FIELD: relay protective gear for power transmission lines. SUBSTANCE: protective gear has three parallel circuits each incorporating current adder, threshold element and OR gate, time relay whose input is connected to OR gate output and output, to threshold element input; novelty is introduction of three current increment sensors, three inverters, and three AND gates; output of each adder is connected to input of respective current increment sensor whose output is connected to input of respective threshold element; output of each threshold element is connected through respective inverter to input of respective AND gate and to one of inputs of two other AND gates; output of each AND gate is connected to input of OR gate. EFFECT: enhanced sensitivity ensuring reliable backup protection of traction substations. 9 dwg
