Arc fault detector with immunity to tungsten bulb burnout and circuit breaker incorporating same

• US 5,805,398 A
• Filed: 09/29/1997
• Issued: 09/08/1998
• Est. Priority Date: 09/29/1997
• Status: Expired due to Term

• Current Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Rae, Thomas Christopher
• Primary Examiner(s): Gaffin, Jeffrey A.
• Assistant Examiner(s): Sherry, Michael J.
• Application Number:
  US08/939,976
• Time in Patent Office: 344 Days
• Field of Search: 361/42, 361/49-50, 361/79, 361/86-87, 361/93-94, 361/102, 361/111, 361/45, 335/201, 324/76.41, 324/76.44, 324/76.45, 324/520, 324/522, 364/483, 364/484, 364/486
• US Class Current: 361/42
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 1/04 Arrangements for preventing response to transient abnormal conditions, e.g. to lightning or to short duration over voltage or oscillations; Damping the influence of dc component by short circuits in ac networks

Abstract

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.

Claims

1. A circuit breaker for interrupting current in an electrical system subject to arc faults generating step increases in current each time an arc is struck and subject to other current pulses of at least a certain high amplitude, said circuit breaker comprising:

separable contacts which interrupt said current in said electrical system when open; and

trip means comprising pulse generating means generating a pulse a signal containing pulses related in amplitude to said step increases in current each time an arc is struck and containing pulses related in amplitude to said other current pulses, zener diode means limiting amplitude of said pulses in said pulse signal to a selected amplitude which is less than said certain high amplitude of said other current pulses to produce conditioned pulses, means generating a trip signal as a function of a time attenuated accumulation of said conditioned pulses, and means responsive to said trip signal to open said separable contacts.

2. The circuit breaker of claim 1 wherein said pulse generating means includes means generating said pulse signal with pulses of a single polarity, said zener diode means comprises a single zener diode polarized to limit said amplitude of said pulses of said single polarity, and said means generating said trip signal comprises a capacitor, means applying said conditioned pulses to said capacitor to apply charge to said capacitor, adjusting means connected to said capacitor for adjusting charge on said capacitor at a selected rate in an opposite sense from said charge applied by said conditioned pulses, and output means generating said trip signal when voltage on said capacitor reaches a predetermined value, said capacitor and adjusting means being selected such that said voltage on said capacitor represents said time attenuated accumulation.

3. A circuit breaker for interrupting current in an electrical system subject to arc faults generating step increases in current each time an arc is struck and subject to current pulses generated by a tungsten bulb in said electrical system, said circuit breaker comprising:

separable contacts which interrupt said current in said electrical system when open; and

trip means comprising pulse generating means generating a pulse signal containing pulses of a single polarity related in amplitude to said step increases in current each time an arc is struck and containing pulses of said same single polarity related in amplitude to current pulses generated by said tungsten bulb, a zener diode limiting amplitude of said pulses in said pulse signal to a selected amplitude which is less than the amplitude of said pulses related in amplitude to said pulses generated by said tungsten bulb to produce conditioned pulses, and means generating a trip signal comprising a capacitor, means applying said conditioned pulses to said capacitor to apply charge to said capacitor, adjusting means connected to said capacitor for adjusting charge on said capacitor at a selected rate in an opposite sense from said charge applied by said conditioned pulses, and output means generating said trip signal when voltage on said capacitor reaches a predetermined value, said capacitor and adjusting means being selected such that said voltage on said capacitor represents said time attenuated accumulation; and

means opening said separable contacts in response to said trip signal.

4. The circuit breaker of claim 3 wherein said trip means further includes ground fault trip means responsive to ground faults in said electrical system, and wherein said means opening said separable contacts is also responsive to said ground fault trip signal.

5. Apparatus for detecting arc faults generating step increases in current each time an arc is struck in an electrical system which is also subject to other current pulses of at least a certain high amplitude, said apparatus comprising:

pulse generating means generating a pulse signal containing pulses related in amplitude to said step increases in current each time an arc is struck and containing pulses related in amplitude to said other current pulses, zener diode means limiting amplitude of said pulses in said pulse signal to a selected amplitude which is less than the amplitude of said pulses related in amplitude to said other current pulses to produce conditioned pulses, and means generating an arc fault signal as a function of a time attenuated accumulation of said conditioned pulses.

6. The apparatus of claim 5 wherein said pulse generating means includes means generating said pulse signal with pulses of a single polarity, said zener diode means comprises a single zener diode polarized to limit said amplitude of said pulses of said single polarity, and said means generating said arc fault signal comprises a capacitor, means applying said conditioned pulses to said capacitor to apply charge to said capacitor, adjusting means connected to said capacitor for adjusting charge on said capacitor at a selected rate in an opposite sense from said charge applied by said conditioned pulses, and output means generating said arc fault signal when voltage on said capacitor reaches a predetermined value, said capacitor and adjusting means being selected such that said voltage on said capacitor represents said time attenuated accumulation.

7. The apparatus of claim 6 wherein said adjusting means comprises a resistor connected in parallel with said capacitor.