ARC fault detector responsive to average instantaneous current and step increases in current and circuit breaker incorporating same
First Claim
1. An arc fault detector for an ac electrical system having a fundamental frequency and subject to arc faults generating step increases in an instantaneous value of current each time an arc is struck, comprising:
- a current detector comprising an average instantaneous current generator generating a running average of said instantaneous value of current; and
an output signal generator generating an arc fault signal as a function of said running average instantaneous current in excess of a threshold.
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Accused Products
Abstract
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.
55 Citations
21 Claims
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1. An arc fault detector for an ac electrical system having a fundamental frequency and subject to arc faults generating step increases in an instantaneous value of current each time an arc is struck, comprising:
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a current detector comprising an average instantaneous current generator generating a running average of said instantaneous value of current; and
an output signal generator generating an arc fault signal as a function of said running average instantaneous current in excess of a threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A circuit breaker for interrupting current in an ac electrical system having a fundamental frequency and subject to are faults generating step increases in an instantaneous value of said current each time an arc is struck, comprising:
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separable contacts;
an operating mechanism opening said separable contacts in response to a trip signal; and
an arc fault detector comprising;
a current detector comprising an average instantaneous current generator generating a running average of said instantaneous current; and
trip signal generator generating a trip signal as a function of said running average of said instantaneous current in excess of a threshold. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21)
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Specification