ABSTRACT
All protective devices must remain constantly alert for faults and take appropriate action. Faults may take place, perhaps, only once in 10 years, but the relaying has to remain operational and ready. Hence routine testing (both steady-state and dynamic) is necessary. In steady-state testing the relay inputs (currents, voltages or combinations) are purely sinusoidal and the relay response is checked. In dynamic testing the sinusoidal inputs are superimposed with dc offsets and harmonics. The response is again noted. Needed for testing are steady-state test benches, dynamic test benches and routine maintenance.
