Ground impedance measurement of a conduit system

Patent metadata

Field	Value
Publication number	US-10451576-B2
Application number	US-201715483680-A
Country	US
Kind code	B2
Filing date	Apr 10, 2017
Priority date	Apr 11, 2016
Publication date	Oct 22, 2019
Grant date	Oct 22, 2019

Abstract

A system to determine the ground impedance of a conduit system includes a conductive sheath and a resistor of known value. The conductive sheath is configured to surround a portion of a conductor housed within a conduit system. Capacitive coupling occurs between the sheath and the conductor to establish a voltage source. The resistor is electrically coupled between the voltage source and a metal component of the conduit system, and a voltage drop is read across the resistor to determine the health of the ground impedance of the conduit system.

First claim

What is claimed is:

1. A system to determine the ground impedance of a conduit system, the system comprising:
a capacitive coupler, wherein the capacitive coupler includes a conductive tape wrapped a plurality of times around a first conductor housed within a conduit system to form a conductive sheath, wherein capacitive coupling occurs between the conductive sheath and the first conductor to establish a voltage source; and
a resistor of known value, the resistor electrically coupled between the capacitive coupler and a metal component of the conduit system, wherein a voltage across the resistor is representative of the ground impedance of the conduit system.

2. The system of claim 1 , wherein a voltage across the resistor of less than an ideal voltage but greater than a zero voltage indicates a weakening ground impedance of the conduit system.

3. The system of claim 2 , wherein the weakening ground impedance of the conduit system alerts to a corrosion state of the conduit system.

4. The system of claim 1 , further comprising an indicator coupled to the resistor, the indicator configured to provide an indication of the weakening ground impedance.

5. The system of claim 1 , further comprising a measurement device configured to measure the voltage across the resistor.

6. The system of claim 5 , wherein the measurement device is powered inductively by a second conductor within the conduit system, the second conductor different from the first conductor.

7. The system of claim 6 , wherein a clamp-on current transformer is coupled between the second conductor and the measurement device to inductively power the measurement device.

8. A method for determining ground impedance of a conduit system, the method comprising:
accessing a first conductor housed within a conduit system;
wrapping a conductive tape a plurality of times about the first conductor to form a capacitive coupler such that capacitive coupling occurs between the conductive tape and the first conductor, the capacitive coupling operating to establish a voltage source;
coupling a resistor of known value between the capacitive coupler and a metal component of the conduit system; and
measuring a voltage drop across the resistor, wherein the voltage drop is representative of the ground impedance of the conduit system.

9. The method of claim 8 , wherein a voltage across the resistor of less than an ideal voltage, but greater than a zero voltage, indicates a weakening ground impedance of the conduit system.

10. The method of claim 9 , further comprising providing an indication of the weakening ground impedance of the conduit system.

11. The method of claim 10 , wherein the indication of the weakening ground impedance provides an alert to corrosion within the conduit system.

12. The method of claim 8 , wherein the step of measuring is performed by a measurement device inductively powered by a second conductor housed within the conduit system, wherein the first conductor is different from the second conductor.

13. The method of claim 12 , wherein a clamp-on current transformer is coupled between the second conductor and the measurement device to inductively power the measurement device.

14. The method of claim 8 , wherein the conductor is an insulated conductor.

15. A method to determine the ground impedance of a conduit system, the method comprising:
calculating an impedance of the conduit system based on:
a voltage of a voltage source formed by a capacitive coupling between a first conductor and a coupler having a known impedance value;
a known resistance value of a resistor in communication between the voltage source and a metal component of the conduit system;
a voltage to ground value for the conduit system; and
a measured voltage drop across the resistor;

determining whether the impedance of the conduit system exceeds a failure threshold; and
in response to determining that the impedance exceeds the failure threshold, generating a ground fault alert.

16. The method of claim 15 , further comprising:
in response to determining that the impedance no longer exceeds the failure threshold, clearing the ground fault alert.

17. The method of claim 15 , wherein the measured voltage drop across the resistor is measured by a measurement device inductively powered by a second conductor housed within the conduit system, wherein the first conductor is different from the second conductor.

18. The method of claim 15 , wherein the coupler having the known impedance value is a conductive tape wrapped a plurality of times about the first conductor to form a conductive sheath.

Assignees

• Eaton Intelligent Power Ltd

Inventors

• Freer Benjamin Avery
• Manahan Joseph Michael

Classifications

• G01N17/02

  Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement · CPC title

• G01R27/18 Primary

  Measuring resistance to earth {, i.e. line to ground} · CPC title

• G08B21/185

  Electrical failure alarms · CPC title

• G08B21/182

  Level alarms, e.g. alarms responsive to variables exceeding a threshold · CPC title

• G01N27/20 Primary

  Investigating the presence of flaws · CPC title