Ground fault detection circuit
AssigneeSquare D Company
InventorsEdward L. Nichols, III, Edward A. Harrison
Life of this patent
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Abstract
A current monitoring circuit of a ground fault detector which receives its input from the secondary winding of an annular core transformer through which extends the current carrying leads being monitored. A resistor and capacitor are connected in series between the secondary winding and an AC amplifier to form an RLC band pass filter to minimize the circuits sensitivity to noise outside of the band of frequencies of interest. The sensitivity of the circuit to temperature changes due to fluctuations of the inductance is reduced by choosing an inductance value sufficiently high to ensure that it is not reduced to below a critical level at which sensitivity is effected.
Claims23
A ground fault detection circuit comprising:
- means including an amplifier for producing a sensing signal in response to ground fault current exceeding a preselected value;
- and
- a band pass filter including a series RLC circuit coupled to the input of the amplifier for providing a frequency response to said sensing signal producing means to minimize sensitivity to noise in selected portions of the frequency spectrum.
An amplifier circuit comprising:
- a transformer of selected inductance coupled to an input current carrying circuit;
- an amplifier for producing a voltage output signal proportionate to said input current;
- means including a series RLC filter comprised in part of said inductance for coupling said input current to said amplifier and for establishing a selected frequency response for the circuit;
- and
- means associated with said transformer for establishing a selected inductance level for said filter of sufficient magnitude to insure that temperature related to fluctuation of the inductance level will not substantially affect the sensitivity of the circuit.
Dependencies are inferred from the claim text.