Studies of the Effect of Temperature on the Charge Trapping and De-trapping Processes of Polymeric Insulators through Depolarization Current Measurements

Formation of space charge in polymeric insulation is a critical issue in the design of high voltage electric systems. Accumulation of space charge accelerates the material aging and may lead to premature breakdown of the insulation. Therefore, it becomes increasingly important to understand the charge injection, trapping and de-trapping processes in dielectric under application of high voltage. However analysis of charge trapping and de-trapping is very difficult due to material properties and also the fact that the measurement of space charge itself is a very complicated issue. Most of the trapping and de-trapping investigation in literature has been performed through indirect means, by measuring the space charge distribution in a dielectric specimen under charging and discharging conditions. The effect of temperature on the trapping and de-trapping properties of polymeric insulating materials has also received limited attention. In this paper, the charge trapping and de-trapping behavior of low density polyethylene (LDPE), a widely used polymeric material for electrical insulation purpose, have been investigated using a direct method based on the depolarization characteristics of a stressed sample. A model has been developed to obtain the trapped charge distribution according to their energy level in the sample directly from the depolarization current. The measurements were performed at different temperature to study the effect of temperature. It was observed that temperature plays a critical role in charge injection, trap formation, trapping and de-trapping.