Self testing circuit breaker ground fault and sputtering arc trip unit

• US 5,459,630 A
• Filed: 09/15/1993
• Issued: 10/17/1995
• Est. Priority Date: 09/15/1993
• Status: Expired due to Term

• Current Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Wafer, John A., MacKenzie, Raymond W.
• Primary Examiner(s): DeBoer, Todd
• Application Number:
  US08/121,708
• Time in Patent Office: 762 Days
• Field of Search: 361/45, 361/47, 361/49, 361/86, 361/94, 361/113, 361/87, 324/510, 324/509, 324/514, 324/520, 324/522, 324/523, 324/527, 324/541, 324/544, 340/650, 340/651
• US Class Current: 361/45
• CPC Class Codes: G01R 31/3277 of low voltage devices, e.g. domestic or industrial devices, such as motor protections, relays, rotation switches
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 3/331 responsive to earthing of the neutral conductor H02H3/338 takes precedence
• 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

Ground fault trip units for circuit breakers are tested by a passive test circuit which includes a test conductor passing through the current transformer sensing coil(s), and a test switch which selectively connects the test conductor in a loop which simulates a neutral-to-ground fault. In a dormant oscillator ground fault test circuit, the test conductor loop passes through both sensing coils. When the neutral-to-ground detector is combined with a sputtering are fault detector sharing a common sensing coil, testing of all the components is accomplished by adding an additional test circuit which injects pulses derived from the line conductor into the sensing coil secondary, or which alternatively, connects a capacitor charged from a DC supply across the sensing coil secondary. Either of these alternative test circuits generates the successive events needed to produce a sputtering arc trip.

Claims

1. A ground fault trip unit for a circuit breaker protecting an electrical system having a line conductor and a grounded neutral conductor comprising:

sensing coil means through which said neutral conductor passes;

neutral-to-ground fault detection means connected to said sensing coil means and generating a trip signal for said circuit breaker in response to a neutral-to-ground fault in the protected electrical systems, test means coupled to said sensing coil means simulating a grounded neutral fault condition causing said neutral-to-ground fault detection means to generate said trip signal, said test means comprising a test conductor means extending through said sensing coil means, a test switch for selectively connecting said test conductor means in a closed loop which passes through said sensing coil means, said test conductor means having an impedance substantially equivalent to a maximum impedance of a neutral-to-ground fault in the protected electrical system.

2. The ground fault trip unit of claim 1 wherein said test conductor means comprises an electrical lead and a discrete impedance substantially equivalent to said impedance of said neutral-to-ground fault in the protected electrical system.

3. The ground fault trip unit of claim 1 wherein said test conductor means comprises an electrical conductor having a distributed impedance substantially equivalent to said impedance of said neutral-to-ground fault in the protected electrical system.

4. A trip unit for a circuit breaker in a protected electrical system having a line conductor and a neutral conductor and subject to sputtering arc faults and ground faults, said trip unit comprising:

sensing coil means sensing currents in said protected electrical system;

fault detector means connected to the sensing coil means for generating a trip signal in response to ground faults including grounded neutral faults and to sputtering arc faults; and

test means connected to said sensing coil means selectively injecting signals simulating grounded neutral and sputtering arc fault conditions into said fault detector means.

5. The trip unit of claim 4 wherein said test means comprises a test conductor extending through said sensing coil means, and a test switch for selectively connecting said test conductor in a closed loop extending through said sensing coil means.

6. The trip unit of claim 5 wherein said test conductor means has an impedance substantially equivalent to a maximum impedance of a grounded neutral fault in said protected electrical system.

7. The trip unit of claim 6 wherein said sensing coil means comprises a first sensing coil through which both said line conductor and said neutral conductor pass and a second sensing coil through which said neutral conductor but not said line conductor passes, wherein said fault detection means comprises a dormant oscillator ground fault detector circuit connected to said first and second sensing coils and a sputtering arc detector circuit connected to said second sensing coil, and wherein said test conductor means extends through both said first and second sensing coils.

8. The trip unit of claim 7 wherein said second coil has a secondary winding, wherein said sputtering arc detection circuit comprises means connected to said secondary winding generating a bandwidth limited di/dt signal where i is current in said neutral conductor, and means responsive to said di/dt signal to generate said trip signal under preselected conditions, and wherein said test means further comprises means injecting test signals into said secondary winding which cause said sputtering arc detector circuit to generate said trip signal.

9. A trip unit for a circuit breaker in a protected electrical system having a line conductor and a neutral conductor and subject to sputtering arc faults and ground faults, comprising:

sensing coil means sensing currents in said protected electrical system, fault detector means connected to the sensing coil means for generating a trip signal in response to ground faults including grounded neutral faults and to sputtering arc faults, test means connected to said sensing coil means selectively injecting signals simulating grounded neutral and sputtering arc fault conditions into said fault detector means, said test means comprising a test conductor extending through said sensing coil means, a test switch for selectively connecting said test conductor in a closed loop extending through said sensing coil means, said test conductor having an impedance substantially equivalent to a maximum impedance of a grounded neutral fault in said protected electrical system, said sensing coil means comprising a first sensing coil through which both said line conductor and said neutral conductor pass and a second sensing coil through which said neutral conductor but not said line conductor passes, wherein said fault detection means comprises a dormant oscillator ground fault detector circuit connected to said first and second sensing coils and a sputtering arc detector circuit connected to said second sensing coil, wherein said test conductor means extends through both said first and second sensing coils, said second coil having a secondary winding, wherein said sputtering arc detection circuit comprises means connected to said secondary winding generating a bandwidth limited di/dt signal where i is current in said neutral conductor, and means responsive to said di/dt signal to generate said trip signal under preselected conditions, wherein said test means further comprises means injecting test signals into said secondary winding which cause said sputtering arc detector circuit to generate said trip signal.

10. The trip unit of claim 9 wherein said means injecting test signals comprises an impedance means connected to said secondary winding and a switch selectively connecting said impedance means to said line conductor.

11. The trip unit of claim 9 wherein said means injecting test signals comprises a capacitor connected to said secondary winding, means charging said capacitor, and switch means selectively discharging said capacitor into said secondary winding.

12. The trip unit of claim 9 wherein said means responsive to said di/dt signal comprises level detector means comparing said di/dt signal to a threshold, and means responsive to said level detector generating a trip signal when said di/dt signal exceeds said threshold a predetermined number of times in a selected interval, and wherein said means injecting test signals into said secondary winding injects test signals in said secondary winding which exceed said threshold said predetermined number of times in said selected interval.

13. The trip unit of claim 12 wherein said means injecting test signals comprises impedance means connected to said secondary winding, and a switch selectively connecting said impedance means to said line conductor to inject AC pulses into said secondary winding.

14. The trip unit of claim 12 wherein said test means comprises a capacitor connected to said secondary winding, means charging said capacitor, and switch means selectively discharging said capacitor into said secondary winding to generate an oscillation.

15. A self testing trip unit for a circuit breaker in a protected electrical system having a line conductor and a neutral conductor and subject to sputtering arc faults, said trip unit comprising:

a sensing coil having one of said line and neutral conductors as a primary winding and having a secondary winding;

means connected to said secondary winding generating a bandwidth limited di/dt signal where i is current in said protected electrical system;

level detector means comparing said bandwidth limited di/dt signal to a selected threshold;

means generating a trip signal when said bandwidth limited di/dt signal exceeds said selected threshold a predetermined number of times in a selected interval; and

test means connected to said sensing coil for generating pulses which produce a bandwidth limited di/dt signal which exceeds said selected threshold said predetermined number of times within said selected interval.

16. The serf testing trip unit of claim 15 wherein said test means comprises impedance means connected to said secondary winding, and switch means selectively connecting said impedance means to said line conductor.

17. The serf testing trip unit of claim 15 wherein said test means comprises a capacitor connected to said secondary winding, means charging said capacitor, and switch means selectively discharging the capacitor into said secondary winding to produce an oscillation.

18. A trip unit for a circuit breaker in a protected ac electrical system having a line conductor and a neutral conductor, said trip unit comprising:

sensing means, sensing current in said protected electrical system, fault detection means connected to said sensing means and including means generating a trip signal in response to current patterns produced by sputtering arc faults in said protected electrical system, and test means coupled to said sensing means simulating said current patterns produced by sputtering arc faults to generate said trip signal.

19. The trip unit of claim 18 wherein said fault detector means comprises means responsive to a current pattern in which said current exceeds a preselected magnitude a predetermined number of times within a selected interval of time, and wherein said test means comprises means generating a test signal which exceeds said preselected magnitude said predetermined number of times within said selected interval of time.

20. The trip unit of claim 19 wherein said sensing means comprises sensing coil means through which said neutral conductor passes and said test means comprises test conductor means extending through said sensing coil means, and a test switch for selectively connecting said test conductor means in a closed loop which passes through said sensing coil means.

21. The trip unit of claim 19 wherein said sensing means comprises a lead connected to said neutral conductor and to a low pass filter followed by a high pass filter, and wherein said test means comprises an impedance and a switch which when selectively closed connects said impedance across the line conductor and neutral conductor, said impedance being connected to said low pass filter.

22. A trip unit for a circuit breaker in a protected ac electrical system having a line conductor and a neutral conductor, comprising:

sensing means, sensing current in said protected electrical system, fault detection means connected to said sensing means and including means generating a trip signal in response to current patterns produced by sputtering arc faults in said protected electrical system, test means coupled to said sensing means simulating said current patterns produced by sputtering arc faults to generate said trip signal, said fault detector means comprising means responsive to a current pattern in which said current exceeds a preselected magnitude a predetermined number of times within a selected interval of time, wherein said test means comprises means generating a test signal which exceeds said preselected magnitude said predetermined number of times within said selected interval of time, said sensing means comprising a lead connected to said neutral conductor and to a low pass filter followed by a high pass filter, wherein said test means comprises an impedance and a switch which when selectively closed connects said impedance across the line conductor and neutral conductor, said impedance being connected to said low pass filter.

23. The trip unit of claim 22 wherein said low pass filter comprises a resistor and capacitor, and said impedance and said resistor form a voltage divider which produces said test signal.