Should Electric Motors be Rewound?
Updated: Aug 25, 2022
Updated: January 15, 2021,
(Click for more...) There’s a long-held belief that rewinding a motor causes a loss in efficiency and reliability. Thanks to EASA’s 2003 study “The Effect of Repair/Rewinding on Motor Efficiency”, we learn that, IF DONE CORRECTLY, rewound motors do NOT lose efficiency even after multiple rewinds.
After reading and thinking about the 2003 EASA study, two things popped into my head:
1. Electric motors CAN be rewound without an efficiency or reliability loss.
2. The long-held belief that efficiency and reliability loss—CAN BE TRUE, if poor lamination winding removal methods are used.
The 2003 study, on page 1-15, (section titled) “Stray Loss analysis” indicates an average .4% (or nearly a half of 1%) loss in efficiency. The loss was due to splayed (or bent) lamination teeth in Group A (see page 1-18 Table 9), efficiency losses in this Group were caused by magnetic pulsating or a zig-zag effect between separated lamination teeth increasing stray losses.
The following are a few thoughts:
1. My local newspaper, the Idaho Statesman, reported that a “1% change in efficiency at 200 HP, is enough energy to power the average American home.”
2. The energy losses from EASA’s 2003 study Group 1, were about a half of one percent due to splayed (bent and separated) teeth, and likely manifests itself as heat, near bearings and lubrication.
3. Over 50% of motor failures are bearing related.
4. Efficiency and reliability are often interconnected, particularly in “T” frame motors.
5. Rule Number One of motor repair is to protect (do NOT damage) components to be reused, including laminations.
The motors in the rest of the 2003 study, were carefully stripped without splaying lamination teeth, thereby retaining original as manufactured efficiency—Even after MULTIPLE rewinds!
From EASA’s 2003 study and what I see during my many EASA Accreditation and Green Motor Initiative audit visits—Our industry needs to pay more attention to not bending or splaying teeth during lamination wire removal.
Addendum December 2020
EASA conducted and published a follow-up titled, “The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors”. Which is specific to Premium Efficient/IE3 Motors—In-essence, adds currently available premium efficient motors to the original 2003 rewind study.
As a side note, EASA’s Accreditation Program and the Green Motor Initiative dovetail these studies, along with ANSI/EASA AR100-2020, into motor service center’s shop processes with specific controls on stripping, rewinding, and mechanical repair to retain three-phase motor efficiency and reliability. We hear more and more that end-users and motor warranty repairing for manufacturer's, have added motor service center EASA Accreditation to their motor repair specifications.
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