Pilot-wire protection of transmission lines

THE PRESENT pilot-wire protective systems for transmission lines employing leased pilot-wire circuits are an outgrowth of conventional differential protective systems for other types of electric apparatus. Thus, these line-protective systems are characterized by the fact that the pilot wires are part of the differential connection between the current transformers at the line ends. The pilot wire has distributed shunt capacitance as well as series resistance, with the result that when these parameters reach sufficient magnitude, attenuation and undesirable phase shifts occur in the pilot-wire circuit. Thus, the system may be prevented from functioning correctly under certain operating conditions.