Study on conduction current and space charge accumulation simultaneously in Ethylene Propylene Diene Monomer film

Abstract

This paper investigates the space charge distribution and external current performance of Ethylene Propylene Diene Monomer (EPDM) film simultaneously by an improved integrated PEA system. Through switching the space charge and current measurement circuits, the space charge and external current were detected alternately during the electric field of 60 kV/mm and 80 kV/mm. Small amounts of homocharges accumulated inside the sample. While, an obvious electron injection occurred from cathode (Al electrode), and they moved inside the sample. This leaded to an electric field distortion near the anode. However, hole injection seemed difficult to occur from anode (semiconducting layer). Based on the measured current density and the space charge distribution, we calculated the conduction current density distribution inside the sample. The results showed that a large conduction current occurred at the beginning of measurement, which is derived from the rapid electron injection and movement. Nevertheless, it decreased with the increase of time, indicating a uniform distribution of conduction current density (less than 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> A/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). In addition, the dissipation energy density caused by space charge and conduction current was also estimated during the field application. It indicated that a high power density appeared inside the sample at the beginning of measurement. However, it gradually decreased with the increase of time. This information reveals the energy loss dynamics caused by space charge during the electric stress, which is of great importance to evaluate the influential mechanisms of space charge on aging and insulation failure.