FIELD: electrical engineering. SUBSTANCE: when the switching device is turned on, thyristor 8 comes into action, final-control relay 10 and time relay 19 are switched on. At the appearance of any voltage asymmetry in the network at the output of the voltage filter 3 of negative sequence, a voltage appears which is applied to resistor 20 in antiphase with the unlocking voltage on the controlling electrode of thyristor 8. Thyristor 8 is cut off, final-control relay 10 is switches off and breaks the feeding chain of coil 6 of the starter contactor with its contacts or locks the feeding chain of cut-off coil 7 of the automatic circuit breaker. Electric plant 1 is de-energized. The switching on of the switching device to the abnormal mode results in the fact that only time relay 19 comes into action and acts in much the same way as final-control relay 10. EFFECT: enhanced self-control of good condition. 1 dwg
