Circuit breaker responsive to repeated in-rush currents produced by a sputtering arc fault

• US 5,940,256 A
• Filed: 11/09/1994
• Issued: 08/17/1999
• Est. Priority Date: 02/26/1993
• Status: Expired due to Term

• Current Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: MacKenzie, Raymond W., Engel, Joseph C.
• Primary Examiner(s): Medley, Sally C.
• Application Number:
  US08/336,721
• Time in Patent Office: 1,742 Days
• Field of Search: 361/42, 361/43, 361/44, 361/93-95
• US Class Current: 361/42
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 1/043 to inrush currents H02H1/046 takes precedence; differential protection of transformers H02H7/045
• CPC Class Codes: H02H 3/335 the main function being self testing of the device
• CPC Class Codes: H02H 3/44 responsive to the rate of change of electrical quantities

Abstract

A circuit breaker responds to sputtering arc faults by counting the times that a bandwidth limited di/dt signal exceeds a threshold magnitude within a selected time interval. In the exemplary circuit breaker, if the threshold is exceeded twice within a one second interval, a trip solenoid is energized. The di/dt sensor can share a sensing coil with a ground fault detector. Alternatively, the resistance of the neutral lead within the circuit breaker is utilized to sense current which is converted to a bandwidth limited di/dt signal for level detection and counting of sputtering arc events.

Claims

1. A circuit breaker for protecting an ac electrical system from sputtering arc faults, comprising:

current sensing means sensing current flowing in said electrical system;

event signal generating means responsive to said current sensing means comprising means generating a bandwidth limited rate of change of current (di/dt) signal having a bandwidth selected to pass step increases in current, and means comparing said bandwidth limited di/dt signal to threshold values and generating an event signal when said threshold values are exceeded;

means generating a trip signal in response to a plurality of event signals within a preselected time interval; and

means responsive to said trip signal interrupting current flowing in said electrical system.

2. The circuit breaker of claim 1 wherein the means generating a trip signal generates the trip signal in response to two event signals within said preselected time interval.

3. The circuit breaker of claim 2 wherein the means generating a trip signal generates a trip signal in response to two event signals within about a one second time interval.

4. The circuit breaker of claim 1 wherein the means generating a trip signal comprises a counter counting said event signals.

5. The circuit breaker of claim 1 wherein said means generating a trip signal comprises a counter counting said event signals and timer means timing the selected interval.

6. The circuit breaker of claim 5 wherein said counter generates said trip signal when two event signals are generated within said predetermined time interval.

7. The circuit breaker of claim 6 wherein said timer means generates a timing interval of approximately one second.

8. The circuit breaker of claim 1 wherein said current sensing means comprises means generating a di/dt signal and said means generating said bandwidth limited di/dt signal comprises a two pole, low pass filter.

9. The circuit breaker of claim 1 wherein said current sensing means includes:

means connected across a selected portion of a conductor within said circuit breaker carrying current of said electrical system to utilize resistivity of said portion of said conductor to detect current, and means generating said bandwidth limited di/dt signal from the current detected.

10. The circuit breaker of claim 9 wherein said means generating said bandwidth limited di/dt signal comprises a low pass filter followed by a high pass filter.

11. The circuit breaker of claim 1 wherein said current sensing means comprises a current sensing transformer having one conductor of said electrical system as a primary winding and having a secondary winding in which a di/dt signal representative of a first derivative of current in said one conductor is induced, and wherein said means responsive to said current sensing means comprises means for bandwidth limiting said di/dt signal, and means generating said event signal a pulse each time the bandwidth limited di/dt signal exceeds said predetermined magnitude, and wherein said trip signal generating means comprises counter means generating a count of said pulses and generating said trip signal when said count reaches said plurality of event signals, and timer means setting said interval.

12. A circuit breaker for protecting an electrical system from ground faults and sputtering arc faults, comprising current sensing means sensing current flowing in said electrical system;

ground fault sensing means connected to said current sensing means and operative to generate a trip signal in response to a ground fault in said electrical system;

sputtering arc fault sensing means connected to said current sensing means to generate a trip signal in response to at least two successive step increases in current in said electrical system above a designated magnitude within a selected time interval; and

trip means responsive to trip signals generated by said ground fault sensing means and by said sputtering arc sensing means to interrupt current flowing in said electrical system.

13. The system of claim 12 wherein said electrical system includes a line conductor and a neutral conductor, wherein said current sensing means comprises a first current sensing transformer having said neutral conductor as a first primary winding and said line conductor as a second primary winding, and having a secondary winding, and a second current sensing transformer having said neutral conductor as a primary winding, having a secondary winding, and having a core generating in said secondary winding a signal representative of a rate of change of current in said neutral conductor, wherein said ground fault sensing means comprises a dormant oscillator ground fault detector connected to the secondary windings of said first and second current sensing transformers and generating said first trip signals, wherein said sputtering arc fault sensing means comprises a bandwidth limiting circuit connected to the secondary winding of said second current sensing transformer and generating a bandwidth limited rate of change of current signal, a level detector, connected to said bandwidth limiting circuit and generating an event signal when the bandwidth limited rate of change of current signal exceeds preset limits, and counter means counting events in which said bandwidth limited rate of change of current signal exceeds said preset limits within said selected time interval.