A New Electronic Control Method to Suppress Ferroresonance Overvoltage in CVTs

Ferroresonance Supression Circuit (FSC) is the most important equipment used in Capacitor Voltage Transformer (CVT) for suppression of ferroresonance phenomenon. There are three types of FSC: active, passive and electronic type. This element is installed at the secondary side in parallel with CVT burden. In this paper, a new control unit is proposed for fast supression of oscillations and overvoltages due to ferroresonance occurrence. The proposed control unit takes samples from CVT output voltage and then triggers SCRs according to level of overvoltage. Moreover, the SCRs are turned off in the absence of overvoltage. By using this control unit, phase detector unit, firing circuit and separate source for firing the SCRs are not required. Unlike some previously proposed methods, the SCRs are not trigerred on for a prespecified time interval (typically 80 ms) but the SCRs turn-on time depends on the level of ferroresonance overvoltage. Simulation results show that the proposed control unit has desirable stability and fast response. Besides, the proposed control unit has not negative effect on frequency and CVT transient responses.