Disturbance performance improvment of distance relay with aid of wavelet

The present work deals with design of three-phase distance relay using wavelet multi-details transform technique. This technique is used to the fragment signal to details signals. The frequencies of those fragmented signals depend on the sample frequency. The energy levels of these chosen details are calculated for the three phase currents. Those are used to detect and to distinguish fault cases from other disturbances. On spite of identify the nature of fault. The apparent impedance as a vector has been calculated and then compared with setting impedance using the same technique. 400kV northern region network is taken as an example for application. MATLAB 7.2 is used for representation of the system. The results show that the relay responds to the faults with high speed and accuracy and distinguishes faults from other disturbances as well as identifies the type of fault. A trip signal to the circuit breaker issued after 20 milliseconds from the moment of fault.