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What To Consider When Deciding to Repair NEMA Premium Motors

Is it better to repair or replace an electric motor that fails? For most plant engineers and maintenance staff, experience attests to the reliability of standard efficiency motors that have been repaired or rewound using industry best practices. Repair also can cost far less than replacement, especially if the motor has special features.

But some decision makers opt to replace failed energy efficient motors (NEMA Premium models in particular) because they’ve “heard” these motors can’t be repaired without a loss of efficiency. 

So, what’s the right answer? It turns out that the decision to repair, rewind or replace a failed energy efficient motor is not always so simple and straightforward as you may have heard.

Read the complete article by Tom Bishop, P.E., EASA Senior Technical Support Specialist, at Plant Engineering.

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The Effect of Repair/Rewinding on Motor Efficiency

EASA/AEMT Rewind StudyPublished: December 2008

The Effect of Repair/Rewinding on Motor Efficiency: EASA/AEMT Rewind Study and Good Practice Guide illustrates that when performed properly, electric motor repair/rewind does not degrade efficiency! Nor is motor efficiency reduced through multiple repairs/rewinds.

Based on a joint study by EASA and the Association of Electrical and Mechanical Trades (AEMT) of the United Kingdom, this publication concludes that using best repair/rewind practices maintains motor efficiency. 

Besides an Executive Summary, the report provides complete test data, extensive background information about test procedures and methodology, information about best practice repair/rewind procedures, resources for further reading, and an entire chapter on repair/replace considerations.

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Download the update to this study published in June 2020!

DOWNLOAD THE EXECUTIVE SUMMARY

ANSI/EASA AR100-2020: Recommended Practice for the Repair of Rotating Electrical Apparatus

ANSI/EASA AR100-2020 coverPublished: September 2020

EASA’s “Recommended Practice for the Repair of Rotating Electrical Apparatus” is designated ANSI/EASA AR100 and was first approved as an American National standard in 1998. Since then it has been revised and approved four more times, in 2001, 2006, 2010, 2015 and now in 2020. 

ANSI/EASA AR100 is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.

The scope of this document describes record keeping, tests, analysis and general guidelines for the repair of induction, synchronous and direct current rotating electrical apparatus. It is not intended to take the place of the customer's or the machine manufacturer's specific instructions or specifications or specific accepted and applicable industry standards or recommended practices.

This document should be supplemented by additional requirements applicable to specialized rotating electrical apparatus including, but not limited to, listed explosion-proof, dust-ignition proof, and other listed machines for hazardous locations; and specific or additional requirements for hermetic motors, hydrogen-cooled machines, submersible motors, traction motors, or Clas 1E nuclear service motors.

ANSI recognizes only one standard on a topic; therefore, the EASA Recommended Practice is the standard for repair of rotating electrical apparatus.

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Guidelines for Maintaining Motor Efficiency During Rebuilding

Published: November 2007

This article provides guidelines that service centers can follow to retain the operating efficiency of the electric motors they rewind and rebuild. It includes a list of "do's and don'ts", safe values and correct procedures based on studies of variables that can impact the efficiency of rewound electric motors (core burnout temperature, winding design, bearing type, air gap, winding resistance, etc). 

This article was first published in May 1992; reviewed and revised as necessary in November 2007 by EASA's Technical Services Committee.

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Can you repair energy-efficient motors? Maybe.

An EASA-authored article that appeared on the Canadian Forest Industries website — www.woodbusiness.ca

Most plant engineers and maintenance staff can attest to the reliability of standard-efficiency motors that have been repaired or rewound using industry best practices. They also know repair can cost far less than replacement, especially when the motor has special features. Despite this, some of them hesitate to have failed energy-efficient motors (NEMA Premium models, in particular) repaired because they’ve heard it degrades efficiency.

So, what’s the right answer? Is the decision to repair, rewind or replace a failed energy-efficient motor as simple and straightforward as you may have heard?

Topics in the article include:

  • What makes a motor more energy-efficient?
  • Repaired motor efficiency
  • Review the motor application
  • Catastrophic failure (present)
  • Catastrophic failure (prior)
  • Rotor condition
  • Mechanical parts condition
  • Higher-efficiency motors

READ THE FULL ARTICLE