The development of modern high voltage insulation systems for large motors and generators

Insulation systems are designed to take maximum advantage of material technology and it is important therefore to be able to define both the electrical and mechanical limits of any new system. The introduction of variable speed drives have thrown even greater stresses upon insulation materials and the ability to be able to predict life times under these new conditions is now a vital part of the insulation system evaluation. In addition to a gradual increase in the thermal rating of materials there has been another change, albeit less obvious, in the way in which machines are operated. In the ever more cost effective and efficiency driven world in which we now find ourselves, it is increasingly common to find both motors and generators running continuously for several years without a shutdown. This, therefore, requires thorough evaluation of both electrical and mechanical stresses which are to be imposed on the winding. The author discusses electrical stress, mechanical stress, and impregnation in relation to machine insulation materials development