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Home / Technical Articles / What is the Static Var Compensator (SVC)?
The Siemens Static Var Compensator in the Radsted high-voltage switchgear station
The Siemens Static Var Compensator in the Radsted high-voltage switchgear station

Static Var Compensator is “a shunt-connected static Var generator or absorber whose output is adjusted to exchange capacitive or inductive current so as to maintain or control specific parameters of the electrical power system (typically bus voltage)”. SVC is based on thyristors without gate turn-off capability. The operating principal and characteristics of thyristors realize SVC variable reactive impedance. SVC includes two main components and their combination:  Thyristor-controlled and Thyristor-switched Reactor (TCR and TSR); and Thyristor-switched capacitor (TSC).

In Figure 1 shows the diagram of SVC:

Figure 1 - Static VAR Compensators (SVC): TCR/TSR, TSC, FC and Mechanically Switched Resistor
Figure 1 - Static VAR Compensators (SVC): TCR/TSR, TSC, FC and Mechanically Switched Resistor

TCR and TSR are both composed of a shunt-connected reactor controlled by two parallel, reverse-connected thyristors. TCR is controlled with proper firing angle input to operate in a continuous manner, while TSR is controlled without firing angle control which results in a step change in reactance.

TSC shares similar composition and same operational mode as TSR, but the reactor is replaced by a capacitor. The reactance can only be either fully connected or fully disconnected zero due to the characteristic of capacitor.

With different combinations of TCR/TSR, TSC and fixed capacitors, a SVC can meet various requirements to absorb/supply reactive power from/to the transmission line.

SOURCE: Reactive Power Compensation of Transmission Lines by Yongan Deng, MASc student at Concordia University

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Hemanth Kumar
    May 04, 2018

    Please explain why capacitor bank is fully connected and only reactor is controlled? why not be vice versa?

  2. Francisco Alvarez
    May 12, 2015

    Good article. Keep’em coming!


  3. Dr. Mojtaba Noroozian
    Feb 15, 2014


    Do you have any experience for developing the software for SVC used for Arc Furnaces.

    Mojtaba Noroozian

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