G - Physics – 01 – R
Patent
G - Physics
01
R
324/35
G01R 11/40 (2006.01) G01R 29/16 (2006.01) H02H 3/08 (2006.01) H02H 3/34 (2006.01)
Patent
CA 1101066
PROPORTIONAL GROUND CURRENT RELAY ABSTRACT OF THE DISCLOSURE The minimum instantaneous voltage output of a phase resistor connected to receive the rectified phase and neutral currents of three wye-connected current transformers, each magnetically coupled to respective phase conductor of a three phase electric power circuit, is proportional to the peak current of the phase conductor carrying the center magnitude phase current. A voltage proportional to this minimum instantaneous voltage is measured and stored by a capacitor each cycle. The peak instantaneous voltage output of a ground resistor connected to receive the full wave rectified output of three, parallel-connected current transformers, each also coupled to a respective phase conductor of the power circuit, is proportional to the peak ground current of the electric power circuit. A voltage proportional to the voltage output of the ground resistor is applied to the base of a NPN transistor, and the voltage stored by the capacitor is applied to the emitter of this transistor, to turn on this transistor every time the peak ground current exceeds a preselected percentage of the center magnitude phase current. The momentary turnon of this transistor at least once every current cycle activates a timing circuit, which after a predetermined time, initiates tripping of a circuit interrupter.
310299
Mcgraw-Edison Company
Pascal & Associates
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