Chuck Yung
EASA Senior Technical Support Specialist
Redesigning electric motors has become commonplace for motor repair service centers. By changing one or more motor characteristics, service centers often can adapt motors to meet new requirements faster and more economically than they can obtain new ones.
This paper explains how to make any changes in the ratings of AC electric motors that are possible within design limitations. Examples of each redesign are included as a guide for making your own redesigns. Besides mathematical formulas, this section provides guidelines on the limitations for each type of redesign. These guidelines will also help you determine whether a desired new rating is possible before you strip a motor.
In most service centers, there are rules regarding what winding changes can be made, who can make them, and who must approve them. Make sure that redesigns are not made without going through the proper channels.
This paper gives a brief review of AC motor theory and operation that includes flux pattern, types of losses, NEMA design designations and test procedures. It also covers:
- Design considerations for slip-ring and synchronous motors
- Requirements for reduced starting voltage
- Formulas for redesigning polyphase and single-phase AC equipment.
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