Methods and apparatus to facilitate ground fault detection with a single coil

• US 7,834,636 B2
• Filed: 10/24/2007
• Issued: 11/16/2010
• 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.
• Primary Examiner(s): Nguyen; Vincent Q
• Application Number:
  US11/923,365
• Publication Number:
  US 20080106268A1
• Time in Patent Office: 1,119 Days
• Field of Search: 324/509, 361/46, 361/45
• 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

A ground fault detection device includes a sense coil including a primary winding and a secondary winding to detect current in a line conductor and a neutral conductor. It also includes a capacitor in parallel with the secondary winding and a virtual inductor to form a resonance circuit having a signal proportional to the current and being indicative of a ground fault condition.

Claims

1. A ground fault detection device comprising:

an input for a power line comprising a line conductor and a neutral conductor;

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

a first capacitor in parallel with the secondary winding; and

a virtual 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.

2. A ground fault detection device as defined in claim 1, wherein the resonance circuit is a tank circuit.

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 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.

5. A ground fault detection device as defined in claim 1, wherein the virtual inductor comprises an active inductor simulated by voltage to current converters and a capacitor.

6. A ground fault detection device as defined in claim 5, wherein the virtual inductor comprises at least one transconductor.

7. A ground fault detection device as defined in claim 6, wherein the at least one detector separates the inductor signal into a resonance frequency component and a line conductor frequency component.

8. A ground fault detection device as defined in claim 7, wherein the at least one detector comprises a low pass filter to remove the resonance circuit resonance frequency component.

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 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;

a driving source in parallel with the resonance circuit to drive the resonance circuit with a resonance frequency signal at an amplitude limited oscillation, wherein the driving source comprises a negative resistance.

13. 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;

wherein the inductor comprises at least one of a virtual inductor, or an active inductor and wherein the virtual inductor comprises at least one of a transconductor, an operational amplifier, or a transistor.