Adaptive Distance Relay with Combined Polarizing Quantity Based on Compensated Voltage

Mho relay usually takes a single voltage as polarizing voltage such as positive sequence voltage.In this way,its operating boundary is fixed and operating characteristic cannot adapt to fault resistance.To enhance the adaptive capability against fault resistance,a second voltage quantity changing with fault resistance should be introduced to form a composite vector of multiple polarizing voltages that is able to track the trajectory of fault resistance.Hence this paper proposes a new composite polarizing voltage consisted of a part of compensated voltage and the primary polarizing voltage that is the pre-fault voltage at the location of the setting impedance.To overcome transient overreaching problem,a part of the primary polarizing voltage is also introduced to the compensated voltage to adjust the protective zone to fault clock.The paper investigates the operating characteristics of the adaptive distance relay in the voltage plane and the impedance plane.The performance of the relay has been demonstrated on a two-source 500 kV system with 300 km line.Theoretical analysis and simulation show that the relay has good resistive tolerance.