Minimizing the Impact of Transients of Capacitive Voltage Transformers on Distance Relay

Transient response of coupling capacitor voltage transformers (CCVT) can result in malfunctions of fast impedance relays such as overreaching, underreaching or direction errors. Detailed model of a practical CCVT is used in this paper for simulation of input source error of the distance relay caused by the transient response of the CCVT. This paper describes an improved phasor estimation technique based on least squares method for estimation of voltage and current phasors in distance relays. The method minimizes the impact of transient oscillations of the CCVT output voltage on operation of distance relay during faults. The algorithm performance is evaluated during various fault conditions. The proposed method provides higher tripping speed for close-in faults in addition to solving the overreaching problem for systems with high source to line impedance ratio (SIR).