Adaptive Impedance Relay with Composite Polarizing Voltage

Fault resistance can bring some disadvantages for an impedance relay while a single-phase-to-ground fault occurs on transmission line. Taking advantage of the compensated voltage changing with fault resistance, this paper presents a kind of adaptive impedance relay with composite polarizing voltage to enhance the capability against fault resistance. On the other hand, the operating boundary of the adaptive relay may enter into "in-phase" region along with the increase of fault resistance. To prevent the adaptive relay from the "in-phase" problem, a new additional blocking component is proposed in this paper. Both the adaptive relay and the blocking component are all analyzed in the voltage plane and the impedance plane. Theoretical analyses show that both of them have circular characteristics with greater resistive tolerance. The performance of the relay has been demonstrated on a two-source 500 km line 750 kV system.