Considerations on partial discharge of nanocomposite enameled magnet wires for inverter fed random wound motors

Nanocomposite enameled wires have been developed for inverter-fed random wound motor windings, however, partial discharge (PD) characteristics is still underlying physics. In this study, effects of environmental conditions on PD characteristics in twisted pairs with conventional and nanocomposite enameled magnet wires were investigated. Measurements of the PD inception voltage (PDIV) and an amount of the PD charge were performed by applying an ac sinusoidal waveform voltage of 60 Hz to the twisted pair. The observed PDIV in this study can be classified into the following three behaviors. First, the PDIV in both wires decreases with increasing relative humidity (RH) at low temperature. Secondly, the PDIV in both wires slightly increases when increasing the RH at high temperature. Thirdly, the PDIV in the conventional enameled wire significantly decreases at 95%RH, while the decrease rate of that in the nanocomposite enameled wire is relatively small. The observed PD phenomena are discussed in terms of material characterization of the enameled wires such as changes in permittivity due to moisture absorption and wettability under voltage application.