Arc fault detector with circuit interrupter and early arc fault detection

• US 6,407,893 B1
• Filed: 10/02/2000
• Issued: 06/18/2002
• Est. Priority Date: 12/19/1997
• Status: Expired due to Term

• Current Assignee: Leviton Manufacturing Company Incorporated
• Original Assignee: Leviton Manufacturing Company Incorporated
• Inventors: Bradley, Roger M., Rose, William J., Pearse, James N., Neiger, Benjamin B.
• Primary Examiner(s): Leja, Ronald W.
• Application Number:
  US09/677,801
• Time in Patent Office: 624 Days
• Field of Search: 361/42-50, 361/63, 361/78, 361/79, 361/88, 361/91.1, 361/93.1, 361/99.111, 361/93.2, 361/93.5, 361/93.6, 324/508, 324/509, 324/512, 324/520, 324/525, 702/58, 702/134, 702/FOR.103, 702/FOR.104, 702/FOR.105, 702/FOR.107
• US Class Current: 361/42
• CPC Class Codes: G01R 31/12 Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing G01R31/08, G01R31/327 and G01R31/72 take precedence; measuring in plasmas G01R19/0061; measuring dielectric constants G01R27/2617; ESD, EMC or EMP testing of circuits G01R31/002
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 1/0038 concerning the connection of the detecting means, e.g. for reducing their number
• CPC Class Codes: H02H 3/334 with means to produce an artificial unbalance for other protection or monitoring reasons or remote control H02H3/338 takes precedence

Abstract

An arc fault detector comprised as a stand alone unit and in combination with a ground fault circuit interrupter (GFCI) functions to provide protection from potentially dangerous arc fault conditions. When combined with a GFCI, the combination arc fault/ground fault circuit interrupter (AFCI/GFCI) provides protection from both arc fault and ground fault conditions. A single transformer is used to detect faults between neutral and ground and arc faults. An impedance splits the current flow into two portions so as to generate differential current proportional to the current flowing through the conductors. An early arcing detector periodically tests the AC line for high impedance between the device and a main breaker panel. The AFCI/GFCI device detects both AC line frequencies and high frequencies associated with arcing. Both average and instantaneous values of both AC line frequency and high frequency arcing signals are processed to generate an arc fault signal. The device allows the arc detector to differentiate between destructive high level arcing and low level arcing such as generated by typical household appliances and equipment. This serves to decrease the occurrence of false tripping. The device also includes a timer circuit, which permits the user to temporarily disable the arc detector, and includes communication means to permit the device to communicate the occurrence and location of the arc fault to a centralized monitoring station.

Claims

1. An arc fault detector capable of being electrically connected to an electrical wiring system having a source of electric power comprising:

indicating means for providing an indicia representing the presence of at least one arc fault condition in the electrical wiring system;

trigger means, responsive to a trigger signal received after activation of the trigger means, for causing said indicating means to provide the indicia;

means for activating said trigger means for a predetermined period of time when a voltage of the source of electrical power is below a predetermined value; and

first arc fault detecting means for detecting a line impedance associated with the electrical wiring system after said activating means activates said trigger means, and for generating a line impedance signal when said detected line impedance is greater than a predetermined value with the line impedance signal being output as the trigger signal to the trigger means.

2. The device according to claim 1, wherein said line impedance trigger signal activates said trigger means.

3. The device according to claim 1, wherein said first arc fault detecting means comprises:

a transformer through which phase and neutral conductors pass and a current splitter connected to the electrical wiring system such that a line impedance arc fault sense signal proportional to the current flowing through the electrical wiring system is generated by said transformer.

4. The device according to claim 3, wherein said current splitter comprises an impedance connected in parallel with said transformer.

5. The device according to claim 3, wherein said current splitter comprises a resistance connected in parallel with said transformer.

6. The device according to claim 3, wherein said current splitter comprises a reactance connected in parallel with said transformer.

7. The device according to claim 1, wherein said activating means activates said trigger means at a predefined interval.

8. The device according to claim 7, wherein said predefined interval is every half cycle of said source of electrical power.

9. The device according to claim 1, wherein said first arc fault detecting means generates as said line impedance trigger signal a pulse substantially proportional to the impedance of said electrical wiring system.

10. The device according to claim 1, wherein when activated said activating means loads an LC network across the source of electrical power, such that a pulse generated therefrom is indicative of a high impedance condition.

11. The device according to claim 1 further comprising a second arc fault detecting means for sensing a level of AC current flowing through an electrical load placed on said electrical wiring system, for generating peak and average high frequency signals, for generating peak and average AC line frequency signals, and for generating a signal level trigger signal in response to at least one of said peak high frequency signal, said average high frequency signal, said peak AC line frequency signal and said average AC line frequency signal.

12. The device according to claim 11, wherein said second arc fault detecting means comprises:

current measurement means for sensing said level of AC current flowing through the load;

high frequency circuit means for generating said peak and average high frequency signals, wherein said peak high frequency signal corresponds to a peak level of high frequency current flowing through the load, and wherein said average high frequency signal corresponds to an average level of high frequency current flowing through the load;

AC line frequency circuit means for generating said peak and average AC line frequency signals, wherein said Peak AC line frequency signal corresponds to a peak level of AC line frequency current flowing through the load, and wherein said average AC line frequency signal corresponds to an average level of AC line frequency current flowing through the load; and

means for generating said signal level trigger signal.

13. The device according to claim 2, wherein said means for generating said signal level trigger signal generates said signal level trigger signal when either said peak high frequency signal exceeds a predetermined threshold or said peak AC line frequency signal exceeds a predetermined threshold.

14. The device according to claim 12, wherein said means for generating said signal level trigger signal generates said signal level trigger signal when either said average high frequency signal exceeds a predetermined threshold or said average AC line frequency signal exceeds a predetermined threshold.

15. The device according to claim 12, wherein said means for generating said signal level trigger signal generates said signal level trigger signal after a time delay, said time delay being dependent upon a level of arcing detected or on said level of AC line current detected.

16. The device according to claim 12, wherein said means for generating said signal level trigger signal generates said signal level trigger signal based on a plurality of arc fault trip levels which are dependent on a magnitude of said average AC line current.

17. The device according to claim 12, wherein said means for generating said signal level trigger signal generates said signal level trigger signal based on a plurality of arc fault trip levels which are dependent on said level of AC line current detected.

18. The device according to claim 12, further comprising means for simultaneously detecting peak and average magnitudes of said high frequency current and said AC line current.

19. The device according to claim 11 further comprising means for at least partially disabling at least one of said first and second arc fault detecting means for a finite period of time to permit a user to use an electrical device exhibiting arcing, and for enabling said disabled arc fault detecting means after use of the electrical device exhibiting arcing has been discontinued.

20. The device according to claim 11, further comprising means for receiving an external disable command and disabling at least one of said first and second arc fault detecting means.

21. The device according to claim 11, further comprising means for manually disabling and enabling at least one of said first and second arc fault detecting means.

22. The device according to claim 11, further comprising means for disabling at least one of said first and second arc fault detecting means during daylight hours, and for enabling said at least one disabled arc fault detecting means during night hours.

23. The device according to claim 11, further comprising means for disabling and enabling at least one of said first and second arc fault detecting means in accordance with signals received from a remote transmitter.

24. The device according to claim 1, further comprising fault detection means for detecting a fault other than an arc fault, and for activating said trigger means when a fault other than an arc fault is detected.

25. The device according to claim 24, wherein said fault detection means comprises ground fault circuit interrupter means for detecting the occurrence of a ground fault, and for generating a ground fault trigger signal in response to the detection of a ground fault.