Methods and apparatus for continuous ground fault self-test

• US 9,239,368 B2
• Filed: 01/23/2013
• Issued: 01/19/2016
• Est. Priority Date: 11/02/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Lewinski, Artur J., Teggatz, Ross, Cosby, Thomas E.
• Primary Examiner(s): NATALINI, JEFF WILLIAM
• Application Number:
  US13/748,343
• Publication Number:
  US 20130141110A1
• Time in Patent Office: 1,091 Days
• Field of Search: 324/509
• US Class Current: 1/1
• 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 method to continually 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 for the ground fault detection circuit to cause a first current imbalance in a sense coil for a first half of a power-line cycle;

diverting the current for the ground fault detection circuit 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, wherein causing the first current imbalance comprises;

diverting the current from the neutral conductor at a first location, the first location being between a powerline input to the ground fault detector and the sense coil location; and

returning the current to the line conductor at a second location being between the sense coil and an output of the ground fault detector.

2. A method as defined in claim 1, wherein causing the second current imbalance comprises:

diverting the current from the line conductor at a second location, the second location being between the sense coil and an output of the ground fault detector; and

returning the current to the neutral conductor at a first location being between a powerline input to the ground fault detector and the sense coil location.

3. A method as defined in claim 1, wherein monitoring for the first and second current imbalances comprises comparing the first and second current imbalances to a threshold equal to the expected current drawn by the ground fault detection circuit.

4. A method as defined in claim 3, further comprising determining a successful self-test if the first and second current imbalance are below the threshold.

5. An article of manufacture storing machine accessible instructions which, when executed, cause a machine to continually test a ground fault detector circuit:

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

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

divert the current for the ground fault detection circuit 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, 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 being between a powerline input to the ground fault detector and the sense coil location; and

return the current to the line conductor at a second location being between the sense coil and an output of the ground fault detector the sense coil location.

6. An article of manufacture as defined in claim 5, 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 being between the sense coil and an output of the ground fault detector the sense coil location; and

return the current to the neutral conductor at a first location being between a powerline input to the ground fault detector and the sense coil location.

7. An article of manufacture as defined in claim 5, wherein the machine accessible instructions, when executed, cause the machine to compare the first and second current imbalances to a threshold equal to the expected current drawn by the ground fault detection circuit.

8. An article of manufacture as defined in claim 7, wherein the machine accessible instructions, when executed, cause the machine to determine a successful self-test if the first and second current imbalance are below the threshold.