Partial discharge inception voltage of enamel twisted-pair samples with several laminated insulation layers

It is needed for the insulation system of inverter-fed motors used for industrial motors and electric vehicle to have high partial discharge inception voltage (PDIV). In this paper PDIV test was performed on twisted pair specimens of enameled wires consisting of polyamide-imide resin and polyester-imide resin alternately-layered. PDIV characteristics of the twisted pair specimens were measured by applying AC voltage at 60Hz and bipolar repetitive impulse voltage simulating inverter surge that appears in inverter-fed motor insulation system. The repetitive impulse voltage, the rise time, pulse width, repetition frequency, and rise rate of voltage of the repetitive voltage impulse were 200 ns, 1 ms, 500 Hz, and 500 V/min, respectively. For ac voltage at 60 Hz. The rise rate of ac voltage was 15 V/s. Twelve experiments for ac test were made with an interval of 10 s. The PDIV was also estimated using electric field analysis for the twisted pair on the basis of Paschen's law to the air gap formed between the two enamel wires. We fabricate enamel wire with the different permittivity materials alternately-layered. It was found that PDIV of the sample with the lower permittivity material as a single layer is larger than that with the higher permittivity one. On the other hand, it was also found that PDIV of the sample with the layered insulation almost does not change.