Comparative PDIV and endurance studies on different insulating materials used for medium frequency transformers

Medium frequency transformers in the power electronic system suffer from unusual electrical stress. With short rise time and higher frequency of the PWM voltage, interturn/layer overvoltage and overheating can be induced in the transformer's winding. Partial discharge may be triggered with higher probability and may lead to premature failure of the insulation. Therefore, it is necessary to improve the insulation capability of medium frequency transformers with respect to resisting partial discharge generation and deterioration under PWM-like voltage and high temperature. To achieve this goal, selection of better insulation material is critical. This paper presents comparative partial discharge inception voltage and endurance lifetime studies on three different materials including polyimide, polyester and Nomex paper, which are usually used for the insulation of medium frequency transformers. Results show that polyimide and polyester behave better than Nomex paper in resisting partial discharge inception. While polyimide shows longest endurance against continuous partial discharge.