Methods and apparatus to minimize saturation in a ground fault detection device

• US 8,311,785 B2
• Filed: 10/24/2007
• Issued: 11/13/2012
• 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 Edward
• Primary Examiner(s): Shah, Kamini S
• Assistant Examiner(s): Luu, Cuong
• Application Number:
  US11/923,354
• Publication Number:
  US 20080109193A1
• Time in Patent Office: 1,847 Days
• Field of Search: 703/4, 330/300, 330/260, 330/257, 455/339, 716/100, 327/524, 327/103, 327/110, 361/45, 361/50, 361/44, 361/144
• US Class Current: 703/4
• CPC Class Codes: G06F 30/367 Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods

Abstract

Methods and apparatus to minimize saturation in a ground fault detection device are disclosed. An example method includes connecting a capacitor simulator to a node of the ground fault detector device to prevent saturation, and monitoring power-line conductors for ground fault conditions with the ground fault detector device. An example apparatus to simulate a saturation capacitance in a ground fault device includes a sense coil induced by power-line conductors, and at least one of an amplifier or a current detector including an input connected to the sense coil and an output connected to a ground fault detector. The example apparatus also includes a saturation capacitor simulator connected to a node of at least one of the amplifier or the current detector to prevent saturation.

Claims

1. In a ground fault detection device comprising a transformer having a primary coil couplable to a power-line conductor and a secondary coil coupled to a detection circuit, the detection circuit comprising:

a non-transitory computer readable medium containing computer readable instructions stored therein for causing a processor to;

couple a secondary coil of the transformer to a first impedance converting circuit having a first pair of transconductance circuits and a first capacitor;

couple a second impedance converting circuit having a second pair of transconductance circuits and a second capacitor in parallel with the first capacitor, wherein the second impedance converting circuit converts the second capacitor into an inductor in parallel with the first capacitor;

convert, in the first impedance converting circuit, the parallel inductor and capacitor into a series connected inductance and capacitance, wherein the inductor becomes the capacitance and the capacitor becomes the inductance; and

measure an output of the first impedance converting circuit to detect a ground fault; and

couple a detector to the output of the first impedance converting circuit to detect a ground fault, wherein the detection circuit receives a signal containing current information and the detector measures the current as a voltage.

2. The detection circuit as defined in claim 1, wherein the computer readable instructions, when executed, cause the processor to connect an output of the ground fault device to at least one of disconnect the power-line conductors or illuminate a warning indicator upon receipt of the signal indicative of the ground fault.

3. A method of detecting a ground fault comprising:

coupling a power-line conductor to a primary coil of a transformer;

coupling a secondary coil of the transformer to a first impedance converting circuit having a first pair of transconductance circuits and a first capacitor;

coupling a second impedance converting circuit having a second pair of transconductance circuits and a second capacitor in parallel with the first capacitor, wherein the second impedance converting circuit converts the second capacitor into an inductor in parallel with the first capacitor;

converting, in the first impedance converting circuit, the parallel inductor and capacitor into a series connected inductance and capacitance, wherein the inductor becomes the capacitance and the capacitor becomes the inductance; and

measuring an output of the first impedance converting circuit in a detection circuit to detect a ground fault, wherein the detection circuit receives a signal containing current information and a detector measures the current as a voltage.

4. The method of claim 3 wherein the capacitance is an anti-saturation capacitance.

5. The method of claim 3 wherein the first pair of transconductance circuits comprises first and second transconductance circuits, the second pair of transconductance circuits comprises third and fourth transconductance circuits and the capacitance is equal to a product of the second capacitor, the first transconductance, and the second transconductance divided by a product of the third transconductance and the fourth transconductance.

6. The method of claim 3 further comprising activating a switch driver connected to the measuring circuit to at least one of activate a fault indicator or disconnect the power-line conductors.

7. The method of claim 4 wherein the first pair of transconductance circuits comprises first and second transconductance circuits, the second pair of transconductance circuits comprises third and fourth transconductance circuits and the capacitance is equal to a product of the second capacitor, the first transconductance, and the second transconductance divided by a product of the third transconductance and the fourth transconductance.

8. The method of claim 4 further comprising activating a switch driver connected to the detection circuit to at least one of activate a fault indicator or disconnect the power-line conductors.

9. In a ground fault detection device comprising a transformer having a primary coil couplable to a power-line conductor and a secondary coil coupled to a detection circuit, the detection circuit comprising:

a first impedance converting circuit having a first pair of transconductance circuits and a first capacitor and being coupled to the secondary coil;

a second impedance converting circuit having a second pair of transconductance circuits and a second capacitor coupled in parallel to the first capacitor, wherein the second impedance converting circuit converts the second capacitor into an inductor in parallel with the first capacitor, the first impedance converting circuit converting the parallel inductor and capacitor into a series connected inductance and capacitance, wherein the inductor becomes the capacitance and the capacitor becomes the inductance; and

a detector coupled to the output of the first impedance converting circuit to detect a ground fault, wherein the detection circuit receives a signal containing current information and the detector measures the current as a voltage.

10. The detection circuit of claim 9 wherein the capacitance is an anti-saturation capacitance.

11. The detection circuit as defined in claim 9, wherein the first pair of transconductance circuits comprises first and second transconductance circuits, the second pair of transconductance circuits comprises third and fourth transconductance circuits and the saturation capacitance is equal to a product of the capacitor, the first transconductance, and the second transconductance divided by a product of the third transconductance and the fourth transconductance.

12. The detection circuit as defined in claim 10, further comprising a switch driver connected to the ground fault detection device to at least one of activate a fault indicator or disconnect the power-line conductors.

13. The detection circuit as defined in claim 10, wherein the first pair of transconductance circuits comprises first and second transconductance circuits, the second pair of transconductance circuits comprises third and fourth transconductance circuits and the saturation capacitance is equal to a product of the capacitor, the first transconductance, and the second transconductance divided by a product of the third transconductance and the fourth transconductance.

14. The detection circuit as defined in claim 9, further comprising a switch driver connected to the ground fault detector to at least one of activate a fault indicator or disconnect the power-line conductors.