Measurement of space charge distribution in polyamide-imide film under square wave voltage practical environment for inverter-fed motor

In the automotive industry, a reduction in CO
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and low fuel consumption are required from the environmental point of view. According to such demand, electric vehicle using an inverter fed motor is developed and widely used. However, partial discharge generates in motor winding, when the higher voltage is applied to the windings. Thereby, it may induce a fatal breakdown in the insulating coating layer of the windings. Judging from a published report, it was said that a decrease of partial discharge inception voltage (PDIV) was strongly related with space charge accumulation in the insulating layer. However, only few studies about the space charge accumulation characteristic in the insulating coating for the windings has been carried out in the past. In this study, we proposed a new space charge distribution measurement technique using Pulsed Electro Acoustic (PEA) method to evaluate the space charge accumulation characteristics in such layer. Using this technique, we can observe the pace charge distribution in an insulating film during the application of square wave, square wave with surge shape and half-wave of AC voltages of 50 Hz to the film. Judging from the obtained results, we found that the space charge accumulated in the film by applying above mentioned the voltages, and it might cause of the reduction of PDIV.