Arc fault circuit interrupter with upstream impedance detector

• US 20030156367A1
• Filed: 01/30/2003
• Published: 08/21/2003
• Est. Priority Date: 02/01/2002
• Status: Abandoned Application

• Current Assignee: Pass & Seymour (Legrand SA)
• Original Assignee: Pass & Seymour (Legrand SA)
• Inventors: Macbeth, Bruce F.
• Application Number:
  US10/354,661
• Publication Number:
  US 20030156367A1
• Time in Patent Office: Days
• US Class Current: 361/38
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 1/003 Fault detection by injection of an auxiliary voltage same for detection of earth fault currents H02H3/17; for monitoring earth connection H02H5/105
• CPC Class Codes: H02H 3/331 responsive to earthing of the neutral conductor H02H3/338 takes precedence
• 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
• CPC Class Codes: H02H 5/105 responsive to deterioration or interruption of earth connection for preventing switching-on H02H11/001

Abstract

An electrical protection device which protects an electrical power distribution system supplying voltage from a secondary winding of a transformer through an electrically conductive path to the protection device includes an impedance detector which measures the impedance of the path. When the impedance of the path exceeds a pre-determined threshold, the protection device produces a signal which is used to indicate a problem or interrupt the circuit. In a system approach, an overcurrent protection device is installed at an origin of a branch circuit for interrupting current when an overcurrent condition is present, while a fault protection device is installed at an outlet in the branch circuit. The fault protection device includes circuitry for measuring an impedance in the branch circuit and circuitry for producing a signal when the measured impedance exceeds a predetermined value. Such a system affords series fault and parallel arc fault protection to the branch circuit.

Claims

1. An electrical protection device, protective of an electrical power distribution system supplying voltage from a secondary winding of a transformer through an electrically conductive path to said protection device, comprising:

a plurality of line terminals which receive voltage from said electrically conductive path; and

an impedance detector for measuring an impedance of said path;

wherein when said impedance detected by said impedance detector exceeds a pre-determined threshold, said protection device produces a signal.

2. A device according to claim 1 wherein said power distribution system further includes a load, said protection device further comprising:

a plurality of load terminals for delivering voltage from said secondary winding of said transformer to said load; and

a plurality of interrupting contacts between said load terminals and said line terminals;

wherein said signal causes said interrupting contacts to disconnect said load terminals from said line terminals.

3. A device according to claim 2 wherein said protection device is an arc fault circuit interrupter.

4. A device according to claim 2 wherein said protection device is a combination arc fault circuit interrupter and ground fault circuit interrupter.

5. A device according to claim 4 wherein said ground fault circuit interrupter portion of said protection device includes said impedance detector.

6. A device according to claim 1 further comprising an indicia, wherein a presence of said signal causes said indicia to indicate.

7. A device according to claim 1 further comprising means for disabling said signal after a predetermined interval following appearance of supply voltage at said protection device.

8. A device according to claim 1 further comprising means for disabling said signal except during each of a plurality of specified intervals.

9. A device according to claim 1 further comprising means for distinguishing said detected impedance from electrical noise.

10. A device according to claim 1, wherein when said electrical power distribution system further includes an overcurrent device in said electrically conductive path between said protection device and said secondary winding of said transformer, said protection device further comprises communication means for enabling said signal from said protection device to communicate with said overcurrent device, thereby signaling said overcurrent device to interrupt said electrically conductive path.

11. A device according to claim 1, said protective device further comprises:

a zero cross detector for locating either a first plurality of zero crosses in a current in said electrically conductive path, or a second plurality of zero crosses in said voltage; and

means for restricting said impedance measurement to at least one pre-determined interval;

wherein said at least one pre-determined interval is located proximate said first or second plurality of zero crosses.

12. A system of protective devices, comprising:

an overcurrent protection device installed at an origin of a branch circuit for interrupting current when an overcurrent condition is present;

a fault protection device installed at an outlet in said branch circuit;

wherein said fault protection device includes measuring means for measuring an impedance in at least a portion of said branch circuit and means for producing a signal when said measured impedance exceeds a predetermined value;

wherein said system of protective devices affords series fault and parallel arc fault protection to at least a portion of said electrical branch circuit.

13. A system according to claim 12 further comprising means for tripping said overcurrent protection device when said predetermined value of impedance is exceeded in said branch circuit.

14. A system according to claim 13 wherein said electrical branch circuit has a load, and said fault protection device further comprises:

a plurality of line terminals for receiving voltage from said overcurrent protection device;

a plurality of load terminals connected to said load; and

a set of interrupting contacts between said load terminals and said line terminals;

wherein said signal causes said set of interrupting contacts to disconnect said load terminals from said line terminals.

15. A system according to claim 14 wherein said fault protection device is an arc fault circuit interrupter.

16. A system according to claim 14 wherein said fault protection device is a combination arc fault circuit interrupter and ground fault circuit interrupter.

17. A system according to claim 16 wherein said ground fault circuit interrupter portion of said fault protection device includes said means for measuring said impedance.

18. A system according to claim 12 and further comprising an indicia, wherein a presence of said signal causes said indicia to indicate.

19. A system according to claim 15 wherein said portion of said electrical branch circuit receiving series fault and parallel arc fault protection from said system of protective devices includes said electrical branch circuit between said fault protection device and said overcurrent protection device.

20. A system according to claim 12 wherein said fault protection device further comprises communication means for enabling said signal from said protection device to communicate with said overcurrent device, thereby signaling said overcurrent device to interrupt said electrically conductive path.

21. A system according to claim 12 wherein said fault protection device protects said electrical branch circuit from series arc faults associated with said overcurrent protection device.

22. A system according to claim 12, wherein said measuring means also measures a supply impedance in a supply circuit, said supply circuit extending between said overcurrent protection device and a secondary winding of a transformer upstream of said overcurrent protection device, said system of protective devices affording series arc fault protection to said supply circuit.

23. An ohmmeter device incorporated in an electrical protector of an electrical power distribution system for monitoring an unknown impedance comprising:

a voltage source which induces a test current signal through said unknown impedance, thereby causing a voltage drop signal; and

a comparator which determines if said voltage drop signal across said unknown impedance exceeds a predetermined threshold, whereupon said comparator sends a signal to said electrical protector.

24. A device according to claim 23 wherein said test current signals and said voltage drop signals that are asynchronous are rejected by said ohmmeter device.

25. A device according to claim 23 and further comprising a microprocessor, wherein said microprocessor determines a waveform of said voltage source.

26. In an electrical protection device, protective of an electrical power distribution system supplying voltage from a secondary winding of a transformer through an electrically conductive path to said protection device, wherein said device includes a plurality of line terminals which receive voltage from said electrically conductive path, a plurality of load terminals for delivering voltage from said secondary winding of said transformer to a load, and a plurality of interrupting contacts between said load terminals and said line terminals;

a method for protecting said electrical power distribution system, comprising the steps of;

measuring an impedance of said path; and

producing a signal when said measured impedance exceeds a pre-determined threshold;

wherein said signal causes said interrupting contacts to disconnect said load terminals from said line terminals.

27. In an electrical protection device, protective of an electrical power distribution system supplying voltage from a secondary winding of a transformer through an electrically conductive path to said protection device, wherein said device includes a plurality of line terminals which receive voltage from said electrically conductive path, and a plurality of load terminals for delivering voltage from said secondary winding of said transformer to a load;

a method for protecting said electrical power distribution system, comprising the steps of;

generating a voltage signal to produce a test current in at least a portion of said electrical power distribution system;

measuring a signal responsive to said voltage signal; and

comparing said measured signal against a pre-determined reference signal to determine a fault condition within said portion of said electrical power distribution system.

28. A method according to claim 27, further comprising the step of disconnecting said load terminals from said line terminals when said measured signal exceeds said pre-determined reference signal.

29. A method according to claim 27, further comprising said step of indicating said fault condition when said measured signal exceeds said predetermined reference signal.