Influence of pressure on the PD and induced aging behavior of polyimide insulation under repetitive pulse voltage

Reduction of air pressure can influence insulation material’s behavior with respect to resisting partial discharge (PD) generation and its induced aging process. This may bring threat to the insulation reliability of medium frequency transformers working under low pressure condition, considering they are exposed to high probability of PD inception caused by pulse width modulation (PWM) voltage. Aiming at investigating the performance of insulation of medium frequency transformer being operated in an environment with a decreasing pressure, this article introduces a test system that can conduct PD and endurance lifetime tests under repetitive pulse voltage and controlled pressure. Using this test system and focusing on polyimide film, which is one of the main insulation materials used by medium frequency transformers, PD and endurance lifetime tests are conducted under different pressures. The results show that PD inception voltage decreases with decreasing pressure. However, the changing of PD magnitude, time lag and its induced insulation lifetime do not change monotonously. Surface of the failed insulation samples show that the erosion area caused by PD is larger under lower pressure. The mechanisms behind the changing of PD time lag, discharge magnitude, endurance lifetime, along with the discharge eroded area with pressure are discussed in detail.