DC ground fault detecting apparatus with an auto-null circuit an

Details DC ground fault detecting apparatus with an auto-null circuit an DC ground fault detecting apparatus with an auto-null circuit an

1994-10-31

1996-06-25

Wieder, Kenneth A.

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of ground fault indication

324529, 324551, 324117H, 340650, 361 42, G01R 3102

Patent

active

055303633

ABSTRACT:
To locate ground faults in a normally ungrounded DC circuit a centertapped voltage divider is connected across the positive and negative buses. An oscillator controlled switch is connected between the centertap and ground which when operating modulates the ground fault currents with a square wave having a repetition rate no greater than 3 hertz. A Hall probe including a field nulling coil is clamped successively along the conductors under test. A capacitive storage circuit maintains the energization of the nulling coil at the level that provided a null indication immediately prior to actuation of a test button. The Hall probe is connected to a read-out oscilloscope which indicates the presence or absence of the square wave modulation. Fault currents as small as 1 ma can be detected.

REFERENCES:
patent: 3274489 (1966-09-01), Behr
patent: 3757169 (1973-09-01), Beresnikow
patent: 4528497 (1985-07-01), Arato
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: 4884034 (1989-11-01), Guzman
patent: 4929901 (1990-05-01), Kimball et al.
patent: 5363047 (1994-11-01), Dresti et al.

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