10 replies to this topic

[panagiotis]

Hello everyone,

I have a variable spèed pump and different pump curves for different frequences. Can my operating point be between two curves or it should be exacly on tbe curve?

Thank you in advance!

[breizh]

HI,

Yes ,of course. Affinity laws.

Breizh 

Attached Files

•  Variable_Speed_Pumping.pdf   1.54MB   11 downloads

[panagiotis]

Yes exactly! So my existing pump can operate at a "between" frequency!

[panagiotis]

One further clarification to be sure:
If we assume a VSD pump with 5 different curves for 5 different frequences (800, 900, 1000, 1100 and 1200). Then the pump can operate in a middle frequence e.g between 900 and 1000 Hz, etc. ?

[breizh]

Hi,

What do you mean by 800 to 1200 Hz? where do you get these figures?

Instead of using a Control valve the VSD will adjust the frequency to the flowrate based on signal coming from the flow meter.

 

https://www.linkedin...ps-mark-nellist

 

 

Breizh 

[panagiotis]

Hi Breizh,

 

Thanks for the further information. Please see the attached below to understand what I mean.

This is an existing VSD pump and the calculated point is between the two curves for the two different frequencies.

 

Attached Files

•  VSD.jpg   60.54KB   1 downloads

[breizh]

Hi,

I've no question about what you mean except the data shared in a previous post (800 to 1200 Hz) which worried me. So far, no explanation!  

 

Now regarding your picture, pay attention to the low HZ value and the risk to "burn" your motor if the RPM is not enough for the fan to cool the motor. Probably good for you to talk to an electrician within your organization about VSD best operating condition.

Good luck.

Breizh 

[panagiotis]

Thanks Breizh for the reply. I lost you a bit in your last message!!

[latexman]

Electric motors usually have fan blades attached to the shaft on the opposite side that drives the pump. This is to cool the electrical components that drive the motor. When a VFD slows the motor it also slows the fan which cools the motor, because they are on the same shaft. Most VFDs are set up for constant torque. To do this they increase voltage when they reduce frequency. At some low speed, the motor creates more heat than the fan can remove, and the motor “burns out”, but usually trips its thermal protection circuit.

[breizh]

Hi,

In other words, 30 Hz should be the minimum frequency to operate the pump.

 

Breizh 

[panagiotis]

Thank you so much for the very informative answers, latexman and Breizh.