Square D Company

Robert J Erger

Kon B Wong

David Joseph Dunne

Charles D Bettis

A circuit breaker and method for interrupting the flow of electric current in a line includes connecting separable contacts to a conductor in the circuit. An actuating device, actuated by an activating signal, is connected to the separable contacts to effect separation of the contacts wherein the flow of electric current in the circuit is interrupted. A current sensor, such as an iron core current transformer, senses the current in the circuit to provide a first sinusoidal signal. A bridge rectifier is connected to the current sensor wherein the first sinusoidal signal is converted to a rectified signal and power is derived from the rectified signal. An interface circuit connected to the rectifying network converts the rectified signal into a second sinusoidal signal for providing the activating signal to the actuating device at a predetermined magnitude of the first sinusoidal signal. The interface circuit includes generating a sign bit indicative of the polarity of the first sinusoidal signal. A switch, such as a complimentary metal-oxide silicon (CMOS) switch, generates a positive half-wave rectified signal and a negative half-wave rectified signal from the rectified signal and the sign bit. The negative half-wave rectified signal is inverted and the positive half-wave rectified signal and the inverted negative half-wave rectified signal are summed and level shifted relative to the magnitude of the first sinusoidal signal to generate a second sinusoidal signal in phase with the first sinusoidal signal.

Circuit breaker including interface to convert a rectified signal to a

A system for detecting arcing faults in a line conductor carrying an electrical current between a power source and a load, the electrical current defining an AC waveform comprising a series of alternating positive half cycles and negative half cycles. In one embodiment, the method comprises the steps of obtaining current samples in a series of half cycles of the waveform, determining the peak current of each of the half cycles, and comparing the peak currents to determine changes in slope between half cycles. The number of changes in slope occurring within a selected time interval are counted and an arc indicative signal is produced when the number of reversals in polarity in slope occurring within the selected time interval equals or exceeds a predetermined threshold number. In another embodiment, the method comprises, in addition to the steps above, the steps of normalizing each of the current samples and autocorrelating the normalized current samples to obtain a measure of significant waveform shape changes between consecutive half cycles. Both the number of changes in slope and the number of significant waveform shape changes occurring within a selected time interval are counted and an arc indicative signal is produced when the number of reversals in polarity or the number of waveform changes equal or exceed predetermined threshold values.

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Cedar Rapids, IA, United States of America

Robert J Erger