METHOD AND SYSTEM FOR DETECTING CAVITATION OF PUMP AND FREQUENCY CONVERTER

• US 20100143157A1
• Filed: 12/01/2009
• Published: 06/10/2010
• Est. Priority Date: 12/09/2008
• Status: Abandoned Application

• Current Assignee: Abb Oy (ABB Limited)
• Original Assignee: Abb Oy (ABB Limited)
• Inventors: AHONEN, Tero, AHOLA, Jero
• Application Number:
  US12/628,669
• Publication Number:
  US 20100143157A1
• Time in Patent Office: Days
• US Class Current: 417/44.100
• CPC Class Codes: F04D 15/0066 by changing the speed, e.g. of the driving engine
• CPC Class Codes: F04D 15/0088 Testing machines
• CPC Class Codes: F04D 29/669 especially adapted for liquid pumps F04D29/18 takes precedence

Abstract

A method and a system are disclosed in accordance with a pump controlled with a frequency converter. An exemplary method includes controlling the pump with a frequency converter, the frequency converter feeding a motor connected to drive the pump, providing a torque estimate (T_est) and/or a rotational speed estimate (n_est) of the motor from the frequency converter, forming one or more features (Feature1, Feature2, Feature3, Feature4) indicating cavitation or likelihood of cavitation of the pump and/or reverse flow of the pump using the provided estimates (T_est, n_est) and detecting cavitation or likelihood of the cavitation of the pump and/or reverse flow of the pump from one or more of the formed features (Feature1, Feature2, Feature3, Feature4).

Claims

1. A method for driving a pump controlled with a frequency converter, wherein the method comprises:

controlling the pump with a frequency converter, the frequency converter feeding a motor connected to drive the pump,

providing a torque estimate (T_est) and/or a rotational speed estimate (n_est) of the motor from the frequency converter,

forming one or more features (Feature1, Feature2, Feature3, Feature4) indicating cavitation or likelihood of cavitation of the pump and/or reverse flow of the pump using the provided estimates (T_est, n_est), and

detecting cavitation or likelihood of cavitation of the pump and/or a reverse flow of the pump from one or more of the formed features (Feature1, Feature2, Feature3, Feature4).

2. A method according to claim 1, wherein an indicating feature (Feature1) is formed by

comparing an RMS value of alternating component of the torque estimate (T_ac,RMS) with the normal RMS value of alternating component of the torque estimate (T_ac,N).

3. A method according to claim 1, wherein an indicating feature (Feature2) is formed by:

comparing an RMS value of alternating component of the rotational speed estimate (n_ac,RMS) with the normal RMS value of alternating component of the rotational speed estimate (n_ac,N).

4. A method according to claim 1, wherein an indicating feature (Feature4) is formed by:

calculating an estimated volumetric flow (Q_est) from direct components of the torque estimate (T_dc,est) and the rotational speed estimate (n_dc,est) using a pump model, and

comparing the estimated volumetric flow (Q_est) with an allowable minimum volumetric flow (Q_min) that is transformed to a present rotational speed.

5. A method according to claim 1, wherein an indicating feature (Feature3) is formed by

calculating net positive suction head required (NPSH_R) from direct components of the torque estimate (T_dc,est) and the rotational speed estimate (n_dc,est) using a pump model,

calculating net positive suction head available (NPSH_A) from system parameters, and

comparing the net positive suction head available (NPSH_A) with the net positive suction head required (NPSH_R).

6. A method according to claim 2, wherein a calculation of the RMS value of alternating component of the torque estimate (T_ac,RMS) and of the rotational speed estimate (n_ac,RMS) comprises:

separating low-frequency alternating components from the torque estimate to obtain separated alternating component values (T_ac;

n_ac), and

calculating RMS value from the separated alternating component values.

7. A method according to claim 1, wherein direct components of the torque and rotational speed estimates are determined by low-pass filtering or by calculating mean values of the torque estimate and rotational speed estimate, respectively.

8. A method according to claim 4, wherein the calculation of estimated volumetric flow (Q_est) comprises:

calculating estimated power consumption (P_est,dc) of the pump from the direct components of the torque estimate (T_dc,est) and rotational speed estimate (n_dc,est), and

determining from given pump parameters the estimated volumetric flow (Q_est) on a basis of the estimated power consumption (P_est,dc).

9. A method according to claim 5, wherein the calculation of net positive suction head required (NPSH_R) comprises:

calculating estimated power consumption (P_est,dc)) of the pump from the direct components of the torque estimate (T_dc,est) and rotational speed estimate (n_dc,est),

determining from given pump parameters an estimated volumetric flow (Q_est) on a basis of the estimated power consumption (P_est,dc), and

determining from the given pump parameters an estimated positive suction head required (NPSH_R) on a basis of the estimated volumetric flow (Q_est).

13. A method according to claim 2, wherein an indicating feature (Feature2) is formed by:

comparing an RMS value of alternating component of the rotational speed estimate (n_ac,RMS) with the normal RMS value of alternating component of the rotational speed estimate (n_ac,N).

14. A method according to claim 3, wherein a calculation of the RMS value of alternating component of the torque estimate (T_ac,RMS) and of the rotational speed estimate (n_ac,RMS) comprises:

separating low-frequency alternating components from the torque estimate to obtain separated alternating component values (T_ac;

n_ac), and

calculating RMS value from the separated alternating component values.

15. Method according to claim 1, wherein the detecting comprises:

detecting cavitation of the pump.

16. Method according to claim 1, wherein the detecting comprises:

detecting cavitation of the reverse flow.

17. Method according to claim 1, wherein the providing comprises:

providing the torque estimate.

18. Method according to claim 1, wherein the providing comprises:

providing the rotational speed estimate.

10. A system for driving a pump controlled with a frequency converter, wherein the system comprises:

a frequency converter for controlling a pump, the frequency converter feeding a motor for driving the pump,

means for providing a torque estimate (T_est) and/or a rotational speed estimate (n_est) of the motor from the frequency converter,

means for forming one or more features (Feature1, Feature2, Feature3, Feature4) indicating cavitation or likelihood of cavitation of the pump and/or reverse flow of the pump using the provided torque and rotational speed estimates (T_est, n_est), and

means for detecting cavitation or likelihood of cavitation of the pump and/or reverse flow of the pump from one or more of the formed features (Feature1, Feature2, Feature3, Feature4).

11. The system according to claim 10, wherein the system is incorporated in the frequency converter.

12. A frequency converter, for feeding a motor used to control a pump, the frequency converter comprising:

means for providing a torque estimate (T_est) and/or a rotational speed estimate (n_est) of the motor from the frequency converter,

means for forming one or more features (Feature1, Feature2, Feature3, Feature4) indicating cavitation or likelihood of cavitation of the pump and/or reverse flow of the pump using the provided torque and rotational speed estimates (T_est, n_est), and

means for detecting cavitation or likelihood of cavitation of the pump and/or reverse flow of the pump from one or more of the formed features (Feature1, Feature2, Feature3, Feature4).