Temperature- and thickness-dependent electrical breakdown modulated by a coupling model of charge transport and molecular chain dynamics

Molecular chains with chemical defects acting as deep traps can be orientated by an electric field after trapping charges. Electric field force acts for a long period on a 'charged' molecular chain with occupied deep traps because of the long residence time of trapped charges. Based on the bipolar charge transport model, and the fact of thermally-activated motion of molecular chains and expansion of free volume when above the glass transition temperature, numerical simulation of coupling charge transport and molecular chain dynamics for polymeric insulating material under electro-thermal stress was conducted. Simulation results confirmed that temperature effects could enhance charge injection and charge energy, strengthening impact ionization, while also extending molecular chain displacement and reducing molecular chain fracture strength at high temperatures, thus synergistically forming chain scission and thereby the conductive paths. Other than the single factor of the space charge effect, the extended molecular chain displacement with increased temperature and thickness should be responsible for temperature- and thickness-dependent breakdown phenomena.