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why motor of centrifugal pump has low efficiency

why motor of centrifugal pump has low efficiency

why motor of centrifugal pump has low efficiency

(OP)
I am just wondering why always we found that in centrifugal pump, its motor efficiency is very low (sometimes around 40%)?

Mohd Yaseen

RE: why motor of centrifugal pump has low efficiency

How did you decide on that figure?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: why motor of centrifugal pump has low efficiency

Do you really mean "motor" or the whole pump set (electrical power in versus hydraulic power out)??

If it is whole pump set then you're either working well outside the best efficiency or you're using small low efficiency pumps.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: why motor of centrifugal pump has low efficiency

(OP)
Artisi
I have tentatively set that figure base on my experiences (pumps that pass through my work)


LittleInch

I mean the motor efficiency (power transmitted to the pump shaft / input power from power system)

I have no doubt about the centrifugal pump efficiency which ranging above than 70% in most cases I have ever seen.

Mohd Yaseen

RE: why motor of centrifugal pump has low efficiency

well without any more data (line voltage, phases, power in, measured shaft power out (how measure?) motor sizes etc there's no real way to answer this.

Most reasonable size motors >10kW motors I've come across have efficiencies > 95%.

What does the motor data sheet say?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: why motor of centrifugal pump has low efficiency

Well, if the motor is operating at very low load (small fraction of rated load), it might have that low efficiency for motor itself.

I agree with Artisi and LittleInch that you need to be more specific about what you're talking about. Give an example machine and describe associated measurements or documents that led you to this conclusion.

=====================================
(2B)+(2B)' ?

RE: why motor of centrifugal pump has low efficiency

Show up a print with the type of pump and family of pump curve....

Some types of pumps with large solids passing capabilities (sewage pumps) or self-priming pumps have low efficeincies due to the nature of their design.

Most squirrel cage AC motors operate with high efficiency ....

MJCronin
Sr. Process Engineer

RE: why motor of centrifugal pump has low efficiency

Howdy Mohd Yaseen,
I agree 100% with LittleInch. I am used to seeing FL (& 75% FL) efficiencies of up to 96% for larger motors.
There is no way that an electric motor can have a FL efficiency of 40%.
Please provide a typical motor datasheet.
Curious,
GG

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

RE: why motor of centrifugal pump has low efficiency

If you're using the measured clamp-on amps times the voltage you will not be seeing anything close to the actual 'power' the motor is consuming. A bunch of the current that measures is not doing "work" in the strict definition of energy and power. You are not paying for that reactive current (directly anyway). That's is a common error.



Keith Cress
kcress - http://www.flaminsystems.com

RE: why motor of centrifugal pump has low efficiency

You should get a better amp reading from the ammeter dedicated to this motor at the starter cubicle in the control room-MCC.

RE: why motor of centrifugal pump has low efficiency

But, again that shows all the current including the magnetizing current. That is what's flowing thru the cables and what the breakers and wiring should support but only part of that current contributes to power consumption. The percentage is greatly affected by the motor load and the voltage. You need to have a kwHr meter or specifically a power meter to make any comment what-so-ever about a motor's efficiency. An ammeter is useless.

Keith Cress
kcress - http://www.flaminsystems.com

RE: why motor of centrifugal pump has low efficiency

Mohd,

Contrary to what you posted above
"I mean the motor efficiency (power transmitted to the pump shaft / input power from power system)
I have no doubt about the centrifugal pump efficiency which ranging above than 70% in most cases I have ever seen. "

What you posted was the pump data sheet and pump curve NOT the motor data sheet or its power to efficiency curve.

So yes, your pump is low in efficiency ( max 49%) - poor design or operating at the end of where it likes to be - that's down to the pump designer, nothing to do with the motor.

At that sort of size of pump I would expect somewhere up from 60% as the Best efficiency.

However it was probably cheaper than a more efficient pump and someone who only cared about CAPEX made the decision with probably no thought or influence about the OPEX costs or cost of power supplies / cables / switchboards etc.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: why motor of centrifugal pump has low efficiency

(OP)
Dear LittleInch

Thanks for your comprehensive response;

You are right, I confused between the pump & its motor efficiencies. Sorry for misleading all the participants.

Regarding the poorness of the pump efficiency, you revert that to the poorness of the design or its operating at the end of where it likes to be? would you please elaborate me more about this statement cause the pump manufacturer is very good & the pump price is high.

Mohd Yaseen

RE: why motor of centrifugal pump has low efficiency

Mohd,

I'm not a pump guru so can't really comment on what makes one pump more efficient than another, but it will revolve around the impellor design. Pump vendors make pumps that cover a certain range of flow and head. If your requirement falls into that zone then you probably get better efficiency, but if it is at the edge or outside then maybe not.

MJC and artisi may know more.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: why motor of centrifugal pump has low efficiency

Mohd,

Like LittleInch I can't really comment on why that pump's efficiency is so low. Considering it's an API 610 pump from 2012 (not some random, old pump) its very low indeed.

https://www.gouldspumps.com/ittgp/medialibrary/gou...

For example, here is a brochure for a API 610 pump from Goulds. On page 8 they show a family of curves, with several being in the ballpark of your existing pump. Their note says all the curves shown are no less than 80% the BEP (best efficiency point). While the brochure doesn't call it out, I guarantee the BEP of those pumps is greater than 50%.

RE: why motor of centrifugal pump has low efficiency

Mohd, not surprised the efficiency is around 50% as it's a low flow high head multi-stage pump unit and typical /normal for this flow and head. The passage ways thru' the impeller will be very small in area which is subject to friction losses, flow eddies etc and probably with other than the ideal surface finish you can expect and get on larger impellers, all of which reduce hydraulic efficiency.

However, look at it this way, as it goes the job well for you by achieving the flow and head you want, it therefore gets 10 /10 marks - - in my books 10/10 = 100%

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: why motor of centrifugal pump has low efficiency

(OP)
Dear Artisi , thanks for your valuable feedback.

Mohd Yaseen

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