METHODS AND APPARATUS FOR CONTINUOUS GROUND FAULT SELF TEST

• US 20080106831A1
• 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 8,384,392 B2
• Time in Patent Office: Days
• US Class Current: 361/42
• CPC Class Codes: G01R 35/00 Testing or calibrating of apparatus covered by the other groups of this subclass
• CPC Class Codes: H02H 3/335 the main function being self testing of the device

Abstract

Methods and apparatus for continuous ground fault self-test 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 comprising a winding influenced by a current difference between the line conductor and the neutral conductor. The example ground fault detection device also includes a current bypass to facilitate a continuous current imbalance detected by the sense coil, and a ground fault detector circuit to detect at least one of the continuous current imbalance in the sense coil or a ground fault current imbalance.

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 winding influenced by a current difference between the line conductor and the neutral conductor;

a current bypass to facilitate a continuous current imbalance detected by the sense coil; and

a ground fault detector circuit to detect at least one of the continuous current imbalance in the sense coil or a ground fault current imbalance.

2. A ground fault detection device as defined in claim 1, wherein the ground fault detector circuit detects the continuous current imbalance in the sense coil and the ground fault current imbalance simultaneously.

3. A ground fault detection device as defined in claim 1, wherein the current bypass at least one of provides power to the ground fault detector or provides a fault simulation current.

4. A ground fault detection device as defined in claim 1, wherein the continuous current imbalance is proportional to a quiescent current of the ground fault detector circuit.

5. A ground fault detection device as defined in claim 1, wherein the current bypass further comprises a first power tap to at least one of provide power to the ground fault detector circuit or provide the continuous current imbalance to simulate a fault during a first half of a power-line cycle.

6. A ground fault detection device as defined in claim 5, wherein the first power tap comprises:

a first diode connected at a first location along one of the line conductor or the neutral conductor, the first location preceding the sense coil; and

a second diode connected at a second location along the other of the neutral conductor or the line conductor, the second location after the sense coil.

7. A ground fault detection device as defined in claim 6, wherein the current bypass further comprises a second power tap to at least one of provide power to the ground fault detector circuit or provide the continuous current imbalance to simulate the fault during a second half of the power-line cycle.

8. A ground fault detection device as defined in claim 7, wherein the second power tap comprises:

a third diode connected at the second location along one of the neutral conductor or the line conductor; and

a fourth diode connected at the first location along the other of the line conductor or the neutral conductor.

9. A ground fault detection device as defined in claim 1, wherein the ground fault detector circuit comprises a fault separation circuit to determine if the continuous current imbalance in the sense coil is associated with at least one of a ground fault detector circuit power drain, a continuous simulated fault, or a real ground fault.

10. A ground fault detection device as defined in claim 9, wherein the fault separation circuit comprises a self-test detector to compare the current imbalance with a threshold, the self-test detector to provide a fault signal when the current imbalance is below the threshold.

11. A ground fault detection device as defined in claim 10, wherein the self-test detector comprises a comparator.

12. A ground fault detection device as defined in claim 9, wherein the fault separation circuit comprises a subtractor and a normal-fault detector, the subtractor to generate a result by subtracting a simulated fault current from a total detected current imbalance, the normal-fault detector comparing the result to a threshold, the normal-fault detector to provide a fault signal when the result is greater than the threshold.

13. A ground fault detection device as defined in claim 12, wherein the normal-fault detector comprises a comparator.

14. A method to self-test a ground fault detector comprising:

continuously drawing current for a ground fault detector circuit from a line conductor and a neutral conductor;

diverting the current to cause a first current imbalance in a sense coil for a first half of a power-line cycle;

diverting the current to cause a second current imbalance in the sense coil for a second half of the power-line cycle; and

monitoring a secondary winding of the sense coil for the current imbalance caused by at least one of the first and second current imbalance or a signal indicative of a fault.

15. A method as defined in claim 14, wherein causing the first current imbalance comprises:

diverting the current from the neutral conductor at a first location, the first location preceding the sense coil location; and

returning the current to the line conductor at a second location after the sense coil location.

16. A method as defined in claim 14, wherein causing the second current imbalance comprises:

diverting the current from the line conductor at a second location, the second location after the sense coil location; and

returning the current to the neutral conductor at a first location preceding the sense coil location.

17. A method as defined in claim 14, wherein monitoring for the first and second current imbalances comprises comparing the first and second current imbalances to a threshold.

18. A method as defined in claim 17, further comprising determining a successful self-test if the first and second current imbalance exceed the threshold.

19. An article of manufacture storing machine accessible instructions which, when executed, cause a machine to:

continuously draw current for a ground fault detector circuit from a line conductor and a neutral conductor;

divert the current to cause a first current imbalance in a sense coil for a first half of a power-line cycle;

divert the current to cause a second current imbalance in the sense coil for a second half of the power-line cycle; and

monitor a secondary winding of the sense coil for the current imbalance caused by at least one of the first and second current imbalance or a signal indicative of a fault.

20. An article of manufacture as defined in claim 19, wherein the machine accessible instructions, when executed, cause the machine to:

divert the current from the neutral conductor at a first location, the first location preceding the sense coil location; and

return the current to the line conductor at a second location after the sense coil location.

21. An article of manufacture as defined in claim 19, wherein the machine accessible instructions, when executed, cause the machine to:

divert the current from the line conductor at a second location, the second location after the sense coil location; and

return the current to the neutral conductor at a first location preceding the sense coil location.

22. An article of manufacture as defined in claim 19, wherein the machine accessible instructions, when executed, cause the machine to compare the first and second current imbalances to a threshold.

23. An article of manufacture as defined in claim 20, wherein the machine accessible instructions, when executed, cause the machine to determine a successful self-test if the first and second current imbalance exceed the threshold.