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IEEE 434 2006 Edition, December 6, 2006
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Guide for Functional Evaluation of Insulation Systems for AC Electric Machines Rated 2300 V and Above
Includes all amendments and changes through Reaffirmation Notice , February 6, 2013
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This guide describes a procedure that may be used to evaluate and compare insulation systems used, or proposed for use, in large ac electric machines.

The tests outlined herein are applicable to the groundwall insulation systems applied to form-wound, preinsulated armature (stator) winding coils and/or bars of generators, motors, and synchronous condensers rated 2300 V or higher.

The basic component of these insulation systems is usually mica combined with reinforcing, bonding, and impregnating materials.This guide is based on the experience of the industry with mica-based systems; any evaluation of other insulation systems should, however, consider the recommendations of this guide.

This guide is not intended for use as a manufacturer's quality assurance test plan. Nor should it be used for specifying or procuring armature winding coils/bars.


During operation, an insulation system is subjected to electrical, thermal, mechanical, and environmental stresses that act and interact to cause irreversible changes in the properties of the insulation. The applied stresses initiate aging mechanisms that eventually lead to failure. The purpose of this guide is to provide a means of evaluation in which groundwall insulation systems, as described in 1.1, are exposed to influencing factors that simulate or are characteristic of actual service conditions. This guide establishes the basis for evaluating the aging of the electrical insulation system as a result of these influences.