Influence of trap depths on space charge formation and accumulation characteristics in low density polyethylene

In extra high voltage transmission systems, the accumulation of space charges in polymeric materials have an important influence on the aging and breakdown of power equipments. It has been reported that space charges are mainly determined by trap distribution. Therefore, it is important to understand the influence of trap depths on space charges accumulation in insulating material. In this paper, based on charge migration, trapping and detrapping processes, an unipolar charge transport model has been adopted. The influence of trap depths on space charge in low density polyethylene can be obtained through solving the charge continuity equation, Poisson equation and first order charge trapping/ detrapping dynamic equation. The calculation results show that the free electron density and trapped electron density decrease gradually with the increase of sample position. With the trap depth increases, the total number of trapped electrons also increases, but the total number of free electrons decreases gradually. When the trap depth is larger than 1.1 eV, the total number of space charges in material keeps an equilibrium value. This research provides a theoretical guidance for diagnosing aging degree of insulating equipments in the future.