Space Charge Distribution Measurements of Thin-Film Insulating Materials with Slow Sound Velocity using a High-Resolution PEA System

Partial discharge (PD) associated with higher voltages in inverter-driven motors has become a problem; one of the reduction causes of PD-inception voltage is said to be the space charge that accumulates in the winding coating material, especially at high temperatures, and it is necessary to investigate this accumulation characteristic. However, the typical thickness of the coating material of the windings used in electric vehicles is about 30 μm, making it difficult to measure the space charge distribution with the usual PEA (pulse electrostatic stress) method, which has a positional resolution of about 10 μm. In the present study, a thin P(VDF-TrFE) piezoelectric sensor was formed directly onto a ground electrode deposited on both sides of sapphire glass, which is said to have good acoustic propagation characteristics, by the spin coating method, and used to obtain a position resolution of about 2.5 μm at
$80^{\mathrm{o}}\mathrm{C}$
. The resolution was successfully improved significantly.