Reduction of Measurement Fluctuation of Partial Discharge Inception Voltage for Inverter-fed Rectangular Wire Motors

In this research, we investigated the factors which affect PDIV fluctuation between the coil wires under a sinusoidal voltage by using a rectangular wire motor (AIW coating, thickness 40µm) in which the neutral point is unconnected. Experimental results revealed that PDIV under low humidity environment fluctuated at the initial period of pre-discharge, whereas PDIV under high humidity environment increased transiently after the pre-discharge. Furthermore, the PDIV transition under high humidity environment decreased at high measuring frequency, which is not influenced by the absorbed moisture in the coating. To clarify their mechanisms, we performed surface charge measurement and electric field analysis taking account of the change in surface conductivity of coating with a water adhesion.…