Ground-fault detector using square hysteresis loop reactor core

Claim 1

A ground-fault detection circuit comprising, in combination: a core of square hysteresis loop material; biasing winding means, output winding means, and first and second control windings wound on said core; said first and second control windings having respective first terminals connectable to a power source and having respective second terminals connectable to opposite sides of a load circuit which is to be monitored for a ground-fault condition; said first and second control windings being wound to generate opposing magnetomotive forces within said core when said first and second windings conduct current between said first terminals and a load circuit; said biasing winding means being energized by connecting first and second input terminals thereof to a power source, with said first input terminal being connected to said first terminal of said first control winding; an output signal generating means; said output winding means having output terminals connected to said output signal generating means; said output winding means having a first relatively low voltage level induced therein by the magnetizing force of said biasing winding when the magnetizing forces generated by load currents in said first and second control windings are equal and opposite; said output winding means having a second relatively high voltage level induced therein when the current through said first and second control windings differ by a ground-fault current having a relatively small magnitude; said output signal generating means being operative responsive to the development in said output winding means at and above said second voltage level, and being inoperative when the output of said output winding means is at said second voltage level.