PHASE RELAY FOR AC POWER TRANSMISSION LINE PROTECTION

摘要

A phase relay utilizes improved polarizing (VPOL) and operating signals (VOP) in order to provide discrimination between internal faults within a protected zone of an AC power transmission line and external faults that can appear as internal faults due to transients induced by capacitive voltage transformers or series capacitors. A zero sequence restraint signal is used to block operation of the phase relay on close-in single line to ground faults. A filter (76) is used in a by-pass circuit to attenuate high frequency transients which might delay, and possibly prevent a trip output on an internal fault. A high set by-pass circuit (72, 78), including zero suppression (72) to preclude an output on an external fault, is employed to provide faster operating times on severe internal faults. Forward offset and/or zero suppresion of the polarizing signal is used to reduce the characteristic timer setting and therefore increase the speed of the phase relay operation.