Eaton Corporation

Thomas Christopher Rae

Robert Tracy Elms

Thomas Edward Natili

An arc fault detector includes an average instantaneous current generator which averages the current over the fundamental period and produces a substantial output only where there are substantial variations in waveform between half-cycles which is indicative of an arc. To discriminate over inrush currents, a pulse generator generates a pulse in response to the step increase in current caused by striking of an arc. An output circuit generates an arc signal when the time attenuated accumulation of pulses occurring in half-cycles in which the average instantaneous current is above a selected threshold reaches a predetemiined level. To further discriminate over dimmers during turn on of a cold tungsten bulb, die ANDing with the average instantaneous current is delayed until a time attenuated accumulation of the pulses reaches a threshold value. The average instantaneous current can be approximated by a bandpass filter with a center frequency below the fundamental of the ac current. A second bandpass filter with a center frequency above the fundamental can be used as the pulse generator.

ARC fault detector responsive to average instantaneous current and step increases in current and circuit breaker incorporating same

An arc fault detector of the type which generates a trip signal when a time attenuated accumulation of pulses produced each time an arc is struck reaches a selected value, includes a pulse conditioner which discriminates against false trips induced by phenomena such as tungsten bulb burn out and turn on of a cold tungsten bulb controlled by a dimmer. The pulse conditioner includes a zener diode which limits the amplitude of the pulses applied to the integrator, and stretches all of the pulses to reduce the variation in pulse duration. The latter can be accomplished by a peak detector which stretches pulses which reach the zener limit to a duration of at least about a half cycle.

Arc fault detector with protection against nuisance trips and circuit

A circuit breaker with an arc fault circuit provides immunity to false trips caused by tungsten bulb burnout and by a cold tungsten filament energized through a solid state dimmer. The detector circuit includes a pulse generator which generates pulses in response to the step increases in current occurring each time an arc is struck. A zener diode limits the amplitude of pulses generated by the pulse generator to a value which is below that of pulses generated by the tungsten lamp. When a time attenuated accumulation of these pulses reaches a predetermined value, the circuit breaker is tripped. By clipping the pulses with the zener diode, the few large pulses generated by tungsten bulb burnout or energization of a cold tungsten bulb by a solid state dimmer switch are insufficient to allow the time attenuated accumulation of pulses to reach the trip value.

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Irwin, PA, United States of America

Thomas Christopher Rae