METHOD FOR DETECTING GROUND FAULT IN INSULATED- NEUTRAL THREE-PHASE SUPPLY MAINS Russian patent published in 2000 - IPC

FIELD: power engineering. SUBSTANCE: method is used to detect ground fault in underground mains rated up to 1140 V. Phase failure is detected by coincidence of two results. Both results are updated once within complete phase of zero-sequence voltage variation but at relative shift of 180 deg. In total, frequency doubling of result obtained in ensured. First and second results are determined by detecting correspondence of noninverted and inverted zero-sequence voltages to first and second reference phase intervals of initial phase. First reference phase interval is set to be not over 120 deg. , second one, to equal first interval in magnitude and shifted from the latter through 180 deg. Results are considered true provided two zero transmissions of zero-sequence voltage coincide during their repetition interval. Results are determined by signal indicating hazardous ground leakage shaped at time delay in response to increase in zero-sequence voltage. In some cases, delay time is set as decreasing function of zero- sequence voltage. EFFECT: improved reliability of ground fault detection dispensing with its validity check; improved speed of serious fault detection at adequate noise immunity. 2 cl, 4 dwg