DIRECT CORRELATION BETWEEN SPACE-CHARGE AND CONDUCTION CHARACTERISTICS OF LOW-DENSITY POLYETHYLENE AT VARIOUS TEMPERATURE

The space charge distribution and current in low-density polyethylene (LDPE) have been measured by employing the pulsed-electro-acoustic (PE A) method. The measurement has been performed simultaneously under the temperature of 20 to 70 degrees C for electric fields up to 50 MV/m i n order to clarify the direct correlation between dynamic and pre-form ed space charges and the conduction characteristics of LDPE. It was fo und that the conduction at high electric fields should be explained by different conduction models as temperature varied. At higher temperat ures than 55 degrees C, the conduction could be explained by diffusion -limited electrode injection current, but at 20 degrees 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 cu rrent 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 fou nd that the hopping conduction of injected carriers had a deep relatio n with the formation of home-space charge and the change of cathode fi eld due to dynamic space charge played an important role in determinin g the time characteristics of the experimental current at high electri c fields.