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#1 jamco23

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Posted 25 September 2005 - 08:01 PM

Perhaps this has been asked before ?

Does fitting a VSD to a pumping well reduce the running costs for a 3 phase induction motor,both in maintenance, life time costs and electricity, instead of just a DOL / star-delta

I personnally can't see how it can, comments please

#2 marke

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Posted 25 September 2005 - 08:50 PM

Hello jamco23

Welcome to the forum.

Fitting a VSD to a pump can save money but not in every situation.

If the pump is operating at full speed and full flow, there will be no gain from adding a VSD.
If the pump is operating at full speed and reduced flow, there can be losses in the pump which can be reduced by slowing the pump down.
Slowing the pump down so that it operates on the most efficient part of the curve can yeild sufficient energy saving to overcome the additional losses in the drive and yeild a net energy gain or money saving.

In other words, if the flow is constant, and the pump is correctly sized for that flow, there wil be no improvment in the pump efficiency and there will be additional losses due to the VSD.
If the flow is not constant, (on demand) or the pump is well over sized, there will be an improvment by slowing the pump down. The pump would normally be operated using a pressure transducer and PID loop to maintain a constant head.

Best regards,

#3 msdaif

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Posted 26 September 2005 - 12:49 PM

DOL or Star/Delta starters are good for small pumps which are usually
used in factories and perhaps farms. So it is stupid to install VSD's.

Very huge pumps employed, for instance, in big city water supply and sewage systems are driven by VSD's.

#4 marke

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Posted 26 September 2005 - 07:09 PM

msdaif

While the DOL starter is able to be used on small pumps, it is only one option. There can be significant advantages in using soft starters or vsds on these applications. If there is a supply issue, or water hammer problem, the soft starter can provide a significant improvment over the DOL starter (at a cost). If the flow is variable, there can be an energy saving by the use of a VSD, or if the line is very presure sensitive, the VSD can be used to limit the line pressure.

Large pumps are commonly controlled by either soft starters or VSDs depending on the requirements.

Best regards,

#5 oskin

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Posted 27 September 2005 - 12:43 AM

I agree with the use of softstarters over DOL or even Star delta starting of Centrifugal pumps. Apart from the obvious electrical advantages the mechanical strain on the spline or shaft can be greatly reduced.
Most impellors are keyed onto the shaft and the effects of inertia on start up can be clearly seen on older pumps with wear on the shaft and the impellors getting sloppy.So I guess that the short answer is, yes, it would improve life time and maintenance costs.




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