ABSTRACT
Most of the relays discussed have depended on fundamental frequency voltages and currents for correct operation. A fault increases current magnitude and decreases voltage magnitude and changes the phase shift between them. The fault also causes transients or noise, such as dc offset, harmonics, distortion in the electrostatic and magnetic fields surrounding the power system element, traveling waves, etc. Transients may lead to relay malfunction, where the relay is assumed to be fed only with sinusoidal quantities. Thus, any event or fault-generated noise needs to be removed or filtered from the relaying voltages or currents and then fed to the relay.
