Shunt Reactor Function, Calculation, and Compensation

What is Shunt Reactor

A shunt reactor is a piece of electrical equipment used in high voltage power transmission systems to stabilize the voltage during load variations. A traditional shunt reactor has a fixed rating and is either connected to the transmission line all the time or switched in and out depending on the load.

A three phase shunt reactor is generally connected to 400KV or above electrical bus system for capacitive reactive power compensation of the power system and to control dynamic over voltage occurring in the system due to load rejection.

The shunt reactor should be capable of withstanding maximum continuous operating voltage (5% higher the rated voltage in case of 400 KV system) under normal power frequency variation without exceeding the top spot temperature of 150oC at any part of the shunt reactor.

The shunt reactor should be of gapped core type or magnetically shielded air core type. Both of these designs help to maintain the impedance of the reactor fixed. The impedance should be maintained at a constant value for avoiding harmonic current generated due to the system over voltage.

The shunt reactor has mainly core losses during its normal operating condition. So, care should be taken for minimizing the core losses during design.

Measurement of Losses in Shunt Reactor

We should measure the losses of a shunt reactor at rated voltage and frequency. But for very high voltage shunt reactor, it may be difficult to arrange such a high test voltage during measurement of losses. This difficulty can be overcome, by measuring the losses of the shunt reactor at any voltage lower than the system voltage of the reactor. Then this measured loss is multiplied by the square of the ratio of rated current to the current of the reactor at applied reduced test voltage to obtain the loss at rated voltage.

As the power factor of the shunt reactor is very low, loss measurement of shunt reactor by conventional wattmeter is not very reliable, instead of bridge method of measurement may be adopted for better accuracy.
This test can not segregate the losses in various parts of the reactor. To avoid, correction of test result for a reference temperature, it is preferable to take the measurement when the average temperature of the winding becomes equal to the reference temperature.

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