METHODS AND APPARATUS TO FACILITATE GROUND FAULT DETECTION WITH A SINGLE COIL

• US 20080106268A1
• Filed: 10/24/2007
• Published: 05/08/2008
• Est. Priority Date: 11/02/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Teggatz, Ross, Cosby, Thomas Edward, Lewinski, Artur J.
• Granted Patent: US 7,834,636 B2
• Time in Patent Office: Days
• US Class Current: 324/509
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• 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 3/162 for ac systems
• CPC Class Codes: H02H 3/33 using summation current transformers H02H3/347 takes precedence

Abstract

Methods and apparatus to facilitate ground fault detection with a single coil are disclosed. An example ground fault detection device includes a sense coil to detect current in a line conductor and a neutral conductor, the sense coil including a primary winding and a secondary winding. The example ground fault detector also includes a capacitor in parallel with the secondary winding and an inductor to form a resonance circuit having a resonance frequency and having a signal proportional to the current, the signal indicative of a ground fault condition.

An example method of detecting a ground fault includes driving a first capacitor with an inductor to generate a resonance signal component and monitoring an inductor signal to determine at least one of a neutral-to-ground fault, a line-to-ground fault, or a non-fault condition. The example method also includes generating a fault signal when at least one of the line-to-ground fault or the neutral-to-ground fault is detected.

Claims

1. A ground fault detection device comprising:

a sense coil to detect current in a line conductor and a neutral conductor, the sense coil comprising a primary winding and a secondary winding;

a first capacitor in parallel with the secondary winding; and

an inductor to form a resonance circuit having a resonance frequency and having a signal proportional to the current, the signal indicative of a ground fault condition.

3. A ground fault detection device as defined in claim 1, further comprising a driving source in parallel with the resonance circuit to drive the resonance circuit with a resonance frequency signal at an amplitude limited oscillation.

4. A ground fault detection device as defined in claim 3, wherein the driving source comprises a negative resistance.

5. A ground fault detection device as defined in claim 1, wherein the ground fault condition comprises at least one of a line-to-ground fault or a neutral-to-ground fault, the ground fault condition determined by measuring the inductor signal.

6. A ground fault detection device as defined in claim 1, wherein the inductor comprises at least one of a virtual inductor, or an active inductor.

7. A ground fault detection device as defined in claim 6, wherein the virtual inductor comprises at least one of a transconductor, an operational amplifier, or a transistor.

8. A ground fault detection device as defined in claim 6, wherein the virtual inductor comprises at least one transconductor and a second capacitor.

9. A ground fault detection device as defined in claim 1, further comprising at least one detector to monitor the inductor signal to determine the ground fault condition.

10. A ground fault detection device as defined in claim 9, wherein the at least one detector determines the ground fault condition is at least one of a line-to-ground fault or a neutral-to-ground fault.

11. A ground fault detection device as defined in claim 9, wherein the at least one detector monitors at least one of the resonance frequency, or a difference between the current in the line conductor and the current in the neutral conductor.

12. A ground fault detection device as defined in claim 8, wherein the at least one detector separates the inductor signal into a resonance frequency component and a line conductor frequency component.

13. A ground fault detection device as defined in claim 12, wherein the at least one detector comprises a low pass filter to remove the resonance circuit resonance frequency component.

2. A ground fault detection device as defined in claim 2, wherein the resonance circuit is a tank circuit.

14. A method of detecting a ground fault comprising:

driving a first capacitor with an inductor to generate a resonance signal component;

monitoring an inductor signal to determine at least one of a neutral-to-ground fault, a line-to-ground fault, or a non-fault condition; and

generating a fault signal when at least one of the line-to-ground fault or the neutral-to-ground fault is detected.

15. A method as defined in claim 14, wherein monitoring the inductor signal further comprises detecting at least one of an absence or an attenuation of the resonance signal component, the at least one of the absence or the attenuation of the resonance signal component indicative of the neutral-to-ground fault.

16. A method as defined in claim 14, wherein monitoring the inductor signal further comprises:

comparing the resonance signal component to a threshold; and

activating at least one of a switch or an indicator when the oscillation signal component is below the threshold.

17. A method as defined in claim 14, wherein monitoring the inductor signal comprises filtering the resonance signal component to detect the line-to-ground fault.

18. A method as defined in claim 17, further comprising determining whether the filtered resonance signal component comprises a power-line signal.

19. A method as defined in claim 18, further comprising generating the fault signal when the power-line signal is detected, the power-line signal indicative of the line-to-ground fault.

20. A method as defined in claim 18, wherein the power-line signal comprises a frequency.

21. A method as defined in claim 14, wherein monitoring the inductor signal comprises monitoring a virtual inductor, the virtual inductor comprising at least one of a voltage-to-current converter, an operational amplifier, or a capacitor.

22. (canceled)

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)