Arc fault circuit interrupter recognizing arc noise burst patterns

• US 6,839,208 B2
• Filed: 02/16/2001
• Issued: 01/04/2005
• Est. Priority Date: 02/17/2000
• Status: Expired due to Term

• Current Assignee: Pass & Seymour Incorporated (Legrand SA)
• Original Assignee: Pass & Seymour Incorporated (Legrand SA)
• Inventors: Richards, Jeffrey C., Packard, Thomas N., Macbeth, Bruce F., Romano, James P.
• Primary Examiner(s): HUYNH, KIM NGOC
• Application Number:
  US09/788,206
• Publication Number:
  US 20010033469A1
• Time in Patent Office: 1,418 Days
• Field of Search: 361/42, 361/45, 361/94, 361/90, 361/93.1, 324/520, 324/528, 324/522, 324/76.11, 324/535, 324/536, 702/57, 702/58, 702/64, 702/65, 702/75, 702/79
• US Class Current: 361/42
• CPC Class Codes: G01R 31/14 Circuits therefor , e.g. for generating test voltages, sensing circuits G01R31/1209 - G01R31/1227 take precedence; for testing switches G01R31/327
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 3/44 responsive to the rate of change of electrical quantities

Abstract

An arc fault circuit interrupter (AFCI) detects arc faults by identifying the various signature patterns of arc fault noise while rejecting arc mimicking noise from normal load phenomena.

Claims

1. An arc fault detector for protecting electric power lines, comprising:

a sensor coupled to said power lines for detecting broad band arc noise;

a di/dt detector connected to said sensor for generating an output pulse having a time width associated with a time during which a pulse of broad band arc noise is above a predetermined threshold;

a processor connected to said detector;

a power line zero cross detector generating a time reference pulse for said processor;

wherein said processor evaluates a width of said di/dt detector output pulse during each half wave following a zero cross pulse and opens a detection window for a first predetermined number of power line half cycles if, during any one power line half cycle, either (a) said width of said output pulse is equal to or exceeds a first predetermined interval, or (b) said width of said output pulse is equal to or exceeds two or more second predetermined intervals;

wherein a length of said second predetermined interval is less than a length of said first predetermined interval; and

wherein during said open detection window said processor ignores said output pulses for a rejection period lasting a second predetermined number of half cycles at a start of said window.

2. An arc fault detector according to claim 1, further comprising means for discriminating between arc fault signals and arc mimicking signals that occur after said rejection period but during said open detection window.

3. An arc fault detector according to claim 2, wherein said means for discriminating includes at least one firewall selected from the group consisting of MINIMUM CURRENT REJECT, PHASE ANGLE REJECT, QUIET INTERVAL DETECT, and CONTINUOUS NOISE REJECT.

4. An arc fault detector according to claim 1, wherein said detection window is opened only if a load current is equal to or exceeds 5 amperes.

5. An arc fault detector according to claim 1, further comprising a selector switch which acts to select a sensitivity of said detector to a magnitude of arc faults.

6. An arc fault detector according to claim 1, wherein said detection window is opened only if said half wave is not substantially filled with arc noise.

7. An arc fault detector according to claim 1, wherein said processor ignores all half waves which are substantially filled with arc noise.

8. An arc fault detector according to claim 1, further comprising:

a low pass filter connected to said sensor having a break frequency equivalent to a fundamental frequency of said power lines;

a level detector connected to said low pass filter, in which activation of said level detector at a predetermined magnitude of a frequency of a line current in said power lines causes said processor to evaluate said di/dt detector output pulse during each half wave following a zero cross pulse and to open a detection window for a first predetermined number of power line half cycles if during any one power line half cycle the width of the output pulse is equal to or exceeds a third predetermined interval, and during which open detection window said processor ignores said output pulses for a rejection period lasting said second predetermined number of half cycles at said start of the window; and

wherein said processor produces an arc detection signal if, at any time after said rejection period, said detector output pulse width exceeds a fourth predetermined interval, said fourth predetermined interval being greater than said third predetermined interval.

9. An arc fault detector according to claim 1, further comprising interrupting means for interrupting current through said power lines downstream of said sensor, wherein said interrupting means includes:

an SCR as a trip switch; and

a Zener diode directly coupling said sensor output to a gate of said SCR, wherein a breakover voltage of said Zener diode is selected at a predetermined level such that said sensor output directly triggers said SCR during large fault currents.

10. An arc fault detector according to claim 1, further comprising:

a high current override, wherein said sensor is coupled to an amplifier through a high pass filter which rejects a signal from said sensor due to the frequency of a line current in said power lines; and

said high current override including a bypass element which allows said signal to bypass said high pass filter, wherein a predetermined level of a load current results in said detector generating a pulse which is detected by said processor as an arc fault.

11. A method for detecting and interrupting arc faults in electric power lines, comprising the steps of:

sensing random high frequency components in a load current of said electric power lines;

producing pulse signals whose widths correspond to durations of said high frequency components;

opening a window upon detection of a first pattern of said pulse signals;

ignoring said pulse signals after said window is opened for a first predetermined interval; and

interrupting load power in said electric power lines when one of said first pattern of pulse signals and a second pattern of pulse signals occurs after said step of ignoring while said window remains open.

12. A method according to claim 11, further comprising the step of determining a phase angle of each trailing portion initiation of an arc fault using a zero cross detector.

13. A method according to claim 11, further comprising the step of determining patterns of pulse signals with respect to half cycles of the power line frequency.

14. A method according to claim 13, further comprising the step of using a zero cross detector to determine the position of said half cycles.

15. A method according to claim 11, further comprising the step of ignoring said pulse signals while said window is open if there is a presence of pulse signals for a second predetermined interval.

16. A method according to claim 15, wherein said second predetermined interval is a half cycle of the power line frequency.

17. A method according to claim 11, further comprising the step of preventing tripping of a circuit interrupter if said pulse signals continue without interruption for a second predetermined interval.

18. A method according to claim 17, wherein said second predetermined interval is one half cycle of the power line frequency.

19. A method according to claim 11, further comprising the step of producing a trip signal if a line frequency component is above a threshold irrespective of said high frequency components.

20. A method according to claim 19, wherein said threshold is 500 amperes.

21. A method according to claim 11, further comprising the step of amplifying said high frequency component using a voltage doubler circuit, said step of amplifying occurring after the step of sensing and before the step of producing.

46. A method according to claim 11, further comprising the step of disabling detection of said pulse signals if a magnitude of said line frequency component is below a threshold current.

47. A method according to claim 46, wherein said threshold current is 5 amperes.

22. A method for detecting and interrupting arc faults in electric power lines,comprising the steps of:

sensing line frequency components and random high frequency components in a load current of said electric power lines;

producing pulse signals whose widths correspond to durations of said high frequency components;

opening a window upon detection of at least one predetermined first pattern of pulse signals;

comparing a magnitude of a power line frequency against a threshold;

tripping a circuit interrupter on said electric power lines if a second pattern of pulse signals occurs when said window is open and said power line frequency is below said threshold; and

tripping said circuit interrupter if a third pattern of pulse signals occur when said window is open and said power line frequency is above said threshold.

23. A method according to claim 22, further comprising the step of disabling detection of said pulse signals if a magnitude of said line frequency component is below a threshold current.

24. A method according to claim 23, wherein said threshold current is 5 amperes.

25. A method according to claim 22, further comprising the step of ignoring said pulse signals while said window is open if there is a presence of pulse signals for a predetermined interval.

26. A method according to claim 25, wherein said predetermined interval is a half cycle of the power line frequency.

27. A method according to claim 22, further comprising the step of preventing tripping of a circuit interrupter if said pulse signals continue without interruption for a predetermined interval.

28. A method according to claim 27, wherein said interval is one half cycle of the power line frequency.

29. A method according to claim 22, further comprising the step of producing a trip signal if one of said line frequency components is above a threshold irrespective of said high frequency components.

30. A method according to claim 29, wherein said threshold is 500 amperes.

31. A method according to claim 22, further comprising the step of amplifying said high frequency component using a voltage doubler circuit, said step of amplifying occurring after the step of sensing and before the step of producing.

32. An apparatus for detecting and interrupting arc faults in electric power lines, comprising:

means for sensing random high frequency components in a load current of said electric power lines;

means for producing pulse signals whose widths correspond to durations of said high frequency components;

means for opening a window upon detection of a first pattern of said pulse signals;

means for ignoring said pulse signals after said window is opened for a first predetermined interval; and

means for interrupting load power in said electric power lines when one of said first pattern of pulse signals and a second pattern of pulse signals occurs after said step of ignoring while said window remains open.

33. An apparatus according to claim 32, further comprising means for determining a phase angle of each trailing portion initiation of an arc fault using a zero cross detector.

34. An apparatus according to claim 32, further comprising means for determining patterns of pulse signals with respect to half cycles of the power line frequency.

35. An apparatus according to claim 34,further comprising means for using a zero cross detector to determine the position of said half cycles.

36. An apparatus according to claim 32, further comprising means for disabling detection of said pulse signals if a magnitude of said line frequency component is below a threshold current.

37. An apparatus according to claim 36, wherein said threshold current is 5 amperes.

38. An apparatus according to claim 32, further comprising means for ignoring said pulse signals while said window is open if there is a presence of pulse signals for a second predetermined interval.

39. An apparatus according to claim 38, wherein said second predetermined interval is a half cycle of the power line frequency.

40. An apparatus according to claim 32, further comprising means for preventing tripping of a circuit interrupter if said pulse signals continue without interruption for a second predetermined interval.

41. An apparatus according to claim 40, wherein said second predetermined interval is one half cycle of the power line frequency.

42. An apparatus according to claim 32, further comprising means for producing a trip signal if one of said line frequency components is above a threshold irrespective of said high frequency components.

43. An apparatus according to claim 42, wherein said threshold is 500 amperes.

44. An apparatus according to claim 32, further comprising means for amplifying said sensed high frequency component using a voltage doubler circuit before said pulse signals are produced.

45. An apparatus for detecting and interrupting arc faults in electric power lines, comprising:

means for sensing line frequency components and random high frequency components in a load current of said electric power lines;

means for producing pulse signals whose widths correspond to durations of said high frequency components;

means for opening a window upon detection of at least one predetermined first pattern of pulse signals;

means for comparing a magnitude of a power line frequency against a threshold;

means for tripping a circuit interrupter on said electric power lines if a second pattern of pulse signals occurs when said window is open and said power line frequency is below said threshold; and

means for tripping said circuit interrupter if a third pattern of pulse signals occur when said window is open and said power line frequency is above said threshold.

48. An apparatus according to claim 45, further comprising means for disabling detection of said pulse signals if a magnitude of said line frequency component is below a threshold current.

49. An apparatus according to claim 48, wherein said threshold current is 5 amperes.

50. An apparatus according to claim 45, further comprising means for ignoring said pulse signals while said window is open if there is a presence of pulse signals for a predetermined interval.

51. An apparatus according to claim 50, wherein said predetermined interval is a half cycle of the power line frequency.

52. An apparatus according to claim 45, further comprising means for preventing tripping of a circuit interrupter if said pulse signals continue without interruption for a predetermined interval.

53. An apparatus according to claim 52, wherein said predetermined interval is one half cycle of the power line frequency.

54. An apparatus according to claim 45, further comprising means for producing a trip signal if one of said line frequency components is above a threshold irrespective of said high frequency components.

55. An apparatus according to claim 54, wherein said threshold is 500 amperes.

56. An apparatus according to claim 45, further comprising means for amplifying said sensed high frequency component using a voltage doubler circuit before said pulse signals are produced.