Contents I. Introduction
In recent years, semiconductor power devices have a technology trend for higher voltage and operating frequencies, and highly efficient operation. Although an inverter can efficiently change the speed ofa motor, it is a problem that surge voltage caused by high-speed switching ofthe power devices is superimposed on the motor terminal. This overvoltage to the drive voltage is usually called an inverter surge. When such an inverter surge enters a motor terminal, partial discharge (PD) might occur at the wedge gap between the enamel windings. As a result, the insulation coating ofthe winding may Ue damaged. As a method of suppressing PD, it is effective to decrease the voltage across the wedge gap by reducing the relative permittivity of the insulating film of the winding. From the viewpoints, the authors have developed a micro cellular film with lower relative permittivity than the conventional insulating film. The partial discharge inception voltage (PDIV) of the twisted pair wire with the cellular coating and PDIV[breakdown voltage of the cellular film have been verified [1] – [4] . In order to theoretically verify PDIV of cellular coating twisted pair under impulse voltage, this paper deals with PDIV evaluation and discussion using Volume-Time theory [5] – [8] which provides PDIV estimation under various voltage waveforms in air and S F6 gas.
