Method and apparatus for control and detection in resistance grounded electrical systems

• US 20030043515A1
• Filed: 06/20/2002
• Published: 03/06/2003
• Est. Priority Date: 06/20/2001
• Status: Active Grant

• Current Assignee: Post Glover Resistors, Inc. (Post Glover IPC Resistors, Inc.)
• Original Assignee: Post Glover Resistors, Inc. (Post Glover IPC Resistors, Inc.)
• Inventors: Brungs, William T., Yingling, Thomas R., Frushour, Douglas E.
• Granted Patent: US 6,888,708 B2
• Time in Patent Office: Days
• US Class Current: 361/42
• CPC Class Codes: H02H 3/044 Checking correct functioning of protective arrangements, e.g. by simulating a fault for differential current circuit breakers H02H3/335
• CPC Class Codes: H02H 9/08 Limitation or suppression of earth fault currents, e.g. Petersen coil

Abstract

A ground fault detector for use in resistance grounded electrical systems. In one embodiment, the system includes a digital processor to monitor an electrical parameter of the resistance to determine and indicate whether a ground fault has occurred. Data regarding the ground fault occurrence can then be digitally stored transmitted, or processed, such as by an external computer. In another embodiment, the ground fault detector includes a filter to remove the harmonic components of the monitored electrical parameter, to avoid false alarms. In addition, in another embodiment, the ground fault detector can also determine whether a high harmonic condition is present in the monitored electrical system. The phase of the electrical system can be grounded by pressing a test switch, thereby causing a ground fault and allowing the harmonic components of the signal in the electrical system to be monitored.

Claims

1. A ground fault detector for a resistance grounded electrical system, comprising:

a neutral input configured to be connected to the neutral conductor of an electrical system;

a ground input configured to be connected to the ground conductor of an electrical system that connects to the neutral conductor through a neutral grounding resistor;

a signal conditioning circuit connected to the neutral and ground inputs and adapted to provide a measure of an electrical parameter associated with the neutral grounding resistor;

an analog-to-digital converter configured to convert the measure to a digital signal; and

a digital processor configured to received the digital signal from the analog-to-digital converter and configured to execute a program to determine whether a ground fault has occurred based upon the level of the digital signal.

2. The detector as recited in claim 1, wherein the electrical parameter comprises at least one of the voltage across the resistor and the current through the resistor.

3. The detector as recited in claim 1, further comprising:

a switch configured to provide a locator signal into the electrical system when activated.

4. The detector as recited in claim 1, wherein the signal conditioning circuit comprises a notch filter circuit having an output providing a harmonic frequency signal of the electrical parameter, and wherein the processor is further adapted to determine whether the harmonic frequency signal exceeds a predetermined level.

5. The detector as recited in claim 4, wherein the signal conditioning circuit further comprises an RMS converter circuit configured to provide an RMS signal for the harmonic frequency signal and an RMS signal for the electrical parameter.

6. The detector as recited in claim 5, wherein the signal conditioning circuit further comprises a switch configured to switch between the RMS signal for the harmonic frequency signal and the RMS signal for the electrical parameter.

7. The detector as recited in claim 1, wherein the signal conditioning circuit further comprises an RMS converter circuit to provide the measure as an RMS signal.

8. The detector as recited in claim 1, further comprising:

a digital memory unit in communication with the processor and adapted to store ground fault limits parameters.

9. The detector as recited in claim 1, further comprising:

a display in communication with the processor and configured to display the parameters.

10. The detector as recited in claim 1, further comprising:

output indicators controlled by the digital processor to indicate a ground fault occurrence.

11. The detector as recited in claim 10, wherein the indicators comprise a ground fault alert indicator and a high harmonic alarm indicator.

12. A high resistance grounding system, comprising

a neutral conductor;

a phase conductor;

a ground connection;

a resistor having a high resistive impedance connected between the neutral conductor and the ground connection; and

a digital processor configured to determine whether a ground fault has occurred by monitoring an electrical parameter of the high resistance resistor.

13. The system as recited in claim 12, wherein the electrical parameter comprises at least one of a voltage and a current.

14. A ground fault detector system, comprising:

a resistor connected between the neutral and ground of a monitored electrical system;

a digital detection circuit configured to determine a ground fault condition from an electrical parameter of the resistor;

a digital communication link; and

a digital storage apparatus in communication with the digital detection circuit via the digital communication link and configured to receive signals from the digital detection circuit.

15. The system as recited in claim 14, wherein the storage apparatus comprises a general purpose computer.

16. The system as recited in claim 15, further comprising:

a software program configured to be executed by the personal computer, to modify parameters to be utilized by the digital detection circuit, and to communicate the parameters to the digital detection circuit.

17. The system as recited in claim 14, wherein the digital storage apparatus comprises a general purpose computer, the system further comprising:

an operator panel in communication with the digital detection circuit and having a display device configured to display parameters to be utilized by the digital detection circuit and an input device configured to allow for user inputs to modify the parameters; and

a software program configured to be executed by the general purpose computer and configured to mimic the appearance of the operator panel.

18. A ground fault detector system, comprising:

a neutral-to-ground resistor connected between the neutral and ground of a monitored electrical system;

a ground input configured to connect to the ground of the monitored electrical system;

a phase input configured to connect to the phase of the monitored electrical system; and

a detection circuit configured to determine a ground fault condition from an electrical parameter of the resistor and configured to detect a high harmonic condition of the electrical parameter.

19. The system as recited in claim 18, further comprising:

a filter configured to provide the harmonic components of the electrical parameter to the detection circuit.

20. The system as recited in claim 18, further comprising:

a test resistor; and

a test switch configured to connect the phase input to the ground input through the test resistor, wherein the detection circuit is configured to detect the high harmonic condition of the electrical parameter when the test switch is pressed.