FIELD: protection of ac mains with insulated or compensated neutral, with neutral grounded through high-value resistor, or with fully compensated single-phase ground-fault current fundamental. SUBSTANCE: device is provided with series-connected clock generator and microprocessor unit, analog-to-digital converter, main and read-only storage units, address register, controller of storage units, and digital data unit all connected to microprocessor unit through system unibus interconnecting address register output and inputs of storage units, and switch which is connected through respective switches to threshold element and signal limiter, as well as control unit with relevant connections. Device records great amount of information about processes in supply mains on occurrence of single-phase ground faults. EFFECT: improved speed of response and validity of detection of fault (selective action) in transient and steady-state ground faults, improved reliability of device. 3 wdg , 1 tbl
