Analysis of the critical stresses in high-voltage composite winding insulations under thermal loads

Stator bars are the critical components in generators with respect to their lifespan. The winding insulation may be susceptible to damage under excessive alternating temperature loads incurred by a high number of start–stop cycles and heavy overloads. The differences in thermal expansion between the different components in the multi-layered winding insulation lead to thermal stresses. This work deals with the thermo-mechanical characterisation of the individual constituents of the winding insulation and the finite element model of a stator bar, based on the material data obtained from the tests that enable the identification of the thermal stresses leading to delamination over thermal cycles. The out-of-plane and the interfacial shear stress are found to be in the critical range with respect to the relatively low cohesive strength of the included individual mica layers.