Charge vibration behaviour in polyimide under the pulse voltage with different rise and fall times

Abstract High‐voltage electronic equipment is widely used in power systems, which normally operate under the pulse voltage condition. However, compared to DC or AC stress, the electrical insulation suffers a more severe ageing process under a pulse voltage with steep edges and so may cause electrical equipments to fail early. The charge behaviour in polyimide under the pulse voltage with different edge times was investigated in this study. The experimental results show that charges vibrate at the pulse edge, while the amplitude of charge vibration increases with decreasing edge times. Furthermore, the detected vibration signal is strong within the nanosecond edge times, while being negligible in the microsecond range. Notably, the amplitude of charge vibration at the falling edge is larger than that at the rising edge in the presence of the column‐plate electrode. It is believed that the resultant force acting on the charge increases drastically at the pulse edges, leading to the charge movement and the generation of ultrasonic waves, with the resultant force becoming larger when the edge times decrease. Charge vibration behaviour is harmful to the microstructure of insulation materials, and so it may be concluded that the rise and fall times of the pulse voltage play an important role in insulation failure.