Mitigating the Impacts of CCVT Subsidence Transients on the Distance Relay

This paper presents a comprehensive time-domain model of the coupling capacitor voltage transformer (CCVT) to investigate the effect of CCVT subsidence transients on the distance relay. The studies show that voltage-zero subsidence transients can adversely impact the performance of the distance relay and result in the overreach problem. This paper also introduces a new approach to mitigate the effect of CCVT voltage-zero subsidence transients on the distance relay. The method is based on improving the degree of accuracy of the voltage phasor estimation during the CCVT subsidence transients. The proposed method is not affected by harmonics and high-frequency transient distortions of the voltage, and prevents the relay overreach problem even under high source impedance ratio (SIR). Moreover, the proposed method noticeably decreases the close-in fault clearance time under low SIR conditions, based on a fast current phasor estimation approach. The reported studies are conducted in the PSCAD/EMTDC software environment.