DIFFERENTIAL RELAY Russian patent published in 2003 - IPC

FIELD: short-circuit protective gear for transformers. SUBSTANCE: differential relay has connected in series instrument transformer, rectifier unit, low-frequency filter, and first threshold unit; series-connected pulse counter, second threshold unit, and final element; clock generator; AND gate whose forward input is connected to HIGHER output of first threshold unit, second forward input, to clock generator output, and output, to pulse counter data input; OR gate; pulse shaper whose input is connected to LOWER output of first threshold unit and output, to first input of OR gate, output of the latter being connected to zero setting input of pulse counter; monostable multivibrator whose output is connected to second input of OR gate and to trigger input of clock generator; and third threshold unit whose input is connected to output of pulse counter and output, to inverting input of AND gate. EFFECT: enhanced precision and immunity to noise caused by heavy inrush magnetizing currents when turning on unloaded transformer. 2 cl, 2 dwg