Circuit interrupter including an electric arc monitoring circuit

• US 5,706,159 A
• Filed: 05/31/1995
• Issued: 01/06/1998
• Est. Priority Date: 03/30/1995
• Status: Expired due to Term

• Current Assignee: Siemens Industry Incorporated (Siemens AG)
• Original Assignee: Siemens Energy & Automation Incorporated (Siemens AG)
• Inventors: Strickland, Woothi, Dollar, Charles Randall II
• Primary Examiner(s): DeBoer, Todd
• Application Number:
  US08/455,771
• Time in Patent Office: 951 Days
• Field of Search: 361/113, 361/110, 361/85, 324/536
• US Class Current: 361/113
• CPC Class Codes: H02H 1/0015 Using arc detectors

Abstract

A circuit interrupter including an improved arc detection system which trips the interrupter in response to currents having frequencies and/or characteristics associated with arcing within the associated alternating current electrical system. The arc monitoring circuit determines if the signal produced by a current transducer is the result of arcing. The arc detection system includes two swept filters and associated amplifiers which produce a signal which has an amplitude representative of the frequencies present in the alternating current of the electric system. The portion of the filtered signal which has amplitudes above a predetermined level is integrated to produce a trip signal for the circuit interrupter when the value of the integration exceeds a predetermined limit.

Claims

1. An arc detector for producing an arc signal in response to an arc produced by the current in an electric conductor, the detector comprising:

a sensor coupled to the electrical conductor to produce a first signal representative of the current in the conductor, wherein the current has a plurality of frequencies;

a transform circuit coupled to the sensor to produce a second signal having amplitudes which represent the current at the plurality of frequencies; and

a monitoring circuit coupled to the transform circuit to monitor the amplitudes of the second signal corresponding to a range of the plurality of frequencies, and generating the arc signal when the amplitudes of the range correspond to an predetermined amplitude condition,

wherein the transform circuit comprises a first variable frequency filter which has a first center frequency which changes from a first frequency to a second frequency, the plurality of frequencies being between the first and second frequencies, and the first variable frequency filter being coupled to the sensor to produce the second signal having amplitudes which represent the current at the plurality of frequencies.

2. The arc detector of claim 1, wherein the sensor is a current transformer.

3. The arc detector of claim 1, wherein the sensor is a current shunt.

4. The arc detector of claim 1, wherein the monitoring circuit comprises:

an amplifying circuit coupled to the transform circuit to amplify the second signal to produce a third signal;

an integration circuit coupled to the amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal; and

a comparator circuit coupled to the integration circuit to output the arc signal when the integration signal exceeds the limit.

5. The arc detector of claim 1, wherein the center frequency of the first variable frequency filter cycles between the first and second frequencies at a constant rate over a first time period.

6. The arc detector of claim 5, wherein the first frequency is in the range of 2 to 8 megahertz and the second frequency is in the range of 12 to 18 megahertz.

7. The arc detector of claim 1, wherein the transform circuit comprises a second variable frequency filter which has a second center frequency which changes from the first frequency to the second frequency, the plurality of frequencies being between the first and second frequencies, and the second variable frequency filter being coupled to the first variable frequency filter to further filter the second signal.

8. The arc detector of claim 7, wherein the center frequency of the second variable frequency filter is offset from the center frequency of the first variable frequency filter.

9. The arc detector of claim 8, further comprising a first amplifying circuit coupled between the variable frequency filters.

10. The arc detector of claim 9, wherein the monitoring circuit comprises:

a second amplifying circuit coupled to the second variable frequency filter to amplify the second signal to produce a third signal;

an integration circuit coupled to the second amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal; and

a comparator circuit coupled to the integration circuit to output the arc signal when the integration signal exceeds the limit.

11. An arc detection circuit coupled to an electric conductor and generating an arc signal in response to a current within the conductor generated in response to an electric arc, the circuit comprising:

a transducer coupled to the electric conductor to generate a first signal representative of the current within the conductor;

a variable frequency filter circuit having a filter frequency which changes in response to a control signal, the filter being coupled to the output to generate a second signal having a plurality of amplitudes representative of the current at a respective plurality of frequencies; and

a threshold sensing circuit coupled to the variable frequency filter circuit to generate the arc signal when a plurality of the amplitudes representative of the currents at the respective plurality of frequencies within a range exceed at least one threshold amplitude.

12. The arc detector of claim 11, wherein the transducer is a current transformer.

13. The arc detector of claim 11, wherein the transducer is a current shunt.

14. The arc detector of claim 11, wherein the variable frequency filter circuit comprises first and second variable frequency filters which have a center frequency which changes from a first frequency to a second frequency, the plurality of frequencies being between the first and second frequencies, the first variable frequency filter being coupled to the sensor, and the second variable frequency filter is coupled to the first variable frequency filter to produce the second signal.

15. The arc detector of claim 14, wherein the center frequency cycles between the first and second frequencies at a constant rate over a first time period.

16. The arc detector of claim 15, wherein the first frequency is in the range of 2 to 8 megahertz and the second frequency is in the range of 12 to 18 megahertz.

17. The arc detector of claim 15, further comprising a first amplifying circuit coupled between the variable frequency filters.

18. The arc detector of claim 17, wherein the threshold sensing circuit comprises:

a second amplifying circuit coupled to the second variable frequency filter to amplify the second signal to produce a third signal;

an integration circuit coupled to the second amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal; and

a comparator circuit coupled to the integration circuit to output the arc signal when the integration signal exceeds the limit.

19. An arc detector comprising:

generating means for generating a first signal representative of an electric arc in an electrical conductor;

filtering means for filtering the first signal at a plurality of frequencies to generate a second signal;

monitoring means for monitoring the second signal to generate a third signal representative of the amplitude of the second signal within a range of the plurality of frequencies; and

detection means for generating an arc detection signal when the third signal is representative of arcing within the electrical conductor,

wherein the filtering means comprises a first variable frequency filter which has a first center frequency which changes from a first frequency to a second frequency, the plurality of frequencies being between the first and second frequencies, and the first variable frequency filter being coupled to the generating means to produce the second signal having amplitudes which represent the current at the plurality of frequencies.

20. The arc detector of claim 19, wherein the generating means is a current transformer.

21. The arc detector of claim 19, wherein the generating means is a current shunt.

22. The arc detector of claim 19, wherein the center frequency of the first variable frequency filter cycles between the first and second frequencies at a constant rate over a first time period.

23. The arc detector of claim 22, wherein the first frequency is in the range of 2 to 8 megahertz and the second frequency is in the range of 12 to 18 megahertz.

24. The arc detector of claim 22, wherein the monitoring means comprises:

an amplifying circuit coupled to the first variable frequency filter to amplify the second signal to produce the third signal; and

an integration circuit coupled to the amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal.

25. The arc detector of claim 24, wherein the detector means comprises a comparator circuit coupled to the integration circuit to output the arc detection signal when the integration signal exceeds the limit.

26. The arc detector of claim 19, wherein the filtering means further comprises a second variable frequency filter which has a second center frequency which changes from the first frequency to the second predetermined frequency, the plurality of frequencies being between the first and second frequencies, and the second variable frequency filter being coupled to the first variable frequency filter to further filter the second signal.

27. The arc detector of claim 26, wherein the center frequency of the second variable frequency filter is offset from the center frequency of the first variable frequency filter.

28. The arc detector of claim 27, further comprising a first amplifying circuit coupled between the variable frequency filters.

29. The arc detector of claim 28, wherein the monitoring means comprises:

a second amplifying circuit coupled to the second variable frequency filter to amplify the second signal to produce the third signal; and

an integration circuit coupled to the second amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal.

30. The arc detector of claim 29, wherein the detector means comprises a comparator circuit coupled to the integration circuit to output the arc detection signal when the integration signal exceeds the limit.

31. A circuit interrupter for interrupting the flow of current within at least one electrical conductor in response to arcing produced by current flow in the electrical conductor, the interrupter comprising:

a switching device coupled to the electrical conductor and operable to open the circuit defined by the electrical conductor in response to a trip signal;

a transducer coupled to the electrical conductor to generate a first signal representative of the electric current in the electrical conductor;

a variable frequency filter coupled to the transducer to generate a second signal representative of the first signal at a plurality of frequencies within a first range;

a monitoring circuit coupled to the variable frequency filter to generate a third signal representative of the power of a portion of the second signal, wherein the portion is generated from a second range of the plurality of frequencies in the first range; and

a trip circuit coupled to the switching device and the monitoring circuit to apply a trip signal to the switching device when the third signal is representative of an energy level of the portion of the second signal representative of arcing in the electrical conductor.

32. The circuit interrupter of claim 31, wherein the transducer is a current transformer.

33. The circuit interrupter of claim 31, wherein the transducer is a current shunt.

34. The circuit interrupter of claim 31, wherein the switching device is a circuit breaker including tripping coil coupled to the trip circuit.

35. The circuit interrupter of claim 34, wherein the variable frequency filter circuit comprises first and second variable frequency filters which have a center frequency which changes from a first frequency to a second frequency, the plurality of frequencies being between the first and second frequencies, the first variable frequency filter being coupled to the sensor, and the second variable frequency filter is coupled to the first variable frequency filter to produce the second signal.

36. The circuit interrupter of claim 35, wherein the center frequency cycles between the first and second frequencies at a constant rate over a first time period.

37. The circuit interrupter of claim 36, wherein the first frequency is in the range of 2 to 8 megahertz and the second frequency is in the range of 12 to 18 megahertz.

38. The circuit interrupter of claim 36, further comprising a first amplifying circuit coupled between the variable frequency filters.

39. The circuit interrupter of claim 38, wherein the trip circuit comprises:

a second amplifying circuit coupled to the second variable frequency filter to amplify the second signal to produce the third signal;

an integration circuit coupled to the second amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal; and

a comparator circuit coupled to the integration circuit to apply the trip signal to the tripping coil when the integration signal exceeds the limit.

40. A circuit interrupter comprising:

switching means for opening a circuit including an electrical conductor in response to a trip signal;

sensing means for generating a first signal representative of electric current in the electrical conductor;

filtering means for generating a second signal representative of the first signal filtered at a plurality of frequencies in a first range;

monitoring means for generating a third signal representative of the power of a portion of the second signal, wherein the portion is generated from a second range of the plurality of frequencies in the first range; and

trip means for applying a trip signal to the switching means when the third signal is representative of an energy level of the portion of the second signal representative of arcing in the electrical conductor,

wherein the filtering means comprises a first variable frequency filter which has a first center frequency which changes from a first frequency to a second frequency, the plurality of frequencies being between the first and second frequencies, and the first variable frequency filter being coupled to the generating means to produce the second signal having amplitudes which represent the current at the plurality of frequencies.

41. The circuit interrupter of claim 40, wherein the generating means is a current transformer.

42. The circuit interrupter of claim 40, wherein the generating means is a current shunt.

43. The circuit interrupter of claim 42, wherein the center frequency of the first variable frequency filter cycles between the first and second frequencies at a constant rate over a first time period.

44. The circuit interrupter of claim 43, wherein the first frequency is in the range of 2 to 8 megahertz and the second frequency is in the range of 12 to 18 megahertz.

45. The circuit interrupter of claim 44, wherein the monitoring means comprises:

an amplifying circuit coupled to the first variable frequency filter to amplify the second signal to produce the third signal; and

an integration circuit coupled to the amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal.

46. The circuit interrupter of claim 45, wherein the filtering means further comprises a second variable frequency filter which has a second center frequency which changes from the first frequency to the second frequency, the plurality of frequencies being between the first and second frequencies, and the second variable frequency filter being coupled to the first variable frequency filter to further filter the second signal.

47. The circuit interrupter of claim 46, further comprising a first amplifying circuit coupled between the variable frequency filters.

48. The circuit interrupter of claim 47, wherein the detector means comprises a comparator circuit coupled to the integration circuit to output the trip signal when the integration signal exceeds the limit.

49. The circuit interrupter of claim 44, wherein the trip means comprises a comparator circuit coupled to the integration circuit to output the trip signal when the integration signal exceeds the limit.

50. The circuit interrupter of claim 49, wherein the center frequency of the second variable frequency filter is offset from the center frequency of the first variable frequency filter.

51. The circuit interrupter of claim 50, wherein the monitoring means comprises:

a second amplifying circuit coupled to the second variable frequency filter to amplify the second signal to produce a third signal; and

an integration circuit coupled to the second amplifier to integrate the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal.

53. The method of claim 48, where in the step of filtering further includes the step of producing the second signal having amplitudes which represent the current at the plurality of frequencies.

54. The method of claim 53, wherein the step of monitoring further comprises the steps of:

amplifying the second signal to produce the third signal; and

integrating the third signal when the amplitude of the third signal exceeds a limit to produce an integration signal.

52. An electric arc detection method comprising the steps of:

generating a first signal representative of an electric current in an electrical conductor;

filtering the first signal at a plurality of frequencies to generate a second signal; and

monitoring the second signal to generate a third signal representative of the power of the second signal within a range of the plurality of frequencies,

wherein the step of filtering further comprises the step of cycling between the first and second frequencies at a constant rate over a first time period.

55. The method of claim 52, wherein the step of generating further comprises the step of outputting the arc detection signal when the integration signal exceeds the limit.