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The importance, benefits of preheating motor windings prior to impregnation

  • May 2002
  • Number of views: 307
  • Article rating: No rating

Tom Bishop
EASA Technical Support Specialist 

Did you ever wonder if the preheating instruc­tions from solvent varnish and solventless resin (hereafter we’ll use the term “resin” when it ap­plies to both) manufacturers were really all that important? The short answer is, yes, they are. Here we’ll expand on some of the reasons that preheating is a key step in the winding process. 

One of the first benefits of preheating is that it drives out moisture that may have settled on sur­faces, or been absorbed by insulation material. A little known aspect of pre­heating is that it relieves the mechanical stress cracks, termed “crazing,” on the magnet wire insulation coat­ing that occur during coil winding and insertion. Epoxy B-stage materials can be set by preheating, provided the preheating time and tempera­ture meet the epoxy’s curing requirements. Random wind­ings typically don’t use many B-stage materials; however, many of the lacing products for endturns are thermoset­ting. Form coil windings often have B-stage surge ropes, and some felt packings used for endturn coil bracing are B-stage epoxy loaded. 

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Getting The Most From Your Electric Motors

Getting The Most From Your Electric Motors - coverThis 40-page booklet provides a great marketing tool for your service center! Use it to provide end users with information that will help them obtain the longest, most efficient and cost-effective operation from general and definite purpose electric motors.

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EASA Technical Manual

EASA Technical Manual cover

The EASA Technical Manual is the association's definitive and most complete publication. It's available FREE to members in an online format. Members can also download PDFs of the entire manual or individual sections.

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ANSI/EASA AR100-2015

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Recommended Practice for the Repair of Rotating Electrical Apparatus
This 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.

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EASA AR200

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Guide for the Repair of Power and Distribution Transformers
This document establishes guidelines for each step of the repair of power transformers, describing record keeping, tests, analysis, and general guidelines for the repair of power transformers.

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