Arc fault circuit interrupter which detects the cessation of arcs of an arc fault

• US 6,999,289 B2
• Filed: 11/08/2002
• Issued: 02/14/2006
• Est. Priority Date: 11/09/2001
• Status: Active Grant

• Current Assignee: Pass & Seymour (Legrand SA)
• Original Assignee: Pass & Seymour Incorporated (Legrand SA)
• Inventors: Richards, Jeffrey C., Macbeth, Bruce F., Romano, James P.
• Primary Examiner(s): Sircus, Brian
• Assistant Examiner(s): KITOV, ZEEV V
• Application Number:
  US10/291,044
• Publication Number:
  US 20030099070A1
• Time in Patent Office: 1,194 Days
• Field of Search: 361/42, 361/5, 361/43, 361/44, 324/536, 324/546
• US Class Current: 361/5
• CPC Class Codes: H02H 1/0015 Using arc detectors

Abstract

An arc fault circuit interrupter which protects an AC circuit subjected to a possible arcing fault includes a sensor which produces a signal that can be evaluated to see if it is associated with arc fault current. The evaluation is done by a discrimination circuit which identifies a characteristic of the sensor signal associated with cessations of the arc fault current. An accumulator counts the number of occurrences of the cessations, and if the number of cessations counted within a predetermined time interval exceeds a predetermined number, the arc fault circuit interrupter interrupts the AC circuit.

Claims

1. An arc fault detector for protecting a circuit on an AC power line for distribution of an electrical current to a circuit, comprising:

at least one sensor coupled to the AC power line, the sensor being configured to provide a sensor output signal;

a detection circuit coupled to the at least one sensor, the detection circuit being configured to detect a current step transition from the sensor output signal;

a processing circuit configured to determine whether the current step transition represents an arc cessation event, and provide a discriminator output pulse when the current step transition represents an arc cessation event, whereby arc initiation events are ignored by the discriminator; and

an accumulator configured to increment a count for each discriminator output pulse received during a first predetermined time interval, the accumulator providing a detection signal if the counter value exceeds a first predetermined number.

2. The device according to claim 1, further comprising an interrupting mechanism responsive to said accumulator, said interrupting mechanism being configured to interrupt said electrical current to said circuit in response to the detection signal.

3. The device according to claim 1, wherein said AC power line consists of a plurality of conductors, and wherein said sensor is coupled to at least one of said plurality of conductors.

4. The device according to claim 3, wherein said sensor consists of a shunt resistor.

5. The device according to claim 1, wherein the processing circuit is configured to identify a predetermined pattern of said step transitions exceeding said first predetermined number of said step transitions within said first predetermined time interval.

6. The device according to claim 1, wherein said detection circuit comprises:

a zero cross detector for detecting the given polarity of at least one of a power line voltage or said electrical current; and

a current step directional detector for identifying if said step transition in said electrical current is a step increase or a step decrease;

wherein said processing circuit determines which current step transitions are to be counted by said accumulator depending on a polarity of said power line voltage at a time of said step transition increase or step transition decrease in said electrical current.

7. The device according to claim 6, further comprising a gate that prevents step transition changes in said electrical current from being counted by said accumulator that occur within designated portions of half cycles of said power line voltage.

8. The device according to claim 7, wherein said gate prevents step transition changes in said electrical current occurring at current or voltage zero crossings identified by said zero cross detector from being counted by said accumulator.

9. The device according to claim 7, wherein said gate prevents step transition changes in said electrical current during a first 5 milliseconds of each half cycle of said power line voltage or said electrical current from being counted by said accumulator.

10. The device according to claim 1, further comprising:

differentiation means for differentiating said output from said sensor to produce di/dt signals in response to step transition increases or step transition decreases in said electrical current and wherein said di/dt signals have polarity; and

a polarity detector for detecting a polarity of at least one of power line voltage and said electrical current;

wherein said processing circuit receives a signal from said differentiation means and a zero cross detector and allows only di/dt pulses, indicative of electrical current step transitions, to be counted by said accumulator that are of a proper polarity in relationship to said polarity of at least one of said power line voltage and said electrical current.

11. The device according to claim 10, wherein said first predetermined time interval is initiated by a di/dt pulse of proper polarity with respect to one of said power line voltage and said electrical current polarity.

12. The device according to claim 10, further comprising a gate that prevents step transition changes in said di/dt pulses from being counted by said accumulator that occur within specified portions of each half cycle of said power line voltage.

13. The device according to claim 12, wherein said gate prevents di/dt pulses in said electrical current occurring at current or voltage zero crossings identified by said zero cross detector from being counted by said accumulator.

14. The device according to claim 12, wherein said gate prevents said di/dt pulses occurring during a first 5 milliseconds of each half cycle of said power line voltage or said electrical current from being counted by said accumulator.

15. The device according to claim 10, furthermore comprising a second differentiator for differentiating an output from said differentiation means to produce differentiated di/dt signals in response to step transition increases and step transition decreases in said electrical current and wherein said differentiated di/dt signals have an associative leading edge polarity in response to said step transition increases and decreases in said electrical current;

wherein said processing circuit receives an output from said second differentiator and said output from said polarity detector, and wherein said accumulator counts only those differentiated di/dt pulses whose leading edges are of proper polarity in relationship to said output from said polarity detector.

16. The device according to claim 1 wherein said first predetermined time interval is initiated by an arc-indicative event.

17. The device according to claim 16, further comprising:

a voltage monitor for monitoring a voltage from said AC power line;

means for determining randomness in at least one of said output from said sensor and said voltage monitored by said voltage monitor;

wherein said arc-indicative event is discerned from said randomness from at least one of said sensor and said voltage monitor; and

wherein said means for determining randomness includes using one of pulse width modulation (PWM), pulse position modulation (PPM), and pulse amplitude modulation (PAM) techniques.

18. The device according to claim 16 wherein said arc-indicative event is a step transition increase or a step transition decrease in said electrical current.

19. The device according to claim 1, further comprising:

a current sensor for sensing an amount of said electrical current; and

a threshold detector for determining if said output from said current sensor exceeds a predetermined threshold;

wherein said accumulator is responsive to said first predetermined number when said output is less than said predetermined threshold, and responsive to a second predetermined number when said output exceeds said predetermined threshold.

20. The device according to claim 19, wherein said first predetermined number is greater than said second predetermined number.

21. The device according to claim 1, further comprising:

a current sensor for sensing an amount of said electrical current;

a threshold detector for determining if said output from said current sensor exceeds a predetermined threshold;

wherein said first predetermined time interval is initiated by a first event if said output is less than said predetermined threshold, and initiated by a second event if said output exceeds said predetermined threshold.

22. The device according to claim 21, further comprising:

a voltage monitor for monitoring a voltage from said AC power line;

means for determining randomness in at least one of said output from said sensor and said voltage monitored by said voltage monitor;

wherein an arc-indicative event is discerned from said randomness from at least one of said sensor and said voltage monitor; and

wherein said means for determining randomness includes using one of pulse width modulation (PWM), pulse position modulation (PPM), and pulse amplitude modulation (PAM) techniques.

23. The device according to claim 21, wherein said second event includes an arc-indicative event consisting of a predetermined initiation pattern of said step transitions counted by said accumulator.

24. The device according to claim 21, wherein said first event includes an arc-indicative event indicated by a first initiation count of said step transitions counted by said accumulator, wherein said second event includes an arc-indicative event indicated by a second initiation count of said step transitions counted by said accumulator, and wherein said first initiation count exceeds said second initiation count.

25. The device according to claim 1, wherein said first predetermined time interval includes a plurality of half line cycles of voltage or current associated with said AC power line, wherein said step transitions fail to occur for a second predetermined time interval within said first predetermined time interval, and wherein said accumulator is responsive to said count exceeding a predetermined number only if said second predetermined interval is detected by said accumulator.

26. The device according to claim 1, wherein said first predetermined time interval is initiated by an arc-indicative event comprising momentary absence of sensed step transitions for a second predetermined interval.

27. The device according to claim 1, wherein said AC power line is connected to an inductive load, said device further comprising:

a phase shift detector that measures a phase shift related to said inductive load; and

a gate that prevents step transition changes in said electrical current from being counted by said accumulator that occur within specified portions of half cycles of said power line; and

wherein an output from said phase shift detector determines a position of said portions with respect to positions of zero crossings in said half cycles of said power line.

28. The device according to claim 27, further comprising:

a current zero cross detector for sensing current zero crossings in said electrical current through said inductive load; and

a voltage zero cross detector for sensing voltage zero crossings in voltage on said AC power line;

wherein said phase shift detector determines said phase shift from output signals from said current and voltage zero cross detectors.

29. The device according to claim 1, wherein said sensor comprises a shunt, said device further comprising:

a first differentiator for differentiating said output from said sensor to produce di/dt signals in response to step transition increases and step transition decreases in said electrical current, wherein said di/dt signals have an associative polarity in response to said step transition increases and decreases said in electrical current; and

a polarity detector for detecting a polarity of said AC power line voltage or said electrical current;

wherein said processing circuit receives an output from said first differentiator and an output from said polarity detector, and wherein said accumulator counts only those di/dt signals that are of proper polarity in relationship to said output from said polarity detector.

30. The device according to claim 1, wherein said detection circuit and/or processing circuit includes a half wave gate for blocking said current step transitions from being counted by said accumulator that occur in a predetermined polarity of said power line voltage or said electrical current.

31. The device according to claim 30, wherein said half wave gate comprises a half wave power supply.

32. The device according to claim 30, wherein said detection circuit and/or processing circuit blocks said step transition signals of improper polarity from being counted by said accumulator.

33. The device according to claim 1, further comprising:

means for producing a signal proportional to a magnitude of said step transitions in said current; and

a threshold detector for producing said sensed step transitions when said signal exceeds a predetermined amplitude.

34. An arc fault detector, comprising:

detection means for detecting an arc fault rate of current change in an electrical current delivered from an AC power source, wherein a polarity of said arc fault rate of current change is opposite to a polarity of said electrical current containing said arc fault rate of current change;

gate means for permitting acceptance of said arc fault rate of current change during one or more predetermined intervals of one or more cycles of said AC power source into an accumulator;

determining means for determining when an accumulator of said accepted arc fault rate of current in said accumulator matches a predetermined pattern, during a predetermined time interval;

signaling means, responsive to said determining means, for signaling a circuit interrupter to interrupt said electrical current.

35. An arc fault circuit detector used in conjunction with an arc fault circuit interrupter for protecting an AC circuit subjected to a possible arcing fault, comprising:

a sensor for producing a signal associated with the arc fault current;

a discrimination circuit for identifying a characteristic of said sensor signal associated with cessations of said arc fault current; and

an accumulator for counting a number of occurrences of said cessations;

in which when said number of cessations exceeds a first predetermined number during a first predetermined time interval, an output signal indicative of an arc fault is produced.

36. The device as in claim 35, wherein said output signal causes said arc fault circuit interrupter to interrupt said AC circuit.

37. The device as in claim 35, further comprising a circuit for detecting high current cessations associated with high arcing fault currents, wherein if said high current cessations exceed a second predetermined number over a second predetermined interval, said arc fault circuit interrupter is caused to interrupt said circuit in a sped up mode.

38. An arc fault detector for detecting arc faults which have an associated electrical current in an AC power line, comprising:

means for sensing said electrical current; and

means for detecting a current step transition from the means for sensing;

means for determining whether the current step transition is an arc cessation event or an arc initiation event, the means for determining being configured to ignore arc initiation events; and

means for counting arc cessation events during a predetermined time period and providing a detection signal when the number of counted arc cessation events exceeds a predetermined amount.

39. A method for detecting arc faults that have an associated electrical current in an AC power line, comprising the steps of:

sensing said electrical current; and

detecting a current step transition from the sensed electrical current;

determining whether the current stern transition is an arc cessation event or an arc initiation event, the means for determining ignoring arc initiation events; and

counting arc cessation events during a predetermined time period and providing a detection signal when the number of counted arc cessation events exceeds a predetermined amount.