Electric Field Distribution at High Temperatures in Impregnated Enameled Conductors used in Electrical Machines

The partial discharge inception voltage (PDIV) is a critical parameter for the reliability of electrical machines incorporating SiC and GaN converter technologies. Most of the machine impregnation resins operate in the plasto-viscous region (above their glass-transition temperature) where large permittivity values can be expected. At high temperature field enhancement in the air surrounding such materials may be expected, potentially reducing the PDIV. In this study, two different epoxy-based impregnation resins with significant differences in contribution to PDIV performance have been compared. For both strong correlation is found among impregnated twisted pairs sample capacitance and flat resin sample permittivity as function of temperature. Simulations of the electric field distribution suggest that PDIV depends mostly on the coating properties of the resin rather than its dielectric one and that a good resin overcoating layer thickness or a buildup of resin in-between the wires are needed to improve the performances.