Static VAR Compensator (SVC)

Static VAR Compensator (SVC)

The static VAR compensator also known as SVC. The static VAR compensator is a shunt compensator FACTS device. The SVC is a generator or absorber which used to exchange the capacitive and inductive current from the power system.

In this way, it can control and maintain a specific parameter of the system. The SVCs can draw reactive power from the line and improve stability, control over-voltage, reduce voltage flickering and regulate voltage.

It has a capacitor bank fixed or controlled (switched) or fixed capacitor bank and switched reactor bank in parallel. The thyristors used to control and switching (on & off) of capacitor and inductor. So, it also known as static VAR switches because it uses switching for VAR control.

For stepwise control of the capacitor and reactor, thyristors in antiparallel connections are used. In this device, the capacitor and reactor unit act as continuous variables in the power system, this can be done by controlling of firing angle of thyristors.

There are four schemes for static compensation;

  • Saturated Reactor
  • Thyristor controlled reactor (TCR)
  • Thyristor-switched capacitor (TSC)
  • Combined TCR and TSC compensator

SVC placed to solve below problems in power system;

  • Voltage flickering caused by varying high reactance load like arc furnace
  • Transient stability limit
  • Power transfer capacity of the transmission line
  • Temporary overvoltage in the transmission system
  • Regulate the voltage
  • To improve power quality

The SVCs placed near high and rapidly varying loads in industries like arc furnace.

Saturated Reactor

The saturated reactor is a constant voltage reactive source. This is not very flexible with respect to the operating characteristic. This is nothing but a multi-core reactor and the phase winding is arranged to cancel the principal harmonics.

Thyristor Controlled Reactor (TCR)

It consists of a six-pulse or twelve pulse thyristor-controlled reactors and a fixed shunt capacitor bank. By adjusting the firing angle of the thyristor, the reactive power can control. The control system consists of a voltage and current measuring devices.

Filters used to provide fixed reactive power and absorb the harmonic current generated by TCR. The TCR used to continuous control of the electrical power system.

Thyristor Switched Capacitor (TSC)

It consists of a thyristor-switched capacitor bank. This capacitor bank is split into a number of units to achieve a stepwise control.

All the units have an equal rating. By full or zero conduction operation of the thyristor valve, the effective resistance of TSC can be varied in a stepwise manner.

For effective reactance calculation, we have to consider a fully connected or fully disconnected capacitor.

Combined TCR and TSC Compensator

A continuously variable reactive power can achieved by using a TCR in combination with TSC. A continuous change in the control order from fully lagging to a fully leading current obtained by this combination.

By using a different combination, an SVC can get various requirements to absorb/supply reactive power from/to the power system.

Advantages of SVCs

  1. It gives fast response to change in power system
  2. Less costly, high capacity, faster and more reliable
  3. It reduces harmonics and voltage fluctuations
  4. It provides load balancing function

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