FIELD: protection of electric circuits of synchronous machines against polarity reversal and asynchronous running. SUBSTANCE: device has junction current and voltage sensors connected so that their signals are in phase opposition at phase shift angle between current and voltage equal to zero; two half-wave rectifiers; two comparators; control circuit implementing multiple-valued function; novelty is introduction of pulse generator, pulse synchronizer, two electronic switches operating in phase opposition, inverter, current-to-voltage phase-shift counter, additional angle counter, state flip-flop, and output device. EFFECT: provision for checking polarity during each period of supply frequency and for response to angle of phase shift depending on digital module of counter only. 2 dwg
