Evaluation of Glass Transition Temperature and Thermal Shock of Impregnating Resins

The selection of an impregnating resin for electrical equipment is critical to its performance and lifetime. Impregnating resins serve a variety of functions including mechanical bonding, additional electrical protection, and environmental protection. The relative importance of each of these often depends on the final application of electrical equipment. For example, mechanical bonding is paramount in random wound commercial motors. The magnet wire windings in these motor stators are subjected to mechanical stress during operation. It is vital that the individual strands of magnet wire are not allowed to rub against each other during operation. The rubbing will eventually result in failure of the insulation.In high voltage machines, the electrical performance of the impregnating resin is critical. During the impregnation process the resin, ideally, penetrates all the layers of mica and in between individual conductors in the coils. The resin has a tremendous impact on the electrical performance of the entire machine since it is an integral part of electrical insulation.Impregnating resin specifiers prioritize a range of properties including liquid and cure properties. The liquid properties influence the impregnation process. There are a variety of cured properties. One property that is often specified is glass transition temperature. Often the glass transition is specified to be above the operating temperature. The theory is that if equipment heats from below the glass transition temperature to above it, the resin will crack. This study will evaluate different resins with varying glass transition temperatures under thermal shock conditions.