Ground fault detection methods on variable frequency drive systems

Patent metadata

Field	Value
Publication number	US-11329589-B2
Application number	US-201313842707-A
Country	US
Kind code	B2
Filing date	Mar 15, 2013
Priority date	Mar 28, 2012
Publication date	May 10, 2022
Grant date	May 10, 2022

Abstract

A mining machine including a motor, an adjustable speed drive providing a voltage to the motor, the voltage having an excitation component comprising a magnitude and a frequency for operating the motor at a desired speed and including an additional voltage component for use in detecting a ground fault condition, and a ground fault relay for detecting a ground fault current when the ground fault current exceeds a predetermined threshold.

First claim

What is claimed is:

1. A mining machine comprising:
a motor; and
a ground fault relay including a ground fault relay controller and at least one current sensor; and
an adjustable speed drive including a variable frequency drive controller configured to control the adjustable speed drive to provide a voltage to the motor, the voltage having an excitation component including a magnitude and a frequency for operating the motor at a desired speed, the voltage further including an additional voltage component for use in detecting a ground fault condition, the additional voltage component modifying the ground fault current by increasing a magnitude of the ground fault current;
wherein the variable frequency drive controller receives an indication from the ground fault relay controller when the at least one current sensor detects a ground fault current that exceeds a predetermined threshold.

2. The mining machine of claim 1 , wherein the additional voltage signal is one of a low-frequency alternating current waveform and a direct current.

3. The mining machine of claim 1 , wherein the voltage is a three-phase voltage.

4. The mining machine of claim 1 , wherein each phase of the three-phase voltage includes the additional voltage signal.

5. The mining machine of claim 1 , wherein the adjustable speed drive is a variable-frequency drive.

6. The mining machine of claim 1 , wherein the motor is an alternating current motor.

7. A method for detecting a ground fault of a mining machine including a motor, an adjustable speed drive, and a ground fault relay, the method comprising:
generating, at the adjustable speed drive, a three-phase voltage for the motor, each phase of the three-phase voltage including an additional voltage signal, the additional voltage signal modifying a ground fault current;
providing, by the adjustable speed drive, the three-phase voltage to the motor;
detecting, by at least one current sensor of the ground fault relay, a ground fault current between the motor and the adjustable speed drive; and
outputting, by a ground fault relay controller of the ground fault relay, an indication of a ground fault when the at least one current sensor detects a ground fault current that exceeds a predetermined threshold.

8. The method of claim 7 , wherein the additional voltage signal modifies the ground fault current by increasing a magnitude of the ground fault current.

9. The method of claim 7 , wherein the additional voltage signal is one of a low-frequency alternating current waveform and a direct current.

10. A system for generating variable frequency voltage for an alternating current motor, the system comprising:
a variable frequency drive including a variable frequency drive controller electrically coupled to the variable frequency drive and configured to
control the variable frequency drive to generate a three-phase voltage for the alternating current motor;
control the variable frequency drive to generate an additional voltage signal, the additional voltage signal added onto each phase of the three-phase voltage to increase a magnitude of a ground fault current; and
control the variable frequency drive to provide the three-phase voltage injected with the additional voltage signal to the alternating current motor.

11. The system of claim 10 , further comprising a user interface configured to receive instructions from a user, the instructions including an operating speed for the motor.

12. The system of claim 11 , wherein the variable frequency drive controller is further configured to receive the instructions from the user interface and control the variable frequency drive to generate the three-phase voltage for the motor based on the instructions.

13. The system of claim 10 , further comprising a ground fault relay configured to measure the magnitude of a ground fault current with a current sensor of the ground fault relay, and output, with a ground fault relay controller, an indication of a ground fault to the variable frequency drive controller when the magnitude exceeds a predetermined value.

Assignees

• Joy Global Underground Mining Llc

Inventors

• Dalton Peter M
• Jordan Michael

Classifications

• H02H3/162 Primary

  for AC systems · CPC title

• H02H3/165

  for three-phase systems · CPC title

• H02P27/04 Primary

  using variable-frequency supply voltage, e.g. inverter or converter supply voltage · CPC title

• H02H3/17

  by means of an auxiliary voltage injected into the installation to be protected {(using summation current transformers H02H3/33)} · CPC title