Charge Traps Depended Space Charge Dynamics and Electrical Breakdown Characteristics of Polymer Insulating Materials

Abstract

Electrical breakdown of insulating materials unavoidably occurs in power equipment, which endangers the safe operation of power systems. Recent investigations suggest both shallow and deep traps contribute to improved breakdown performance of insulating materials. This contradiction implies that no uniform conclusion is formed at present stage, and thus suggesting the influence of charge trap on electrical breakdown and its related space charge dynamics are still to be further investigated. Here in this paper, electrical breakdown experiments were firstly conducted on three typical polymer insulating materials (low density polyethylene, polypropylene and polyimide). Then, charge trap depth and trap density of the three polymers were characterized by isothermal surface potential decay experiments, and the obtained information of charge traps were linked to breakdown results. After that, space charge dynamics in electrical breakdown processes of low density polyethylene with variations of charge trap depth were systemically simulated based on an improved bipolar charge transport model. It is found that the electrical breakdown strength of insulating materials are strongly related to trap depth of space charges, as deep charge traps corresponds to enhanced electrical breakdown strengths. The profile of homo space charges under DC stress is controlled by charge trap depth, and space charge induced electric field distortion dominates the DC breakdown performance of insulating materials. A turning point of DC breakdown strength is found around 0.58 eV of trap depth, as both shallower traps and deeper traps lead to increased electrical breakdown strengths.