Method of detecting wear in a pump driven with a frequency converter

1. A method of detecting wear of a pump, which pump is controlled with a frequency converter providing rotational speed and torque estimates, and characteristic curves of the pump being known, the method comprising:

obtaining a value representing an operating point of the pump by measuring flow (Q act ) or head (H act ) produced by the pump;

estimating, in a processor, the operating point of the pump by using a calculation based on characteristic curves of the pump and estimated rotational speed (n est ) of the pump and estimated torque (T est ) of the pump;

calculating, in the processor, an estimation error from a measured value representing the operating point and from the estimated operating point;

repeating the obtaining, estimating and calculating during operation of the pump; and

detecting, in the processor, wear of the pump from an amplitude of the estimation error.

2. A method according to claim 1 , wherein the obtaining of a value representing the operating point of the pump comprises:

obtaining a value, using a QH curve of the pump, representing flow (Q est,QH ) when the head produced by the pump is measured.

3. A method according to claim 2 , comprising:

estimating, in the processor, a flow (Q est,QP ) produced by the pump by using a QP curve-based estimation, the rotational speed, and torque estimates provided by the frequency converter, wherein the calculating of the estimation error comprises:

calculating, in the processor, a relative estimation error of the flow and a sign of the error, and wherein the detecting of the wear comprises:

detecting, in the processor, the wear of the pump from an amplitude of the relative estimation and from a sign of the estimation error.

4. A method according to claim 3 , comprising:

detecting the wear of the pump when the sign of the estimation error stays the same in repeated measurements and the amplitude of the relative estimation error grows gradually in repeated measurements.

5. A method according to claim 1 , wherein the obtaining a value representing the operating point of the pump comprises:

using the measured flow as a value representing the operating point.

6. A method according to claim 5 , comprising:

measuring the flow produced by the pump with a portable measuring device.

7. A method according to claim 5 , comprising:

estimating, in the processor, a flow (Q est,QP ) produced by the pump by using a QP curve-based estimation, the rotational speed, and torque estimates provided by the frequency converter, wherein the calculating of the estimation error comprises:

calculating, in the processor, a relative estimation error of the flow and a sign of the error, and wherein the detecting of the wear comprises:

detecting, in the processor, the wear of the pump from an amplitude of the relative estimation and from a sign of the estimation error.

8. A method according to claim 7 , comprising:

detecting the wear of the pump when the sign of the estimation error stays the same in repeated measurements and the amplitude of the relative estimation error grows gradually in repeated measurements.

9. A method according to claim 8 , comprising:

measuring the flow produced by the pump with a portable measuring device.

10. A method according to claim 1 , wherein the obtaining of a value representing the operating point of the pump comprises:

using the measured head as a value representing the operating point, and wherein the estimating of the operating point of the pump comprises:

estimating the head of the pump by using estimated power calculated from the estimated rotational speed, and estimated torque and a PH curve of the pump, and the calculating the estimation error comprises:

calculating the estimation error between the estimated head and the measured head.

11. An arrangement for detecting wear of a pump controlled with a frequency converter providing rotational speed and torque estimates, characteristic curves of the pump being known, wherein the arrangement comprises:

means for obtaining a value representing an operating point of the pump by measuring flow (Q act ) or head (H act ) produced by the pump during operation; and

processing means for estimating the operating point of the pump with a calculation based on characteristic curves of the pump, estimated rotational speed (n est ) of the pump, and estimated torque (T est ) of the pump, repeatedly calculating an estimation error from the value representing the operating point and from the estimated operating point during pump operation, and detecting pump wear from an amplitude of an estimation error.

12. The arrangement of claim 11 , wherein the processing means provides an indication of pump wear.

13. The arrangement of claim 11 , wherein the obtaining means includes a flow meter.

14. The arrangement of claim 11 , in combination with a pump whose wear is to be detected and a frequency converter.

15. The arrangement of claim 14 , wherein the frequency converter is connected with the detecting means via a wireless communication link.

16. The arrangement of claim 11 , wherein the processing means includes a processor configured with program modules to perform the estimating, calculating, and detecting wherein the processor is connected with the obtaining means.