Arc fault detector immune to dimmer transients and a circuit breaker incorporating the same
AssigneeEaton Corporation
InventorsJoseph C. Zuercher, Steven Christopher Schmalz
Life of this patent
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Abstract
Tripping of a circuit breaker by an arc fault detector is blocked by a disable circuit upon detection of a transient associated with cold turn-on of an incandescent bulb powered by a dimmer. The peak value of pulses generated by the bandpass filter of the arc detector in response to step increases in the ac current is decayed approximately exponentially. The amplitude of each pulse is compared with upper and lower percentage limits of the decaying peak value. If the amplitudes of the pulses remain below the upper threshold for about 3 to 4 half cycles and exceed the lower threshold each half cycle, a dimmer transient is identified and logic is set to block generation of a false arc signal.
Claims15
Apparatus for detecting arc faults generating step changes in current each time an arc is struck in an ac electrical circuit having a dimmer generating in successive half cycles step changes in current which under certain transient conditions produce a dimmer transient current in which the step changes in current decay in amplitude in successive half cycles approximately exponentially from an initial transient value to a steady state value, the apparatus comprising:
- pulse generating means for generating a pulse signal having a pulse for each step change in current in the ac electrical circuit;
- response means responsive to repeated pulses generated by step changes in current above the steady state value for generating an arc signal;
- and
- disabling means responsive to the pulse signal for preventing the response means from generating the arc signal when the pulses in the pulse signal track the dimmer transient current within a predetermined margin.
An arc fault circuit breaker providing protection from arc faults generating step changes in current each time an arc is struck in an ac electrical circuit having the dimmer generating in successive half cycles step changes in current which under certain transient conditions produce a dimmer transient current in which the step changes in current decay in amplitude in successive half cycles approximately exponentially from an initial transient value to a steady state value, the circuit breaker comprising:
- separable contacts;
- an operating mechanism opening the separable contacts in response to a trip signal;
- and
- a trip unit generating a trip signal in response to selected current conditions in the electrical circuit, and including an arc fault detector generating a trip signal in response to an arc fault, the arc fault detector comprising:
- pulse generating means for generating a pulse signal having a pulse for each step change in current in the AC electrical circuit;
- response means responsive to repeated pulses generated by step changes in current above the steady state value for generating the trip signal;
- and
- disabling means responsive to the pulse signal for preventing the response means for generating the arc signal when the pulses in the pulse signal track the dimmer transient current within a predetermined margin.
Dependencies are inferred from the claim text.