Two-wire resistance terminated ground check

Patent metadata

Field	Value
Publication number	US-2016245854-A1
Application number	US-201615047875-A
Country	US
Kind code	A1
Filing date	Feb 19, 2016
Priority date	Feb 19, 2015
Publication date	Aug 25, 2016
Grant date	—

Abstract

A ground check monitoring device coupled to a trailing cable includes a voltage source and a switch. The trailing cable includes a first conductor, a second conductor, and a ground conductor. A resistive termination device is coupled between the first conductor and the ground conductor. A controller of the ground check monitoring device can toggle the switch between a first node of the first conductor and a second node of the second conductor. By measuring voltages at the first and second nodes, the ground check monitoring device can determine if the resistive termination device is shorted. Further, the controller can calculate resistance values of the first and second conductors and calculate a resistance value of the ground conductor. The calculated resistance values can be compared to expected values and the controller can signal a ground fault condition as appropriate based on the comparisons.

First claim

1 . An apparatus, comprising:
a ground check monitoring device including a voltage source, a switch, and a controller for operating the switch, the ground check monitoring device having an internal sense resistance; a trailing cable including a first conductor, a second conductor, and a ground conductor, the first conductor having a first resistance, the second conductor having a second resistance, and the ground conductor having a third resistance, the trailing cable coupled to the ground check monitoring device; and a resistive termination device coupled between the first conductor and the ground conductor, wherein the controller couples the switch to the first conductor at a first node in a first state and couples the switch to the second conductor at a second node in a second state, wherein the controller measures voltages of the first and second nodes in the first and second states to determine when the resistive termination device is shorted.

2 . The apparatus of claim 1 , wherein the internal sense resistance represents an internal resistance of the ground check monitoring device.

3 . The apparatus of claim 1 , wherein the switch is coupled in series with the voltage source.

4 . The apparatus of claim 1 , wherein the ground conductor is coupled to the voltage source.

5 . The apparatus of claim 1 , wherein the first and second conductors are pilot wires.

6 . The apparatus of claim 1 , wherein a value of the first resistance is approximately equal to a value of the second resistance.

7 . The apparatus of claim 1 , wherein the controller determines the resistive termination device is shorted when the measured voltage of the second node when the switch is in the first state is approximately equal to the measured voltage of the first node when the switch is in the second state.

8 . The apparatus of claim 1 , wherein the controller determines the resistive termination device is shorted when the measured voltage of the second node when the switch is in the second state is approximately equal to the measured voltage of the first node when the switch is in the first state.

9 . The apparatus of claim 1 , wherein a value of the first resistance is approximately equal to a value of the second resistance and the controller calculates values of the first and second resistances and the third resistance based on the measured voltages of the first and second nodes, a known voltage value provided by the voltage source, a known value of the internal sense resistance, and a known resistance value of the resistive termination device.

10 . The apparatus of claim 9 , wherein the controller calculates values of the first and second resistances and the third resistance according to:

V

first



node

=

(

R

first
/
second

+

R
termination

+

R
third

)

R

first
/
second

+

R
termination

+

R
third

+

R
internal

*

V
source

V

second



node

=

(

R
third

)

R

first
/
second

+

R
termination

+

R
third

+

R
internal

*

V
source

where V first node is equal to the measured voltage of the first node when the switch is in the first state, V second node is the equal to the measured voltage of the second node when the switch is in the first state, V source is equal to the known voltage value provided by the voltage source, R first/second is equal to the value of one of the first or second resistances, R termination is equal to the known resistance value of the resistive termination device, R third is equal to the value of the third resistance, and R internal is equal to the known value of the internal sense resistance.

11 . The apparatus of claim 9 , wherein the controller calculates values of the first and second resistances and the third resistance according to:

V

first



node

=

(

R
third

)

R
third

+

R

first
/
second

+

R
internal

*

V
source

Assignees

• Littelfuse Inc

Inventors

• Vangool Michael
• El-Kharbawe Nehad El-Sherif
• Fenty George J

Classifications

• G01R31/58 Primary

  Testing of lines, cables or conductors (testing of electric windings G01R31/72) · CPC title

• G01R27/18

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

• H02H3/165

  for three-phase systems · CPC title

• G01R31/025 Primary

  Physics · mapped topic

• G01R31/021

  Physics · mapped topic