dead-tank circuit breaker. The respirator will remove solid arc products from air breathed, but it does not supply oxygen so it must only be used when there is sufficient oxygen to support life. The filter and cartridge should be changed when an odor is sensed through the respirator. The use of respirators is optional for work on circuit breakers whose in­ terrupter units are not large enough for a man to enter and the units are well ventilated.
    Air-line-type respirators should be used when the cartridge type is ineffective due to providing too short a work time before the cartridge becomes contaminated and an odor is sensed.
    When an air-line respirator is used, a minimum of two working respirators must be available on the job before any employee is allowed to enter the circuit breaker tank.

Disposal of waste

All materials used in the cleanup operation for large quantities of SF6 arc products shall be placed in a 55­ gal drum and disposed of as hazardous waste.

The following items should be disposed of:

  • All solid arc products
  • All disposable protective clothing
  • All cleaning rags
  • Filters from respirators
  • Molecular sieve from breaker and gas cart
  • Vacuum filter element


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Wind power storage development is essential for renewable energy technologies to become economically feasible. There are many different ways in which one can store electrical energy, the following outlines the various media used to store grid-ready energy produced by wind turbines. For more on applications of these wind storage technologies, read Solving the use-it-or-lose-it wind energy problem

Electrochemical Batteries

Familiar electrochemical batteries include nickel-cadmium (NiCad), lithium-ion (Li-ion, and others. Electrochemical batteries consist of two or more electrochemical cells. The cells use chemical reaction(s) to create a flow of electrons – electric current. Primary elements of a cell include the container, two electrodes (anode and cathode), and electrolyte material. The electrolyte is in contact with the electrodes. Current is created by the oxidation-reduction process involving chemical reactions between the cell’s electrolyte and electrodes.

Familiar electrochemical batteries include nickel-cadmium (NiCad), lithium-ion (Li-ion, and others

Familiar electrochemical batteries include nickel-cadmium (NiCad), lithium-ion (Li-ion, and others

When a battery discharges through a connected load, electrically charged ions in the electrolyte that are near one of the cell’s electrodes supply electrons (oxidation) while ions near the cell’s other electrode accept electrons (reduction), to complete the process. The process is reversed to charge the battery, which involves ionizing of the electrolyte. An increasing number of chemistries are used for this process.

Flow Batteries

Some electrochemical batteries (e.g., automobile batteries) contain electrolyte in the same container as the cells (where the electrochemical reactions occur). Other battery types – called flow batteries – use electrolyte that is stored in a separate container (e.g., a tank) outside of the battery cell container. Flow battery cells are said to be configured as a ‘stack’. When flow batteries are charging or discharging, the electrolyte is transported (i.e., pumped) between the electrolyte container and the cell stack. Vanadium redox and Zn/Br are two of the more familiar types of flow batteries. A key advantage to flow batteries is that the storage system’s discharge duration can be increased by adding more electrolyte (and, if needed to hold the added electrolyte, additional electrolyte containers). It is also relatively easy to replace a flow battery’s electrolyte when it degrades.


Capacitors store electric energy as an electrostatic charge. An increasing array of larger capacity capacitors have characteristics that make them well-suited for use as energy storage. They store significantly more electric energy than conventional capacitors. They are especially well-suited to being discharged quite rapidly, to deliver a significant amount of energy over a short period of time (i.e., they are attractive for high-power applications that require short or very short discharge durations).

Compressed Air Energy Storage

Compressed Air Energy Storage

Compressed Air Energy Storage

Compressed air energy storage (CAES) involves compressing air using inexpensive energy so that the compressed air may be used to generate electricity when the energy is worth more.

To convert the stored energy into electric energy, the compressed air is released into a combustion turbine generator system. Typically, as the air is released, it is heated and then sent through the system’s turbine. As the turbine spins, it turns the generator to generate electricity. For larger CAES plants, compressed air is stored in underground geologic formations, such as salt formations, aquifers, and depleted natural gas fields. For smaller CAES plants, compressed air is stored in tanks or large on-site pipes such as those designed for high-pressure natural gas transmission (in most cases, tanks or pipes are above ground).

Flywheel Energy Storage

Flywheel electric energy storage systems (flywheel storage or flywheels) include a cylinder with a shaft that can spin rapidly within a robust enclosure. A magnet levitates the cylinder, thus limiting friction-related losses and wear. The shaft is connected to a motor/generator. Electric energy is converted by the motor/generator to kinetic energy. That kinetic energy is stored by
increasing the flywheel’s rotational speed. The stored (kinetic) energy is converted back to electric energy via the motor/generator, slowing the flywheel’s rotational speed.

Pumped Hydroelectric

Key elements of a pumped hydroelectric (pumped hydro) system include turbine/generator equipment, a waterway, an upper reservoir, and a lower reservoir. The turbine/generator is
similar to equipment used for normal hydroelectric power plants that do not incorporate storage. Pumped hydro systems store energy by operating the turbine/generator in reserve to pump water uphill or into an elevated vessel when inexpensive energy is available. The water is later released when energy is more valuable. When the water is released, it goes through the turbine which turns the generator to produce electric power.

Superconducting Magnetic Energy Storage

The storage medium in a superconducting magnetic energy storage (SMES) system consists of a coil made of superconducting material. Additional SMES system components include power
conditioning equipment and a cryogenically cooled refrigeration system. The coil is cooled to a temperature below the temperature needed for superconductivity (the material’s ‘critical’ temperature). Energy is stored in the magnetic field created by the flow of direct current in the coil. Once energy is stored, the current will not degrade, so energy can be stored indefinitely (as long as the refrigeration is operational).

Thermal Energy Storage

There are various ways to store thermal energy. One somewhat common way that thermal energy storage is used involves making ice when energy prices are low so the cold that is stored can be used to reduce cooling needs – especially compressor-based cooling – when energy is expensive.

SOURCE: Overview of wind power storage media


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