The Shunt Reactor is a consumer of reactive power. In some applications there is a need to consume the inductive reactive power in steps. In such a case, several shunt reactor units are needed to connect and disconnect frequently which requires more circuit breakers and foot prints at substation. Instead of having several units, one unit that covers the entire power range could be an economical solution.
A Variable Shunt Reactor (VSR) is a reactor where the inductance can be varied in steps. The reactive power consumption can increase up to twice its initial value over the whole regulating range. The regulation speed is determined by the operation time of the tap changers used; and it is in the order of seconds. VSRs are based on the same concept as a Fixed Shunt Reactor. However, the design requires special attention and the VSR is considered as a separate product type.
Generally, when there is a slow variation of the load, the VSR works as an efficient reactive power compensator in order to fine tune the voltage in the system. VSRs provide dynamic reactive power compensation with the regulation range around 100% (e.g. 50-100 MVAr) and ratings up to 250 MVAr, 500 kV.