Direct Correlation between Space Charge and Conduction Characteristics of Low-density Polyethylene at Various Temperature

Abstract

The space charge distribution and current in low-density polyethylene (LDPE) have been measured by employing the pulsed-electro-acoustic (PEA) method. The measurement has been performed simultaneously under the temperature of 20 to 70°C for electric fields up to 50 MV/m in order to clarify the direct correlation between dynamic and pre-formed space charges and the conduction characteristics of LDPE. It was found that the conduction at high electric fields should be explained by different conduction models as temperature varied. At higher temperatures than 55°C, the conduction could be explained by diffusion-limited electrode injection current, but at 20°C by a kind of space-charge-limited current (SCLC). The power-law index of 4 was in reasonable agreement with the diffusion-limited electrode injection current and was influenced by pre-formed space charge. In addition, the numerical calculation about the experimental current and space charge distribution has been performed in order to correlate them. It was found that the hopping conduction of injected carriers had a deep relation with the formation of homo-space charge and the change of cathode field due to dynamic space charge played an important role in determining the time characteristics of the experimental current at high electric fields.