The introduction of Static var compensator

Static var compensator (SVC) rose in the 1970s and has developed into a very mature facts device. It is widely used in load compensation and transmission line compensation of modern power system. In high-power power grid, SVC is used for voltage control or other benefits, such as improving system damping and stability. This article will briefly introduce the Static var compensator.

The following is a list of contents

• Introduction of Static var compensator

• Principle of Static var compensator

• Type of Static var compensator

• Static var compensator compared with power capacitor

Introduction of Static var compensator

Static synchronous var compensator is the most advanced reactive power compensation device. It no longer uses high-capacity capacitors and inductors to generate the required reactive power, but realizes the qualitative leap of reactive power compensation technology through the high-frequency switch of power electronic devices. It is especially suitable for dynamic reactive power compensation in medium and high voltage power system.

Static var compensator is a fast, smooth and controllable dynamic reactive power compensation device without rotating parts. It uses controllable reactors and power capacitors (fixed or group switching) in parallel. The capacitor can emit reactive power (capacitive), and the controllable reactor can absorb reactive power (inductive). By adjusting the reactor, the whole device can change smoothly from sending reactive power to absorbing reactive power (or reverse), and the response is fast.

Principle of Static var compensator

Static var compensator is a power quality control device that controls or switches passive power components by controlling the conduction angle of thyristor. According to the different control and switching elements, it can be divided into thyristor controlled reactor (TCR), thyristor switched reactor (TSR), thyristor switched capacitor (TSC), thyristor switched filter (TSF) and other types. In principle, there is no difference between low-voltage static var compensation and high-voltage var compensation, but in the implementation mode, the centralized compensation is changed to decentralized compensation, and the high-voltage compensation is changed to low-voltage compensation.

Type of Static var compensator

According to the regulation method of reactor, Static var compensator has the following three types.

Controllable saturation reactor type

The controllable saturable reactor consists of two parts of windings, namely AC winding and DC control winding. The inductance of AC winding can be changed by changing the excitation current of DC control winding and adjusting the saturation degree of iron core.

Self saturating reactor type

When the self saturation reactor is at a certain voltage value, the iron core will be self saturated. The reactance value is large when it is unsaturated and small after saturation. With the change of reactance value, the absorbed reactive power will change.

Phase controlled reactor type

The thyristor switch is used to control the on time of the reactor, so as to control the waveform of the current in the reactor. The fundamental current will change with the conduction angle, which is equivalent to changing the reactance value of the reactor.

Static var compensator is widely used in low-voltage power supply and distribution system to adjust voltage, improve voltage level, reduce voltage fluctuation, improve power factor, suppress voltage flicker and balance asymmetric load. The filter matched with Static var compensator can absorb harmonics and reduce harmonic interference. In EHV transmission system, the function of Static var compensator is to provide reactive power compensation, adjust voltage, improve system voltage level, improve power system dynamic and transient stability, suppress power frequency overvoltage and so on.

Static var compensator compared with power capacitor

Static var compensator can adjust continuously and smoothly in both directions; Compared with the synchronous condenser, the Static var compensator has no rotating parts, so the operation and maintenance are simple. At the same time, the Static var compensator has fast regulation speed, so it has great advantages. Its disadvantage is that it generates harmonics. If no measures are taken, it will pollute the power system. Generally, there is a supporting power filter. In order to realize bidirectional continuous regulation and overcome the weakness of shunt capacitor regulation effect, it is required to increase the compensation capacity.

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