Motor Efficiency of Rewound Motor

[jerf]

How much motor efficiency is likely to be lost when a burned out moptor is rewound? The motor in question is the motor of a submersible sewage pump rated at 440 litres/sec at 45 metres head - motor power P1 = 267 kW P2 = 250 kW

 

[Artisi]

If the motor was rewound to spec. what makes you think that there will be any loss of efficiency.

International College
Naresuan University
Phitsanulok
Thailand

 

[electricpete]

You mention burn out which means you are aware of the biggest hazard: if the stator is placed in an oven to facilitate removal of the old windings and temperature is not controlled within the proper range, the stator interlaminar insulation will be damaged.

Our specification includes the following items:
Limit over burnout temperature below 650F.
Provide continuous record of burnout oven temperature to demonstrate the above requirement was met.
Perform core loss test prior to winding removal (85,000lpsi).
Perform core loss test after winding removal (85,000lpsi).
A 5% increase in core loss (watts/pound) before=> after indicates substantial core degradation and must be addressed.
Some people limit core loss to around 4 watts per pound.

If core loss increases by 10% you can figure original core loss was approx 25% of total losses. Total losses increase by 2.5% of their original value. If total losses were 10%, then efficiency decrease from for example 90.0% to 89.75%.

EASA has published some studies on the subject which may be available for free. Another factor I remember is damage to the teeth of semi-closed stator slots which disrupts the flux pattern and increases losses.

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[electricpete]

Here are results of a study on this subject, available on-line for free:

http://www.easa.com/indus/rwstdy1203.pdf

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[electricpete]

I forgot to warn that this is a 1 Megabyte file, so easier to download to your hard-drive to view.

Also, to get to the EASA documents available for free
download:

Go to

http://www.easa.com

Click on industry info

The file I have linked is labeled "The Effect of Repair/Rewinding on Motor Efficiency"

Another file of interest is labeled "Guidelines for Maintaining Motor Efficiency During Rebuilding"


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[jerf]

To ElecticPete,

Thankyou for those references, they are very helpful, and although they do not make mention of metric motors - the prinicpals will be the same, and problems of bad maintenance the same!

I did download to view that was much easier!

Regards

John Fulton