Dielectric Withstand Evaluation for Shunt Reactors due to Disconnect Switching Transients

Because of this application, shunt reactors are subjected to transient overvoltage caused by daily maneuvers due to their high inductance and current interruption phenomena. At some conditions, there is high probability of re-strikes (reignition of the arc after interruption of small inductive currents) during the opening process of the circuit breaker, which implies severe overvoltage imposed on the shunt reactor terminals, with its inherent fast front transient and frequency spectrum of hundreds of kHz. The long-term internal insulation withstand of the shunt reactor will depend on some characteristics of overvoltage stresses on their terminals such as, for example, the rate of rise of the voltage imposed by reignitions and its previous peak, frequency spectrum and finally the number of occurrences and related substation topologies, to be considered throughout the equipment lifetime.

The application of controlled switching technology in high-voltage circuit-breakers provides efficient mitigation of these undesirable effects but may not be available due to different factors during all switching operations, like fault clearance, for instance.

In this context, this paper proposes the evaluation of the transients caused by switching events of circuit breakers connected to reactive load and their impact on dielectric design of shunt reactor design 550 kV, 164.7 MVAr. It addresses the effects and importance of appropriated shunt reactor modeling into system studies and possible mitigation methods. By using different reactor black-box modeling approaches provided by the manufacturer, the influence on system studies results is evaluated under a statistical approach for long term reliability. The voltage stresses are compared to standard tests regarding the concepts of severity factor in the frequency domain.

The concept of reliability factor proposed by the manufacturer was considered to evaluate the long-term design insulation withstand. An alternative criterion based on the maximum and averages rates of overvoltage is also addressed.

The paper also presents a comparative study of connection topology and mitigation methods

(without and with RC filter) on transient voltage stress of vacuum circuit breakers connected to inductive load and its influence on recovery voltages based on experiments.