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

• US 20080106269A1
• 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: Cosby, Thomas, Lewinski, Artur, Teggatz, Ross
• Granted Patent: US 8,018,235 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 3/33 using summation current transformers H02H3/347 takes precedence
• CPC Class Codes: H02H 3/335 the main function being self testing of the device

Abstract

Methods and apparatus to facilitate ground fault detection with a single coil and an oscillator are disclosed. An example ground fault detection device includes a sense coil including a secondary winding surrounding a line conductor and a neutral conductor, the line conductor and the neutral conductor forming a primary winding. The example ground fault detection device also includes a voltage oscillator connected in series with the secondary winding to drive an oscillation component, and at least one of a detector or an amplifier connected in series with the secondary winding to detect at least one of a neutral-to-ground fault or a line-to-ground fault.

Claims

1. A ground fault detection device comprising:

a sense coil comprising a secondary winding surrounding a line conductor and a neutral conductor, the line conductor and the neutral conductor forming a primary winding;

a voltage oscillator connected in series with the secondary winding to drive an oscillation component; and

at least one of a detector or an amplifier connected in series with the secondary winding to detect at least one of a neutral-to-ground fault or a line-to-ground fault.

2. A ground fault detection device as defined in claim 1, wherein the at least one detector or amplifier monitors a current of the secondary winding to detect the neutral-to-ground fault or the line-to-ground fault, the at least one detector or amplifier comprising at least one of a current detector or a voltage detector.

3. A ground fault detection device as defined in claim 1, wherein the detector separates the oscillation component from an induced current of the secondary winding to distinguish between the neutral-to-ground fault or the line-to-ground fault.

4. A ground fault detection device as defined in claim 3, wherein the detector comprises a neutral-to-ground detector to detect a current increase, the current increase indicative of a neutral-to-ground fault.

5. A ground fault detection device as defined in claim 3, wherein the detector comprises a line-to-ground detector to detect a current difference of the line conductor and the neutral conductor at a power-line frequency.

6. A ground fault detection device as defined in claim 1, wherein the at least one detector comprises a line-to-ground fault detector comprising a low pass filter.

7. A ground fault detection device as defined in claim 6, wherein the low pass filter blocks the oscillation component of the oscillator.

8. A method to detect a ground fault comprising:

driving a secondary winding of a sense coil in series with an oscillator, the sense coil comprising a primary winding formed by a line conductor and a neutral conductor, the secondary winding driven at an oscillation frequency by the oscillator;

detecting a current signal of the secondary winding;

comparing the detected current signal with a threshold to determine a neutral-to-ground fault;

filtering the detected current signal with a low pass filter; and

detecting a magnitude of the filtered current signal to determine a line-to-ground fault.

9. A method as defined in claim 8, wherein filtering the detected current signal comprises filtering the oscillation frequency generated by the oscillator.

10. A method as defined in claim 9, further comprising comparing the filtered current signal to detect a differential signal between the line conductor and the neutral conductor.

11. A method as defined in claim 10, further comprising activating a switch driver when the differential signal is detected, the differential signal indicative of a line-to-ground fault.

12. A method as defined in claim 11, wherein the activated switch driver causes at least one of illuminating a fault indicator or opening a relay to disconnect the line conductor and the neutral conductor from a load.

13. A method as defined in claim 8, further comprising activating a fault indicator signal when the detected fault causes the detected current signal to exceed the threshold.

14. A method as defined in claim 13, wherein the activated fault indicator signal causes at least one of illuminating a light emitting device or opening a relay to disconnect the line conductor and the neutral conductor.

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

drive a secondary winding of a sense coil in series with an oscillator, the sense coil comprising a primary winding formed by a line conductor and a neutral conductor, the secondary winding driven at an oscillation frequency by the oscillator;

detect a current signal of the secondary winding;

compare the detected current signal with a threshold to determine a neutral-to-ground fault;

filter the detected current signal with a low pass filter; and

detect a magnitude of the filtered current signal to determine a line-to-ground fault.

16. An article of manufacture as defined in claim 15, wherein the machine accessible instructions, when executed, cause the machine to filter the oscillation frequency generated by the oscillator.

17. An article of manufacture as defined in claim 16, wherein the machine accessible instructions, when executed, cause the machine to detect a differential signal between the line conductor and the neutral conductor.

18. An article of manufacture as defined in claim 17, wherein the machine accessible instructions, when executed, cause the machine to activate a switch driver when the differential signal is detected, the differential signal indicative of a line-to-ground fault.

19. An article of manufacture as defined in claim 18, wherein the machine accessible instructions, when executed, cause the machine to at least one of illuminate a fault indicator or open a relay to disconnect the line conductor and the neutral conductor from a load.

20. An article of manufacture as defined in claim 15, wherein the machine accessible instructions, when executed, cause the machine to activate a fault indicator signal when the detected fault causes the detected current signal to exceed the threshold.