Abstract: An abnormality detection circuit detects abnormality relating to ground fault in secondary winding circuitry of transformer, non-grounding fault of transformer assembly casing or false connection of the AC power source to the transformer assembly in reverse polarity. An interrupter circuit turns a switch off in response to detection of the abnormality by the abnormality detection circuit to interrupt the supply of the AC power to the transformer. When the supply of the AC power is interrupted, the switch is connected to a restart circuit, whereupon the circuit is activated to allow a charging current to flow to a capacitor, which is connected in series in a drive current path of a drive circuit with a time delay on the order of 0.5 to 1.0 second which is determined by a delay circuit thereof. The charging current drives a restoring circuit, which controls the interrupter circuit to its restoring condition temporally so that the switch is turned to its “on” condition only once.

Abstract: An abnormality detection circuit 22 delivers a detected abnormality relating to a transformer 11. An interrupter circuit 23 turns a switch 16 off to interrupt the supply of the power to the transformer 11. When the supply of the power is interrupted, the switch 16 is connected to a restart circuit 31, whereupon the circuit 31 is activated to allow a charging current to flow to a capacitor, which is connected in series in a drive current path of a drive circuit 32 with a time delay on the order of 0.5 to 1.0 second which is determined by a delay circuit thereof. The charging current drives a restoring circuit 33, which controls the interrupter circuit 23 so that the switch 16 is turned on.