Ground fault detector

Claim 1

A ground fault detector device comprising: a zero phase-sequence current transformer, electrically connected to an electric circuit path which includes an electrically energized circuit interrupter, to detect a ground fault current flowing through the electric circuit path to provide an output current in response to the fault current; a half-wave rectifier for rectifying the output current from said transformer; a semiconductor switching element rendered conductive in response to said half-wave rectified output current from said zero phase-sequence current transformer; electromagnetic circuit means energized by a voltage in said electric path and responsive to the conduction of said semiconductor switching element to energize said circuit interrupter connected in said electric path to open said electric path; and circuit means including a resistor having a relatively high magnitude of resistance, a capacitor connected in cascade with said resistor and a constant voltage element having a voltage dependent impedance connected across said resistor, said circuit means applying through said resistor the half-wave rectified output current from said current transformer less than a predetermined magnitude to gradually increase a potential across said capacitor to a predetermined magnitude whereupon said semiconductor switching element is put in its conducting state to energize said circuit interrupter, said constant voltage element responding to the half-wave rectified output current from said current transformer in excess of the first-mentioned predetermined magnitude to instantaneously increase the current flowing to said capacitor to put said semiconductor switching element in its conducting state.