Insulation systems are designed to take maximum advantage ofmaterial technology and it is important therefore to be able to defineboth the electrical and mechanical limits of any new system. Theintroduction of variable speed drives have thrown even greater stressesupon insulation materials and the ability to be able to predict lifetimes under these new conditions is now a vital part of the insulationsystem evaluation. In addition to a gradual increase in the thermalrating of materials there has been another change, albeit less obvious,in the way in which machines are operated. In the ever more costeffective and efficiency driven world in which we now find ourselves, itis increasingly common to find both motors and generators runningcontinuously for several years without a shutdown. This, therefore,requires thorough evaluation of both electrical and mechanical stresseswhich are to be imposed on the winding. The author discusses electricalstress, mechanical stress, and impregnation in relation to machineinsulation materials development
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