Unravelling High Temperature Induced Glass Transition Effect on Underlying Multi-timescales Dynamic Mechanisms of Epoxy Resin Insulation in Power Electronics Applications

Epoxy (EP) resins find widespread application in power electronics (PE) applications characterized by multi-frequency electrical stresses. Transient thermal overloads are also not uncommon due to, for example, short circuits in the external circuit. This article investigates the influence of various temperatures on broadband dielectric properties of EP insulation, above and below the glass transition temperature (Tg). The underlying multi-timescale dynamic processes, conductivity and relaxation mechanisms are revealed based on multiple spectroscopy techniques. In particular, the dependence on the frequency and amplitude of loss peaks on temperatures is modeled considering the potential use of this model in the multi-physics design of PE applications. Results show that the high temperature above Tg substantially triggers noticeable low-frequency quasi-DC conductance behavior and multiple non-Debye relaxation processes in higher-frequency regions. Once the operating temperature exceeds the Tg, the low-frequency (0.1 to 100 Hz) real permittivity and loss factor will increase by more than dozens of times. The low-frequency quasi-DC conductivity will increase by about 6 magnitudes from 25 ℃ to 200 ℃. As a result of the findings in this paper, the future insulation circuit modeling and reliable insulation design will consider the underlying multi-timescale physical mechanisms to support the multi-frequency applications.