SYSTEMS AND METHODS FOR DETECTING MOTOR ROTOR FAULTS

• US 20120265457A1
• Filed: 02/07/2012
• Published: 10/18/2012
• Est. Priority Date: 04/15/2011
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Donolo, Marcos A.
• Granted Patent: US 9,151,802 B2
• Time in Patent Office: Days
• US Class Current: 702/58
• CPC Class Codes: G01R 31/343 in operation
• CPC Class Codes: H02P 29/0241 the fault being an overvoltage

Abstract

Systems and methods for detecting fault conditions in a rotor of an electric induction motor are disclosed. In certain embodiments, a method for detecting fault conditions may include sampling a plurality of currents from an electric induction motor to obtain a plurality of current data points, calculating a global maximum magnitude of the plurality of current data points in the frequency domain over a range of predetermined frequencies, calculating an average magnitude of the plurality of current data points in the frequency domain over the range of predetermined frequencies, and declaring a motor rotor fault condition based on a comparison between the average magnitude and a first predetermined threshold, a comparison between a difference between the global maximum magnitude and the average magnitude and a second predetermined threshold, and a comparison between the global maximum magnitude and at least a third predetermined threshold.

Claims

1. A method for detecting a fault condition in a rotor of an electric induction motor comprising:

sampling a plurality of currents from an electric induction motor to obtain a plurality of current data points;

calculating a global maximum magnitude of the plurality of current data points in the frequency domain over a range of predetermined frequencies;

calculating an average magnitude of the plurality of current data points in the frequency domain over the range of predetermined frequencies; and

declaring a motor rotor fault condition based on a comparison between the average magnitude and a first predetermined threshold, a comparison between a difference between the global maximum magnitude and the average magnitude and a second predetermined threshold, and a comparison between the global maximum magnitude and at least a third predetermined threshold.

2. The method of claim 1, wherein sampling the plurality of currents comprises:

sampling the plurality of currents with an analog-to-digital converter to generate a plurality of digitized currents;

calculating an alpha current components of the plurality of digitized currents;

squaring the alpha current components;

filtering the alpha current components with a low pass filter to generate filtered alpha current components;

generating the plurality of current data points based on the filtered alpha current components; and

storing the plurality of current data points.

3. The method of claim 2, wherein sampling the plurality of currents further comprises:

downsampling the filtered alpha current components to generate the plurality of current data points.

4. The method of claim 2, wherein the method further comprises:

multiplying each of the plurality of current data points by a corresponding element in a Hamming window.

5. The method of claim 4, wherein the method further comprises:

applying a fast-Fourier transform function to the plurality of current data points to generate the plurality of current data points in the frequency domain.

6. The method of claim 5, wherein the global maximum magnitude comprises a maximum magnitude of the plurality of current data points in the frequency domain over the range of predetermined frequencies.

7. The method of claim 5, wherein the average magnitude comprises an average magnitude of the plurality of current data points in the frequency domain over the range of predetermined frequencies.

10. The method of claim 1, wherein declaring a motor rotor fault condition is further based on a comparison between the global maximum magnitude and a fourth predetermined threshold.

11. The method of claim 10, wherein declaring a motor rotor fault condition is further based on a comparison between the global maximum magnitude and a fifth predetermined threshold.

13. The method of claim 1, wherein the method further comprises:

storing the declared motor rotor fault condition as a fault condition event comprising an associated date, time, maximum magnitude, and frequency.

12. The method of claim 12, wherein the first, second, third, fourth, and fifth predetermined thresholds are obtained through bench testing or simulating fault conditions in a rotor of an electric induction motor.

14. An intelligent electronic device comprising:

a processor; and

a non-transitory computer readable medium communicatively coupled to the processor storing executable instructions that, when executed by the processor, cause the processor to;

receive a plurality of analog currents from an electric induction motor to obtain a plurality of current data points;

calculate a global maximum magnitude of the plurality of current data points in the frequency domain over a range of predetermined frequencies;

calculate an average magnitude of the plurality of current data points in the frequency domain over the range of predetermined frequencies; and

declare a motor rotor fault condition based on a comparison between the average magnitude and a first predetermined threshold, a comparison between a difference between the global maximum magnitude and the average magnitude and a second predetermined threshold, and a comparison between the global maximum magnitude and at least a third predetermined threshold.

15. The intelligent electronic device of claim 14, wherein the executable instructions are further configured to cause the processor to:

convert the plurality of analog currents into a plurality of digitized currents;

calculate an alpha current components of the plurality of digitized currents;

square the alpha current components;

filter the alpha current components with a low pass filter to generate filtered alpha current components;

generate the plurality of current data points based on the filtered alpha current components; and

store the plurality of current data points.

16. The intelligent electronic device of claim 14, wherein the global maximum magnitude comprises a maximum magnitude of the plurality of current data in the frequency domain points over the range of predetermined frequencies.

17. The intelligent electronic device of claim 14, wherein the average magnitude comprises an average magnitude of the plurality of current data points in the frequency domain over the range of predetermined frequencies.

18. The intelligent electronic device of claim 14, wherein declaring a motor rotor fault condition is further based on a comparison between the global maximum magnitude and one or more additional predetermined thresholds.

19. The intelligent electronic device of claim 18, wherein the first, second, third, and one or more additional predetermined thresholds are obtained through bench testing or simulating fault conditions in a rotor of an electric induction motor.

20. The intelligent electronic device of claim 14, wherein the executable instructions are further configured to cause the processor to:

store the declared motor rotor fault condition as a fault condition event comprising an associated date, time, maximum magnitude, and frequency.