Motor Efficiency of Rewound Motor
Motor Efficiency of Rewound Motor
(OP)
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





RE: Motor Efficiency of Rewound Motor
International College
Naresuan University
Phitsanulok
Thailand
RE: Motor Efficiency of Rewound Motor
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.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Motor Efficiency of Rewound Motor
http://www.easa.com/indus/rwstdy1203.pdf
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Motor Efficiency of Rewound Motor
Also, to get to the EASA documents available for free
download:
Go to 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"
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Motor Efficiency of Rewound Motor
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