METHOD OF CORRELATION PROTECTION OF THREE-PHASE NETWORK WITH ISOLATED NEUTRAL FROM SINGLE-PHASE EARTH FAULTS Russian patent published in 2020 - IPC H02H3/16 

FIELD: electrical engineering.

SUBSTANCE: use in the field of electric power engineering for protection of electric networks 6–35 kV with isolated neutral from single-phase earth faults (SPEF). According to the method of correlation protection of three-phase network with isolated neutral from single-phase earth faults (SPEF) zero-sequence voltage is measured on buses common for connections, as well as zero-sequence currents in connections and voltage of their phases, detecting occurrence of SPEF by increasing zero-sequence voltage on common busbars above preset value, detecting the damaged phase by reducing the phase voltage of common busbars below a predetermined value, circuit is formed for short-time flow of double-fault current to earth by forced earthing through current-limiting resistor of one of two undamaged phases of common buses and current is measured in resistor. Note here that absence of double earth fault mode in network with zero-sequence voltage increase on common busbars is controlled. Signal for disconnection of connection with SPEF is generated by correlation ratio of values of emergency components of zero sequence currents generated in electric circuits of three-phase group of current transformers of each of connections with current in resistor. In currents of zero sequence of connections and current in resistor emergency components are selected by subtraction from current value of current of its one-stage value at previous period of industrial frequency, samples of zero-sequence residual current components of each of the connections with the corresponding samples of emergency component of current in the resistor are multiplied in pairs, absolute values of obtained products are accumulated and summed at interval of one period of industrial frequency. Maximum value is determined among the found sums, from which connection with SPEF is determined.

EFFECT: high selectivity and sensitivity of the protection action at SPEF.

2 cl, 2 dwg