Methods and apparatus to manage ground fault conditions with a single coil

• US 7,973,535 B2
• Filed: 10/20/2010
• Issued: 07/05/2011
• Est. Priority Date: 11/02/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Cosby, Thomas E., Teggatz, Ross, Lewinski, Artur J.
• Primary Examiner(s): Nguyen; Vincent Q
• Application Number:
  US12/908,684
• Publication Number:
  US 20110032646A1
• Time in Patent Office: 258 Days
• Field of Search: 324/509, 324/522, 324/616, 361/42, 361/46, 361/48
• 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 method of detecting a ground fault comprising:

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

monitoring a virtual inductor signal to determine at least one of a neutral-to-ground fault, a line-to-ground fault, or a non-fault condition, the virtual inductor comprising a voltage-to-current converter and a capacitor; and

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

2. A method as defined in claim 1, 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.

3. A method as defined in claim 1, 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.

4. A method as defined in claim 1, wherein monitoring the inductor signal comprises filtering the resonance signal component to detect the line-to-ground fault.

5. A method as defined in claim 4, further comprising determining whether the filtered resonance signal component comprises a power line frequency signal.

6. A method as defined in claim 5, further comprising generating the fault signal when the power line frequency signal is detected, the power line frequency signal indicative of the line-to-ground fault.

7. A method as defined in claim 1, wherein the voltage-to-current converter comprises an operational amplifier.

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

drive a first capacitor with a virtual inductor, the virtual inductor comprising a voltage-to-current converter and a capacitor, to generate a resonance signal component;

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

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

9. An article of manufacture as defined in claim 8, wherein the machine accessible instructions, when executed, cause the machine to detect 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.

10. An article of manufacture as defined in claim 8, wherein the machine accessible instructions, when executed, cause the machine to:

compare the resonance signal component to a threshold; and

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

11. An article of manufacture as defined in claim 8, wherein the machine accessible instructions, when executed, cause the machine to filter the resonance signal component to detect the line-to-ground fault.

12. An article of manufacture as defined in claim 11, wherein the machine accessible instructions, when executed, cause the machine to determine whether the filtered resonance signal component comprises a power line frequency signal.

13. An article of manufacture as defined in claim 12, wherein the machine accessible instructions, when executed, cause the machine to generate the fault signal when the power line frequency signal is detected, the power-line signal indicative of the line-to-ground fault.

14. An article of manufacture as defined in claim 8, wherein, the voltage-to-current converter comprising an operational amplifier and a capacitor.