Behavior of a Machine Insulation System during Accelerated Aging Tests

The contribution presents results from extensive investigations on the behavior of a VPI machine test insulation system (thermal class F (155degC)), which was subjected to a thermal overstress (175degC) in repeated cycles. It will represent the thermal deteriorating effects of an insulation system in service on an accelerated basis. After each thermal cycle the insulation system is subjected to mechanical stress, moisture, and voltage. In order to check the condition of the insulation systems in a non-destructive manner several properties of insulation like dissipation factor, capacitance, insulating resistance and partial discharge quantities were measured after each thermal cycle. The results indicate how the changes in electrical and dielectric properties of insulation take place during the accelerated aging test.