System and method of detecting cavitation in pumps

Patent metadata

Field	Value
Publication number	US-9777748-B2
Application number	US-75393010-A
Country	US
Kind code	B2
Filing date	Apr 5, 2010
Priority date	Apr 5, 2010
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

A system and method for detecting cavitation in pumps for fixed and variable supply frequency applications is disclosed. The system includes a controller having a processor programmed to repeatedly receive real-time operating current data from a motor driving a pump, generate a current frequency spectrum from the current data, and analyze current data within a pair of signature frequency bands of the current frequency spectrum. The processor is further programmed to repeatedly determine fault signatures as a function of the current data within the pair of signature frequency bands, repeatedly determine fault indices based on the fault signatures and a dynamic reference signature, compare the fault indices to a reference index, and identify a cavitation condition in a pump based on a comparison between the reference index and a current fault index.

First claim

What is claimed is:

1. A controller configured to monitor pump cavitation having a processor programmed to:
repeatedly receive real-time operating current data from a motor driving a pump;
generate a current frequency spectrum from the current data;
analyze current data within a pair of signature frequency bands of the current frequency spectrum;
determine at least one fault signature from the current data within the pair of signature frequency bands;
determine at least one dynamic reference signature from the current frequency spectrum;
determine at least one fault index based on the at least one fault signature and the at least one dynamic reference signature;
compare the fault indices to a reference index; and
identify a cavitation condition based on a comparison between the reference index and a current fault index.

2. The controller of claim 1 wherein the processor is programmed to calculate the dynamic reference signature using current data from outside the pair of signature frequency bands and outside a supply frequency offset band.

3. The controller of claim 2 wherein the processor is programmed to apply a low-pass filter to the portion of the current frequency spectrum outside the pair of signature frequency bands and outside the signature offset band.

4. The controller of claim 1 wherein the processor is further programmed to calculate the reference index from a plurality of fault indices acquired over a period of operation of the motor.

5. The controller of claim 4 wherein the processor is further programmed to:
identify a pre-determined percentage of fault indices acquired over the period of operation of the motor having a smallest value; and
calculate a mean of the pre-determined percentage of fault indices acquired over the period of operation of the motor having the smallest value to generate the reference index.

6. The controller of claim 4 wherein the processor is further programmed to update the reference index after one of a preset time period of motor operation and a determination of a preset number of fault indices.

7. The controller of claim 6 wherein the processor is further programmed to update the reference index using a number of fault indices having values less than the reference index.

8. The controller of claim 7 wherein the processor is further programmed to:
determine if the number of fault indices having values less than the reference index is greater than a pre-determined percentage of a total number of fault indices from the one of the preset time period of motor operation and the preset number of fault indices; and
if the number of fault indices having values less than the cavitation threshold is greater than the pre-determined percentage of the total number of fault indices, then update the reference index.

9. The controller of claim 6 wherein the processor is programmed to:
scale the reference index; and
identify a cavitation condition if the current fault index is greater than the scaled reference index.

10. A method of detecting cavitation in a pump driven by an electric motor, the method comprising:
accessing motor current data corresponding to a motor controlled by a variable frequency drive;
generating modified motor current data having a fundamental frequency removed therefrom;
performing a frequency spectrum analysis on the modified motor current data to generate a plurality of current frequency spectrums;
generating a plurality of fault index samples from the plurality of current frequency spectrums over a period of operation of the motor, wherein a respective fault index sample of the plurality of fault index samples comprises a ratio of a current magnitude in a first portion of a respective current frequency spectrum to a current magnitude in a second portion of the respective current frequency spectrum;
calculating a cavitation threshold using historical fault index samples of the plurality of fault index samples; and
generating an alarm if a real-time fault index sample of the plurality of fault index samples is greater than the cavitation threshold.

11. The method of claim 10 further comprising conditioning the motor current data using a notch filter.

12. The method of claim 10 wherein performing a frequency spectrum analysis comprises performing an FFT on the motor current data.

13. The method of claim 10 wherein generating the plurality of fault index samples comprises:
determining a fault signature based on a maximum amplitude of a sub-portion of the modified frequency spectrum; and
comparing the fault signature to a reference floor.

14. The method of claim 10 further comprising calculating a reference floor to represent a non-cavitation condition, wherein calculating the reference floor comprises:
applying a low-pass filter to current data outside the sub-portion of the current frequency spectrum and outside a fundamental offset portion of the current frequency spectrum; and
calculating a mean value of the filtered current data.

15. The method of claim 10 further comprising continuously updating the cavitation threshold using real-time motor current data.

16. A non-transitory computer readable storage medium having stored thereon a computer program comprising instructions which, when executed by at least one processor, cause the at least one processor to:
receive current data from a sensor system coupled to a motor/pump system;
condition the current data;
generate a frequency spectrum of the current data;
extract a fault signature and a reference signature from the frequency spectrum, the fault signature and the reference signature representative of a load condition and an operating frequency of the motor/pump system;
calculate a fault index using the fault signature and the reference signature;
compare the fault index to a fault threshold; and
generate an alarm if the fault index is greater than the fault threshold.

17. The computer readable storage medium of claim 16 wherein the instructions that cause the at least one processor to extract the fault signature cause the at least one processor to define a pair of frequency side bands and a frequency offset band.

18. The computer readable storage medium of claim 17 wherein the instructions that cause the at least one processor to extract the fault signature further cause the at least one processor to calculate an average of current components in the pair of frequency side bands.

19. The computer readable storage medium of claim 16 wherein the instructions that cause the at least one processor to extract the reference signature cause the at least one processor to:
define a pair of frequency side bands and a frequency offset band corresponding to the frequency spectrum;
apply a low-pass filter to current data outside the pair of frequency side bands and the frequency offset band; and
calculate a mean value of the filtered current data.

20. The computer readable storage medium of claim 16 wherein the instructions, when executed by at least one processor, further cause the at least one processor to:
access a first plurality of fault indices from a first period of motor/pump operation;
calculate the fault threshold using a subset of the first plurality of fault indices;
access a second plurality of fault indices from a second period of motor/pump operation following the first period of motor/pump operation; and
update the fault threshold using a subset of the second plurality of fault indices.

21. A controller configured to mon

Assignees

• Lu Bin
• Sharma Santosh Kumar
• Yan Ting
• Dimino Steven A
• Eaton Corp

Inventors

• Lu Bin
• Sharma Santosh Kumar
• Yan Ting
• Dimino Steven A

Classifications

• F04D15/0077

  Safety measures (F04D15/02 takes precedence) · CPC title

• F04D15/0088

  Testing machines · CPC title

• F04D29/669 Primary

  especially adapted for liquid pumps (F04D29/18 takes precedence) · CPC title