Fault detection system

• US 6,867,596 B1
• Filed: 01/23/2003
• Issued: 03/15/2005
• Est. Priority Date: 01/23/2003
• Status: Active Grant

• Current Assignee: Vermeer Manufacturing Company
• Original Assignee: McLaughlin Manufacturing Co Inc.
• Inventors: Mizuno, Morio
• Primary Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US10/350,967
• Time in Patent Office: 782 Days
• Field of Search: 324/512, 324520-533
• US Class Current: 324/528
• CPC Class Codes: G01R 31/083 in cables, e.g. underground
• CPC Class Codes: G01R 31/58 Testing of lines, cables or conductors testing of electric windings G01R31/72

Abstract

A system and method for fault detection including a transmitter adapted to transmit a composite signal on a buried cable so that fault leakage of the composite signal returns to the transmitter through the ground surrounding the buried cable. The composite signal is composed of a low frequency first component that alternates at a first frequency and that defines a phase, and a low frequency second component that alternates at a second frequency higher than the first frequency and that defines a duty cycle having a predetermined relationship with the phase of the first component. A receiver receives the composite signal from the probe and filters the first component, filters the second component, defines an alternating reference signal having a phase based on the duty cycle of the filtered second component, and compares the phase of the reference signal with the phase of the filtered first component.

Claims

1. A system for detecting faults in a cable disposed in a conducting medium, said system comprising:

a. a transmitter that applies a composite signal to the cable, wherein the composite signal comprises

a low frequency first component that alternates at a first frequency and that defines a phase, and

a low frequency second component that alternates at a second frequency higher than the first frequency and that defines a duty cycle having a predetermined relationship with the phase of the first component,

wherein the composite signal returns to the transmitter through the conducting medium from a fault in the cable;

b. a probe that, when inserted into the conducting medium proximate the cable, receives the composite signal leaked from the fault; and

c. receiver circuitry that receives the composite signal from the probe and that

filters the first component,

filters the second component,

defines an alternating reference signal having a phase based on the duty cycle of the filtered second component, and

compares the phase of the reference signal with the phase of the filtered first component.

2. The system as in claim 1, wherein the conducting medium is ground.

3. The system as in claim 1, wherein the frequency of each of the first component and the second component is within a range of 10 Hz to 45 kHz.

4. The system as in claim 3, wherein the frequency of the first component is 512 Hz.

5. The system as in claim 3, wherein the frequency of the second component is 9.5 kHz.

6. The system as in claim 1, wherein the duty cycle of the second component is 50%.

7. The system as in claim 1, wherein the second component is active during a high portion of the first component and is inactive during a low portion of the first component.

8. The system as in claim 1, wherein the amplitude of the reference signal is high when an amplitude of the first component is high and wherein an amplitude of the reference signal is low when the amplitude of the first component is low.

9. The system as in claim 1, wherein the filtered first component is

in phase with the phase of the reference signal when the probe is located between the transmitter and the fault location, and

out of phase with the phase of the reference signal when the probe is located beyond the fault location.

10. The system as in claim 1, the transmitter further comprising a first probe for introducing the composite signal onto the cable, and a second probe coupled to the conducting medium to create a return path for the composite signal to the transmitter.

11. The system as in claim 1, further comprising a display for displaying the result of the comparison of the phase of the reference signal to that of the phase of the filtered first component.

12. A system for detecting faults in an underground cable, said system comprising:

a. a transmitter that applies a composite signal to the cable, wherein the composite signal is comprised of

a low frequency first component that alternates at a first frequency and that defines a phase, and

a low frequency second component that alternates at a second frequency higher than the first frequency and that defines a duty cycle that transitions correspondingly with the phase of the first component,

 

wherein the composite signal returns to the transmitter through the ground from a fault in the cable;

b. a probe that, when inserted into the ground proximate the cable, receives the composite signal leaked from the fault; and

c. receiver circuitry that receives the composite signal from the probe and that

filters the first component,

filters the second component,

defines an alternating reference signal having a phase that transitions correspondingly to the duty cycle of the filtered second component, and

compares the phase of the reference signal with the phase of the filtered first component.

13. A system for detecting faults in a cable disposed in a conducting medium, said system comprising:

a. a transmitter that applies a composite signal to the cable, wherein the composite signal is comprised of

a first signal that alternates at a first frequency and that defines a phase, and

a second signal that alternates at a second frequency higher than the first frequency and that defines a duty cycle having a predetermined relationship with the phase of the first signal,

wherein the composite signal returns to the transmitter through the conducting medium from a fault in the cable;

b. a probe that, when inserted into the conducting medium, receives both the first signal and the second signal leaked from the fault to the conducting medium; and

c. receiver circuitry that receives both the first signal and the second signal from the probe and that

filters the first signal,

filters the second signal,

defines a third signal having a phase based on the duty cycle of the filtered second signal, and

compares the phase of the third signal with the phase of the filtered first signal.

14. The system as in claim 13, wherein the conducting medium is ground.

15. The system as in claim 13, wherein the frequency of each of the first signal and the second signal is within a range of 10 Hz to 45 kHz.

16. The system as in claim 15, wherein the frequency of the first signal is 512 Hz.

17. The system as in claim 15, wherein the frequency of the second signal is 9.5 kHz.

18. The system as in claim 13, wherein the duty cycle of the second signal is 50%.

19. The system as in claim 13, wherein the second signal is active during a high portion of the first signal and is inactive during a low portion of the first signal.

20. The system as in claim 13, wherein an amplitude of the third signal is high when an amplitude of the first filtered signal is high and wherein the amplitude of the third signal is low when the amplitude of the first filtered signal is low.

21. The system as in claim 13, wherein the filtered first signal is

in phase with the phase of the third signal when the probe is located between the transmitter and the fault location, and

out of phase with the phase of the third signal when the probe is located beyond the fault location.

22. The system as in claim 13, the transmitter further comprising a first probe for introducing the composite signal onto the cable, and a second probe coupled to the conducting medium to create a return path for the composite signal to the transmitter.

23. The system as in claim 13, further comprising a display for displaying the result of the comparison of the phase of the third signal with the phase of the filtered first signal.

24. A method for detecting faults in an underground cable, said method comprising the steps of:

a. applying a composite signal to the cable, wherein the composite signal is comprised of

a low frequency first component that alternates at a first frequency and that defines a phase, and

a low frequency second component that alternates at a second frequency higher than the first frequency and that defines a duty cycle having a predetermined relationship with the phase of the first component,

 

wherein the composite signal returns to the transmitter through the conducting medium from a fault in the cable;

b. inserting a probe into the ground so that the probe receives the composite signal leaked from the fault;

c. filtering the first component of the composite signal received by the probe;

d. filtering the second component of the composite signal received by the probe;

e. defining an alternating reference signal having a phase based on the duty cycle of the filtered second component; and

f. comparing the phase of the reference signal with the phase of the filtered first component.

25. The method as in claim 24, wherein the duty cycle of the second component is 50%.

26. The method as in claim 24, wherein the first component is a square wave.

27. The method as in claim 24, the method further comprising displaying the result of step (f).

28. The method as in claim 24, after step (f) the method further comprising generating a signal representative of the location of the receiving probe relative to the cable fault.

29. The method as in claim 28, the method further comprising displaying the location of the receiving probe.

30. A method for detecting faults in an underground cable, said method comprising the steps of:

a. applying a composite signal to the cable, wherein the composite signal is comprised of

a low frequency first signal that alternates at a first frequency and that defines a phase, and

a low frequency second signal that alternates at a second frequency higher than the first frequency and that defines a duty cycle that transitions correspondingly with the phase of the first signal,

 

wherein the composite signal returns to the transmitter through the ground from a fault in the cable;

b. inserting a probe into the ground proximate the cable so that the probe receives the composite signal leaked from the fault;

c. filtering the first signal of the composite signal received by the probe;

d. filtering the second signal of the composite signal received by the probe;

e. defining a third signal having a phase based on the duty cycle of the filtered second signal; and

f. comparing the phase of the third signal with the phase of the filtered first signal.

31. The method as in claim 30, wherein the duty cycle of the second signal is 50%.

32. The method as in claim 30, wherein the first component is a square wave.

33. The method as in claim 30, the method further comprising displaying the result of step (f).

34. The method as in claim 30, after step (f) the method further comprising generating a fourth signal representative of the location of the receiving probe relative to the cable fault.

35. The method as in claim 34, the method further comprising using the fourth signal to display the location of the receiving probe.