Differential motor protective relay cct - has transformers in phase line coupled via rectifiers and RC ccts to cut-out trigger

摘要

The differential protective relay circuit for motors has a first transformer (1) connected into the motor phase line and a second transformer (2) in the neutral part of the phase line. The transformers secondaries are connected to two separate bridge rectifiers whose outputs are coupled via two RC circuits to the trigger (13) input. The output diagonals of the rectifiers are connected in parallel with a two-resistor voltage divider (9, 10) across them. The first RC circuit (7, 8) is connected with its capacitor across the whole divider and its output over a decoupling diode to the trigger, whilst the second RC circuit (11, 12) is coupled with its capacitor across one divider resistor and its output over a second decoupling diode to the trigger input.