Neutral grounding resistor monitor

Patent metadata

Field	Value
Publication number	US-2015048840-A1
Application number	US-201314386108-A
Country	US
Kind code	A1
Filing date	Apr 11, 2013
Priority date	Apr 12, 2012
Publication date	Feb 19, 2015
Grant date	—

Abstract

A device for monitoring a neutral grounding resistor (NGR), including first and second NGRs electrically connected in parallel, a rectifier circuit electrically connected in series with the second NGR and a voltage source and a logic resistor electrically connected in series with the second NGR. A logic circuit measures current passing through the logic resistor and determines the resistance of the first NGR based on the measured current and the resistance of the second NGR. As such, a failed-open or failed-short condition of the first NGR may be identified based at least in part on the determined resistance of the first NGR.

First claim

What is claimed is:

1 . An apparatus comprising:
a first neutral grounding resistor (NGR) and a second NGR electrically connected to a neutral conductor; a rectifier circuit electrically connected to the second NGR; a voltage source electrically connected to a logic resistor and the second NGR; and a logic circuit, the logic circuit operatively enabled to measure the current passing through the logic resistor.

2 . The apparatus of claim 1 , wherein the logic circuit is further operatively enabled to determine the resistance of the first NGR based at least in part on the measured current and the resistance of the second NGR.

3 . The apparatus of claim 2 , wherein the logic circuit is further operatively enabled to identify a failed-short condition with the first NGR based at least in part on the measured current and the determined resistance of the first NGR.

4 . The apparatus of claim 2 , wherein the logic circuit is further operatively enabled to identify a failed-open condition with the first NGR based at least in part on the measured current and the determined resistance of the first NGR.

5 . The apparatus of claim 1 , wherein the logic resistor is electrically connected in series with the second NGR.

6 . The apparatus of claim 1 , wherein the first and second NGR are electrically connected in parallel.

7 . The apparatus of claim 1 , wherein the rectifier circuit comprises a first diode and a second diode electrically connected in parallel.

8 . The apparatus of claim 7 , wherein the anode of the first diode is electrically connected to the cathode of the second diode.

9 . The apparatus of claim 8 , wherein the rectifier circuit is electrically connected in series with the second NGR and in parallel with the voltage source and the logic resistor.

10 . The apparatus of claim 1 , wherein the first NGR and the second NGR have substantially the same resistance.

11 . The apparatus of claim 1 , wherein the logic resistor has substantially less resistance than either the first NGR or the second NGR.

12 . The apparatus of claim 1 , wherein the voltage source is a direct-current voltage source.

13 . The apparatus of claim 12 , wherein the voltage source is a power supply circuit.

14 . An apparatus of claim for monitoring a first neutral grounding resistor (NGR) electrically connected to a neutral conductor, the apparatus comprising:
a second NGR electrically connected in parallel with the first NGR; a rectifier circuit electrically connected to the second NGR; a voltage source electrically connected in series with a logic resistor and the second NGR; and a logic circuit, the logic circuit operatively enabled to measure the current passing through the logic resistor and determine the resistance of the first NGR based at least in part on the measured current and the resistance of the second NGR.

15 . The apparatus of claim 14 , wherein the logic circuit is further operatively enabled to identify whether the first NGR has entered a failed-open or a failed-short condition based at least in part on the measured current and the determined resistance of the first NGR.

16 . The apparatus of claim 14 , wherein the rectifier circuit comprises a first diode and a second diode electrically connected in parallel and where the anode of the first diode is electrically connected to the cathode of the second diode.

17 . The apparatus of claim 14 , wherein the rectifier circuit is electrically connected in series with the second NGR and in parallel with the voltage source and the logic resistor.

18 . The apparatus of claim 14 , wherein the first NGR and the second NGR have substantially the same resistance.

19 . The apparatus of claim 14 , wherein the logic resistor has substantially less resistance than either the first NGR or the second NGR.

20 . A method for monitoring a first neutral grounding resistor (NGR) comprising:
measuring current flowing through a logic resistor, wherein the logic resistor is electrically connected in series with a voltage source and a second NGR, the second NGR being electrically connected in parallel with the first NGR; determining a resistance of the first NGR based at least in part on the measured current and a known resistance of the second NGR; and determining whether the first NGR has experienced a failed-open or a failed-short condition based at least in part on the determined resistance.

Assignees

• Vangool Michael P
• Baker Geoffrey J
• Littelfuse Inc

Inventors

• Vangool Michael P
• Baker Geoffrey J

Classifications

• H02H3/16

  responsive to fault current to earth, frame or mass (with balanced or differential arrangement H02H3/26 {; monitoring earth connection H02H5/105}) · CPC title

• H02H5/105

  responsive to deterioration or interruption of earth connection (for preventing switching-on H02H11/001) · CPC title

• G01R31/50 Primary

  Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections (testing of sparking plugs H01T13/58) · CPC title

• G01R31/025 Primary

  Physics · mapped topic