Ground fault circuit interrupter with immunity to wide band noise
First Claim
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1. A ground fault circuit interrupter for interrupting current in a protected ac electric system subject to wide band noise, said circuit breaker comprising:
- separable contacts interrupting current flow in said protected electric system when opened;
sensing means generating an ac sensor signal representative of ac current flowing from said protected electric system to ground;
trip signal generating means comprising amplifier means connected to said sensing means generating at an output an amplified ac sensor signal in response to said ac sensor signal and containing amplified wide band noise of a first polarity only, and comparator means connected to said output of said amplifier means and generating a ground fault trip signal only when said amplified ac signal is of a second polarity opposite said first polarity and exceeds a reference signal in magnitude; and
trip means responsive to said ground fault trip signal to open said separable contacts.
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Abstract
In a ground fault circuit interrupter in which it was found that wide band noise induced by load transients is rectified by an op-amp in the detector circuit, false trips due to the wide band noise are eliminated by only comparing the output of the amplifier with a threshold of opposite polarity to that of the rectified noise signal and by eliminating capacitive coupling between the current sensor and the op amp. This requires an op amp with a low offset, on the order of about five percent or less.
95 Citations
7 Claims
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1. A ground fault circuit interrupter for interrupting current in a protected ac electric system subject to wide band noise, said circuit breaker comprising:
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separable contacts interrupting current flow in said protected electric system when opened; sensing means generating an ac sensor signal representative of ac current flowing from said protected electric system to ground; trip signal generating means comprising amplifier means connected to said sensing means generating at an output an amplified ac sensor signal in response to said ac sensor signal and containing amplified wide band noise of a first polarity only, and comparator means connected to said output of said amplifier means and generating a ground fault trip signal only when said amplified ac signal is of a second polarity opposite said first polarity and exceeds a reference signal in magnitude; and trip means responsive to said ground fault trip signal to open said separable contacts. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification