A New Algorithm to Stabilize Distance Relay Operation During Voltage-Degraded Conditions

This paper deals with the possible operation of distance relays during impending voltage instability and presents a new method to prevent its maloperation in power system voltage-degraded conditions. The proposed method successfully discriminates between fault occurrence and system incidents during stressed voltage conditions, even for the most severe cases such as sudden equipment outages and high impedance faults. The proposed scheme successfully blocks maloperation of relay zone 3 where the degraded condition is detected. It is based on the rates of change of voltage and current magnitudes. These values are different during fault occurrences in comparison with the corresponding values during stressed conditions system incidents. Simulation results verify the effectiveness of the proposed method.