METHOD FOR SINGLE-PHASE-TO-GROUND FAULT PROTECTION OF THREE-PHASE, INSULATED-NEUTRAL SUPPLY MAINS Russian patent published in 1998 - IPC

FIELD: electrical engineering; protection of supply mains as well as generators, motors, and transformers supplied with power from insulated-neutral mains. SUBSTANCE: method involves measurement of leakage current to ground through total mains- to-ground resistance, averaging of this current, calculation of insulation resistance from average value of measured current and supply voltage, its comparison with maximum permissible value, and generation of signal for disconnecting mains under protection as soon as it reaches maximum limit; in addition, phase with highest voltage to ground is selected to measure leakage current in it. Mentioned leakage currents are compared within present time interval corresponding to commercial-frequency period, and ground fault in insulation is located by their proportion. In addition, phase voltages are measured and total resistance of mains under protection to ground is determined by their relation to respective leakage current which makes it possible to locate ground fault at early stage of its development. EFFECT: enlarged functional capabilities and improved sensitivity of protective gear. 2 cl, 5 dwg