The Influence of corona discharge on space charge accumulation in polyimide film

The space charge accumulation processes in polyimide film under corona discharge from spherical electrode are observed using improved open-electrode type PEA (pulsed electro-acoustic) measurement system. To reduce the electric power consumption, the efficient-energy motor is required to be developed. One of effective improvement of the efficiency of motors is to increase the driving voltage for it. However, if the driving voltage is increased, a large, so called “inverter serge voltage” is applied to the coating insulating material for the motor windings, then partial discharge (PD) occurs between the wires or the wire and the grounded metal of the motor. The partial discharge gives serious damages to the insulating material and it leads the breakdown finally in the insulating material. Therefore, it is important to understand the mechanism of the generation of partial discharge. Especially, the space charge formed in the insulating material under such condition is supposed to affect the generation of the partial discharge. However the relationship between the space charge and the PD haven't been cleared yet. Therefore, we have tried to measure the space charge accumulation in the material under corona discharge using PEA system. In this report, some typical results of space charge profiles measured after surface discharge are introduced. As the results, we have found that the space charge formation in polyimide film under corona discharge is easy to accumulate.