Temperature and flaw size-dependent electrical breakdown strength of high-temperature polymer dielectric materials

Polymer dielectric materials with high electrical breakdown strength over a wide temperature range are critical for many high-temperature applications. The breakdown strength of materials is affected by the temperature and flaw size. At present, few theoretical models can describe the combined influence of temperature and flaw size on the high-temperature breakdown strength well. The challenge is how to reasonably account for the effect of temperature-dependent flaw size. To counter this deficiency in the available literature, this work focuses on developing the theory to analyze the breakdown strength of materials with respect to temperature and flaw size. Herein, a theory called the electric-heat equivalence energy density principle, which defines a temperature-independent critical energy storage of breakdown, is proposed. By using the electric energy including parameters of dielectric constant, flaw size, and the equivalent heat energy including parameters of melting point and specific heat capacity to characterize the limit energy, a breakdown strength model of polymers considering effect of temperature and flaw size is developed. Each parameter in the theoretical models is a basic material parameter with clear physical meaning. All the theoretical models do not contain any fitting parameters. Our theory and theoretical models are verified by the comparison with experimental measurements. The agreement rate reaches more than 90 %, and some even reaches 98.9 %. The results of comparison indicate the predictive power of our developed models and the reasonableness of the definition of flaw sizes of materials at different temperatures. Our developed model can be used to determine the flaw size and the corresponding main microstructure that controls strength of materials at different temperatures.