Reactor Switching

Shunt Reactor Switching

Shunt reactors are used to regulate the reactive power balance of a system by compensating for the surplus reactive power generation of transmission lines or cables. This surplus reactive power is present when lines are lightly loaded or there is a sudden drop in load due to a failure somewhere in the system. Additionally, a shunt reactor switch can regulate excessive voltage rise (Ferranti Effect) created on long lines that are lightly loaded.

How Do I Know if a Shunt Reactor is Right For Me?

Shunt reactors are most often utilized on long power transmission lines with system voltages of 220kV and above. Shunt reactors may also be needed for system voltages of 100kV or more and even on large urban networks to prevent excessive voltage rise when there is a significant decrease in system load.
A shunt reactor may need to be switched multiple times a day as load on the lines increase and decrease. If the load on the line increases (decreasing the voltage) the reactor must be switched off or disconnected from the line. As the load lessens and the voltage starts to rise again, the shunt reactor must be switched on or connected back onto the line. Successful switching of shunt reactors is critical for maintaining the desired system power factor and for keeping voltages at a safe level for all connected equipment throughout the system, either from a substation or control center.

How To Keep Your Shunt Reactor Operating At Full Capacity


Switching shunt reactors is a unique duty. The small continuous currents, typically 300 A or less, are relatively easy to interrupt for modern interrupting devices such as circuit breakers and circuit switchers. What makes switching the shunt reactor unique is that when the current is extinguished, the shunt reactor voltage oscillates toward zero at the reactor natural frequency (1 to 5 kHz). Since the system supply voltage is at 60 Hz, the high frequency of the reactor causes the reactor voltage to rapidly depart from the system voltage, thus creating a steep and high magnitude TRV. This high/fast TRV will cause the interrupter to reignite until there is sufficient contact gap to sustain complete interruption. These potentially high energy re-ignitions can be stressful to the shunt reactor, causing turn to turn overvoltages, resulting in premature failure of the shunt reactor and the switching device.

Several switching techniques have been developed by manufacturers in an attempt to minimize the frequency, magnitude, and impact of these re-ignitions including controlled voltage switching devices, modified interrupter designs, and the addition of voltage arresters or capacitors.

Need A Shunt Reactor – What Can Southern States Do For Me?

In 2008, Southern States, a high voltage switch manufacturer, introduced the only switching device designed specifically for reactor switching, the RLSwitcher®. The RLSwitcher® interrupter is unique in that it is designed to deliberately delay interruption for the first couple of zeros. This is followed by a transition region where it will try to interrupt but may experience a low energy reignition. When the contacts are sufficiently opened, the interrupter completely clears. The result is a “clean” interruption with no high energy re-ignitions. This “clean” interruption results in an extended life of both the switching device and shunt reactor.

If you are looking for more information regarding shunt reactors and the benefits of switching with the Southern States RLSwitcher®, give us a call at 770-946-4562 today!

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