what is static VAR compensator ?

Question

related with harmonics

Answer 1

Static VAr compensator

From Wikipedia, the free encyclopedia


A static VAr compensator (or SVC) is an electrical device for providing fast-acting reactive power compensation on high-voltage electricity transmission networks. In other words, the SVC provides a system automated impedance matching device. If the power system's Reactive load is too 'Capacitive', the SVC will use reactors to reactively balance the impedance. A similiar procedure is done with a too 'inductive' load, thus providing a power factor closer to unity.

-Principle-

Typically an SVC comprises a bank of individually switched capacitors in conjunction with a thyristor-controlled air- or iron-cored reactor. By means of phase angle modulation switched by the thyristors, the reactor may be variably switched into the circuit, and so provide a continuously variable MVAr injection (or absorption) to the electrical network.

Coarse voltage control is provided by the capacitors; the thyristor-controlled reactor is to provide smooth control. Chopping the reactor into the circuit in this manner injects undesirable odd-order harmonics, and so banks of high-power filters are usually provided to smooth the waveform. Since the filters themselves are capacitive, they also contribute to the net MVAr injection.

Other arrangements such as a thyristor-switched reactor and thyristor-switched capacitors are also practical.

Voltage regulation is provided by means of a closed-loop controller. Remote supervisory control and manual adjustment of the voltage set-point are also common.

-Advantages-

The main advantage of SVCs over simple mechanically-switched compensation schemes is their near-instantaneous response to changes in the system voltage. For this reason they are often operated at close to their zero-point in order to maximise the MVAr reserves they can rapidly provide when required.

They are in general cheaper and require lower maintenance than dynamic compensation schemes such as synchronous compensators.

Answer 2

Description

This project focuses on minimizing the voltage total harmonic distortion when controlling a multilevel converter to act as a static var compensator. Use of resultant theory has enabled the complete set of solutions to be found for switching a multilevel inverter's power electronic devices at the fundamental frequency while eliminating the lower order harmonics. A scheme is also developed to regulate the voltage levels of the multilevel inverter so that it operates in an optimum amplitude modulation index regime.
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Static VAR compensator (SVC) protection practices are presented. Protection schemes comprise a combination of conventional protective relays as well as protection functions performed by the control system. This paper describes different protection functions applicable to SVCs and includes a tabulated overview of possible SVC protection methods. A section is dedicated to testing SVC protection systems. The outlined test procedures may be adopted when commissioning new installations in order to demonstrate proper protection operation. Finally, an important aspect of SVC protective schemes is related to the interactions with transient overvoltages, harmonics, short-circuits, and geomagnetic induced current (GICs) of the transmission network. This paper discusses these issues and identifies areas where careful protection considerations are required.
Revue / Journal Title
IEEE transactions on power delivery (IEEE trans. power deliv.) ISSN 0885-8977 CODEN ITPDE5
Source / Source
Congrès
IEEE/PES summer meeting, San Francisco CA , ETATS-UNIS (24/07/1994)
1995, vol. 10, no3, pp. 1224-1233 (11 ref.)
Langue / Language
Anglais

Editeur / Publisher
Institute of Electrical and Electronics Engineers, New York, NY, ETATS-UNIS (1986) (Revue)

Mots-clés français / French Keywords
Compensation énergie réactive ; Compensateur statique ; Protection ; Méthode essai ; Mise en service ; Essai fonctionnement ; Interaction ; Perturbation ; Article synthèse ;

001d05i01b ;
Localisation / Location
INIST-CNRS, Cote INIST : 21015 B, 35400005374971.0110
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A static VAr compensator (or SVC) is an electrical device for providing fast-acting reactive power compensation on high-voltage electricity transmission networks. In other words, the SVC provides a system automated impedance matching device. If the power system's Reactive load is too 'Capacitive', the SVC will use reactors to reactively balance the impedance. A similiar procedure is done with a too 'inductive' load, thus providing a power factor closer to unity.

Principle

Typically an SVC comprises a bank of individually switched capacitors in conjunction with a thyristor-controlled air- or iron-cored reactor. By means of phase angle modulation switched by the thyristors, the reactor may be variably switched into the circuit, and so provide a continuously variable MVAr injection (or absorption) to the electrical network.

Coarse voltage control is provided by the capacitors; the thyristor-controlled reactor is to provide smooth control. Chopping the reactor into the circuit in this manner injects undesirable odd-order harmonics, and so banks of high-power filters are usually provided to smooth the waveform. Since the filters themselves are capacitive, they also contribute to the net MVAr injection.

Other arrangements such as a thyristor-switched reactor and thyristor-switched capacitors are also practical.

Voltage regulation is provided by means of a closed-loop controller. Remote supervisory control and manual adjustment of the voltage set-point are also common.
Advantages
The main advantage of SVCs over simple mechanically-switched compensation schemes is their near-instantaneous response to changes in the system voltage. For this reason they are often operated at close to their zero-point in order to maximise the MVAr reserves they can rapidly provide when required.

They are in general cheaper and require lower maintenance than dynamic compensation schemes such as synchronous compensators.