FIELD: relay protective gear. SUBSTANCE: device has corrected phase voltage shaping unit whose inputs are connected to line under protection and whose three outputs are connected, respectively, to first and, via respective phase shifters, second inputs of respective units shaping resistance and reactance components, unit shaping voltage proportional to zero-sequence current whose output is connected, respectively, to third and, through phase shifter, to fourth inputs of units shaping resistance and reactance components whose first outputs are connected through squarers to first inputs of respective multipliers whose second inputs are connected to reference voltage unit output; second outputs of units shaping resistance and reactance components are connected to second inputs of respective adders whose outputs functions as output of device. According to invention, device is provided, in addition, with three switches inserted between outputs of multipliers and first inputs of respective adders; control input of each switch is connected to first output of respective unit shaping resistance and reactance components. EFFECT: improved sensitivity to single-phase ground faults through contact resistance. 3 dwg
