FIELD: electrics.
SUBSTANCE: current of zero line sequence is formed by commutation of one earthing resistor section by unidirectional thyristor key by industrial frequency half-period part at modulation interval of damaged line search duration equal to integer number of neutral shift voltage periods. Momentary values of line currents and earthing resistor current are monitored, at the moment of thyristor key launch the increments of indicated currents are registered, compared, and at increment coincidence a first indication of line damage is registered; simultaneously average positive and negative values of zero line sequence current are measured or calculated for full industrial frequency period, compared, and at positive current exceeding negative current value second indication of line damage is registered; further, final registration of line damage is performed only if both first and second damage indications are present in the search duration interval.
EFFECT: enhanced protection selectivity and reliability.
5 cl, 3 dwg
