Aging properties of polyimide materials under square impulse voltage

In order to investigate the inter-turn insulation of frequency-variable motor, using the electro-thermal method, we aged 100HN twisted cable pairs and 100CR twisted cable pairs with square impulse voltage, and measured their dielectric loss characteristics and partial discharge(PD) parameters during different aging stages. The results show that, for both of the cable pairs, 100HN and 100CR, their dielectric loss, mean PD quantity, and PD numbers increase with the aging time. However, there are inter-facial regions with a lot of shallow traps around the nanoparticles in 100CR, which raises the capacity of charge transport. Therefore, compared with 100HN under the same aging conditions, 100CR has larger dielectric loss and PD number but smaller mean PD quantity. Moreover, the synergistic effect of nanoparticles helps to protect the polyimide matrix in 100CR, and hence can extend the insulation lifetime of 100CR.