FIELD: relay protection of power transmission lines. SUBSTANCE: protective gear has compensating phase voltage shaper whose output phase leads are connected to inputs of resistor units shaping resistance and reactance components, shaper of voltage proportional to zero-sequence current whose output is also connected to inputs of units shaping resistance and reactance components whose first outputs are connected to inputs of respective multipliers and second ones, to inputs of adders whose outputs are connected to inputs of AND logic unit whose output functions as protective gear output, first and second reference voltage sources; second reference voltage is applied through three switches to second inputs of multipliers; first reference voltage is applied through second three switches to same inputs of multipliers; control inputs of first three switches are connected directly and those of second three switches through AND gates to first outputs of respective units shaping resistance and reactance components. EFFECT: improved sensitivity to single-phase ground faults through contact resistor. 3 dwg
