Phase-field modeling of electric-thermal breakdown in polymers under alternating voltage

In this work, a phase-field model is presented to characterize the breakdown properties of polymers under alternating voltage. The breakdown status is described with a spatially and time dependent continuous variable, and the evolution of damage phase is driven by the electrostatic and thermal energy in the system. The relationship between breakdown strength and material properties such as permittivity and dielectric loss can be represented with the phase-field model. For thermoplastic polyolefin with low permittivity and dielectric loss, the electric breakdown is probably the dominant mechanism at room temperature. For other polymers, the breakdown characteristics may be dominated by the electrothermal mechanism. The dielectric loss of polymers increases with temperature, which intensifies the thermal energy and further reduces the breakdown strength. Dielectric loss of polymers with high glass transition temperature increases slowly, and they can keep high breakdown strength at high temperatures.