METHOD AND DEVICE FOR DIRECTIONAL PHASE-FAILURE GROUND-FAULT PROTECTION OF AC DISTRIBUTION NETWORK Russian patent published in 2007 - IPC H02H3/16 

FIELD: selective phase-failure ground-fault protection of power networks with arbitrarily connected neutral.

SUBSTANCE: proposed method involves detection of too high first half-wave amplitudes in high-frequency components of zero-sequence current and voltage exceeding reference value. Phase shift between them is measured as soon as high-frequency current crosses zero, Phase shift equal to or about 90 deg. is recorded during check interval. Then low and maximal admissible amplitudes of zero-sequence voltage low-frequency component is checked. Assumed as maximal admissible amplitude of low-frequency component is maximal short-time shift of neutral admissible for particular line. Assumed as low-value of low-frequency component amplitude is continuous maximal level of neutral shift admissible for particular line. Low-frequency component amplitude is checked for excess above low value under check. If result is adequate, low-frequency component amplitude is measured during check interval. Alarm signal is generated upon recording of excess value in time interval specified including time period of high-frequency transients on occurrence of phase-failure ground faults, time taken to compensate for capacitive currents on occurrence of phase-failure ground faults, and time required to tune away noise and self-eliminated phase-failure ground faults. Device implementing proposed method has high-frequency current and voltage channels and low-frequency zero-sequence voltage channel, phase-sensing element, control circuit, four delay shapers, phase detection result clear unit, and alarm signal generating circuit.

EFFECT: enhanced reliability and selectivity, reduced malfunction probability.

6 cl, 4 dwg