FIELD: electrical engineering. SUBSTANCE: device is meant for use in supply mains rated 6 to 35 kV. Known device that has two single- phase ground resistors, zero-sequence current filters, two current transformers, potential transformer, two commercial-frequency filters, phase- shifting unit, three comparators, current sensor, AND gate, square-to- sawtooth pulse converter, pulse stretcher, delay circuit, serviceability check unit, and final element is provided, in addition, with third single-phase high- voltage ground resistor, three-phase power circuit breaker and disconnecting switch, ground-resistor control unit, third current transformer inserted in high-voltage ground-resistor circuit, and protective device for ground resistors; set of ground resistors is connected to collecting buses through circuit set up of circuit breaker, disconnecting switch, and set of current transformers; main input of ground-resistor control unit is connected to potential transformer output and additional inputs are used as inputs of control signals; outputs of ground-resistor control unit are connected to respective control inputs of circuit breaker; delay circuit input is connected to output of pulse stretcher and its output, to final element input. EFFECT: enlarged functional capabilities. 10 dwg
