FIELD: protection equipment for electrical engineering. SUBSTANCE: device has serial circuit of zero sequence voltage detector, industrial frequency filter, voltage stepping up circuit and clock oscillator. Goal of invention is achieved by generator of clock pulses displaced by half period. Said generator is introduced into said circuit. In addition, each phase of power supply network has serial circuit of feeding phase voltage detector, reference pulse generator, synchronous D flip-flop, AND gate. Goal of invention is achieved by following members introduced into phase circuits: serial circuit of generator of clock pulses displaced by half period, and second synchronous D flip-flop are introduced between output of feeding phase voltage detector and second input of AND gate. Device provides separate detection of short circuited phases. Both results are updated for one complete period of zero sequence with relative displacement of half period. This results in possibility to double frequency of result production. EFFECT: increased stability to errors in detection of short circuited phase without time losses for validity check. 2 cl, 2 dwg
