Partial discharge characteristics of twisted enameled magnet wires for inverter-fed random wound motors

Partial discharge (PD) characteristics of twisted enameled magnet wires simulated for random wound motor windings have been investigated. In a voltage endurance test, breakdown positions of the twisted pairs localized at edge parts of the twisted pairs. The localization of the breakdown positions of the twisted pairs disappeared when increasing the applied voltage. It was found that the localization of the breakdown positions originated from inhomogeneous distribution of the PDs at the twisted pairs. An insulating varnish treatment for the edge parts of twisted pairs can prevent the localization of the breakdown positions. As the results, the lifetime of the twisted pairs with the insulating varnish treatment for the edge parts was two times larger than that of the normal ones. Thus, an insulating varnish treatment for edge parts of twisted pairs is desired for a voltage endurance test.