Electromagnet relay with flux biasing

A rotating disc electromagnetic relay has an operating element which applies a torque to the disc tending to close the main contacts and a restraint element generating a torque which together with a spring tends to open the relay contacts. The operating and restraint elements each have an E-shaped core defining two magnetic circuits with a common center leg. Two voltages to be compared are applied to two input coils on the center leg of each element in the same sense to generate a flux representative of the sum of the voltages in the operating element and in the opposite sense to produce a flux representative of the difference between the two voltages in the restraint element. The flux in the common leg of each element divides between the two magnetic circuits. The flux in one magnetic circuit of each element is shifted in phase by a first lag coil on an outer leg of the core to generate the opening and closing torque, respectively. A second lag coil on one leg of one element is selectively shunted to increase the net closing torque by contacts of a shunt relay energized by closure of the main relay contacts. Preferably, the additional lag coil is provided on the outer leg of the second magnetic circuit of the operating element and is shunted by normally closed contacts.