Electrode influence on DC conductivity measurements of low density poly ethylene

In high voltage DC applications one of the most critical parameters of insulation materials is the conductivity. It is however challenging to measure conductivity accurately, since it is influenced by composition, morphology, sample thickness, temperature, electric field strength and electrode material. There is no standard electrode material used for electrical characterization of insulation in research. It is known that different electrode materials give rise to different conduction currents and different space charge inside a polymer sample. It is also believed that oxide layers on metal electrodes influence the activation energy of the interface between the polymer sample and the metal electrode. In the present work, a pure non-stabilized LDPE was used to investigate different electrode materials. The following materials were investigated: brass, copper, aluminum, gold, silver and semi conductive polymer. The method of application of the electrodes onto the polymer samples was also varied. The results indicate that the contact material and the method how to connect the material to the polymer sample had an influence on the time behavior of the DC conductivity during 24h of polarization. It could be shown that the applied electrical field influenced the crystal structure of the sample.