Arc fault detector comparing integrated interval to interval filtered load current and circuit breaker incorporating same
First Claim
1. An arc fault detector for an ac electrical system, said arc fault detector comprising:
- input means generating from current flowing in said ac electrical system a sensed current signal from which at least a fundamental frequency component has been removed;
integrating means repetitively integrating said sensed current signal over equal time intervals to generate integrated sensed current values;
comparing means comparing said integrated sensed current value for the most recently completed time interval with said integrated sensed current value for the immediately previous corresponding time interval to generate indications of interval to interval increases and decreases in said integrated sensed current values;
storing means storing said indication of interval to interval increases and decreases for a selected number of the most recently completed corresponding time intervals; and
output means generating an arc fault signal as a function of a count of changes between said indications of interval to interval increases and decreases for said selected number of most recently completed corresponding time intervals stored by said storing means.
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Accused Products
Abstract
Arc faults are detected by bandpass filtering the current to generate a sensed current signal with a pulse each time an arc is struck. A resettable integrator integrates this sensed current repetitively over equal time intervals such as each cycle of the ac current. The integrated value of the sensed current is compared with the value for the previous corresponding time interval stored in a sample and hold circuit, with the indications of interval to interval increases and decreases in the integrated sensed values for a selected number, such as six, of the most recent time intervals stored in a shift register. For each time interval, a chaos detector counts the number of changes between increases and decreases for the selected number of most recent corresponding time intervals and accumulates a weighted sum of the counts which is time attenuated. When the sum reaches a predetermined amount, an output such as a trip signal for a circuit breaker is generated.
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Citations
16 Claims
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1. An arc fault detector for an ac electrical system, said arc fault detector comprising:
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input means generating from current flowing in said ac electrical system a sensed current signal from which at least a fundamental frequency component has been removed; integrating means repetitively integrating said sensed current signal over equal time intervals to generate integrated sensed current values; comparing means comparing said integrated sensed current value for the most recently completed time interval with said integrated sensed current value for the immediately previous corresponding time interval to generate indications of interval to interval increases and decreases in said integrated sensed current values; storing means storing said indication of interval to interval increases and decreases for a selected number of the most recently completed corresponding time intervals; and output means generating an arc fault signal as a function of a count of changes between said indications of interval to interval increases and decreases for said selected number of most recently completed corresponding time intervals stored by said storing means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A circuit breaker with arc fault protection comprising:
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a set of separable contacts; an operating mechanism operative to open said separable contacts in response to trip signals; and trip means comprising; overcurrent trip means responsive to current in an ac electrical system greater than a rated current to trip said operating mechanism; and arc fault trip means comprising; input means responsive to current in said ac electrical system including currents less than said rated current containing step changes such as occur when an arc is struck in said ac electrical system for generating a sensed current signal; integrating means repetitively integrating said sensed current signal over equal time intervals to generate integrated sensed current values; and means generating an arc fault trip signal to trip said operating mechanism as a function of the number of times said integrated value of said sensed current signal changes between an increase and a decrease in successive corresponding time intervals over a running set of a selected number of most recently completed corresponding time intervals. - View Dependent Claims (12, 13, 14, 15, 16)
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Specification