Quantum Chemical Calculation Studies on Electrical Conductivity Increasing in DC Thermal Pre-Breakdown Process for Low Density Polyethylene

Abstract

The LDPE impregnated with acetophenone (AP), one of cross linking byproducts, under a high electrical stress of E=150kV/mm caused a breakdown by the consumption electric power density of κE²=2.5W/cm², which was measured by using the advanced technique combined with the space charge measurement (PEA system) and the terminal current measurement. The consumption electric power (κE²) leads to a thermal breakdown of LDPE specimen, where κ is an electric conductivity. The conductivity of LDPE with AP is much increased because the injection barrier of electron carrier from cathode decrease 4.25eV to 2.60eV and the injection barrier of hole carrier from anode also decrease 3.37eV to 2.54eV. These injection barrier height were calculated by Gaussian 09 software of Quantum Chemical Calculation. It is proposed the thermal breakdown mechanism that the conductivity (κ) of LDPE with AP increases, the consumption electric power (κE²) also increases, the temperature of filamentary conductivity path increases to a melting temperature, and then the breakdown is occurred.