Simultaneous measurements of space charge distribution and external circuit current up to electrical breakdown in LDPE film

A space charge distribution and an external circuit current were simultaneously measured up to electrical breakdown in a 100 μm thick low-density polyethylene (LDPE) film with a semi-conducting electrode under dc voltage by using pulse electro-acoustic (PEA) method. We estimated an electric field distribution and a conduction current from these experiments. An electric field distortion due to a positive charge accumulation was observed at room temperature near the breakdown field. At 60°C and 90°C, however, an electric field distortion due to negative charge was observed, but the electric field distortions were not so large even near the breakdown field. The estimated conduction current reached to about 10 mA/m² before the electrical breakdown in each measurements. The obtained results suggest that the LDPE film becomes quasiconductive for negative charge at the field near breakdown and that the electrical breakdown is affected by the conduction current rather than the maximum electric field within the sample in the LDPE film