DYNAMIC EVALUATION OF A HIGH-SPEED DIRECTIONAL OVERCURRENT RELAY

The design of a new high speed directional overcurrent relay is presented. The relay is more sensitive to the direction of fault current and issues high speed trip signal within one cycle time. The decisive signal is computed as the integral of product of the relay current and the derivative of its corresponding phase voltage over one cycle window. The directionality is determined by comparing this signal to a properly selected fixed threshold. The proposed design is examined in a cascaded lines power system with four relays. The good performance of the relays is verified for different fault types in different locations. The presented design is also evaluated for operation as an autorecloser. A modified design of the proposed relay is also manifested. It is based on cubed values of the relay input signals. It is shown that the modification accelerates the tripping speed to less than half a cycle.