Portable ground fault detector

Details Portable ground fault detector Portable ground fault detector

1992-10-30

1994-11-08

Snow, Walter E.

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of ground fault indication

324509, 324551, 340650, 361 31, G01R 3102

Patent

active

053630475

ABSTRACT:
Disclosed is a ground fault detection apparatus for an operating, normally ungrounded supply system, the apparatus having a periodically grounded center tap of a test impedance that is connected across conductors of the system, and detector circuitry including a charge balance circuit having low gain and wide dynamic range that measures the amplified voltage output of a Hall effect current sensor. A preferred implementation of the circuit has a charge transfer variable oscillator. A pair of microprocessor-controlled counters that are responsive to the oscillator precisely measure the average frequency of the oscillator over intervals that are automatically maintained at approximately one second in duration, the microprocessor calculating the fault current as the difference between current measurements taken with and without the center tap grounded. The apparatus has sufficient dynamic range for directly measuring system currents on the order of 100 A, while reliably detecting leakage currents in the milliampere range.

REFERENCES:
patent: 3857070 (1974-12-01), Smith
patent: 4368498 (1983-01-01), Neuhouser
patent: 4739274 (1988-04-01), Kimball et al.
patent: 4739275 (1988-04-01), Kimball et al.
patent: 4837519 (1989-06-01), Lopetrone et al.
patent: 4929901 (1990-05-01), Kimball et al.
patent: 5014043 (1991-05-01), Lopetrone et al.

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