Method and system for detecting cavitation of pump and frequency converter

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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ) 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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ).

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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ) 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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ).   
   
   
       2 . A method according to  claim 1 , wherein an indicating feature (Feature 1 ) 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 (Feature 2 ) 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 (Feature 4 ) 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 (Feature 3 ) 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 ).   
   
   
       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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ) 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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ).   
   
   
       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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ) 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 (Feature 1 , Feature 2 , Feature 3 , Feature 4 ).   
   
   
       13 . A method according to  claim 2 , wherein an indicating feature (Feature 2 ) 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.