Space Charge Modelling in Solid Dielectrics under High Electric Field Based on Double Charge Injection Model
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Space Charge Modelling in Solid Dielectrics under High Electric Field Based on Double Charge Injection Model G Chen and Su Han Loi School of Electronics and Computer Science University of Southampton, United Kingdom ABSTRACT Present study aims to develop a clear insight on factors that influence space charge dynamics in solid dielectrics through a numerical simulation. The model used for the simulation is proposed by Alison and Hill [1] which describes charge dynamics as a result of bipolar transport with single level trapping. In this model, a constant mobility and no detrapping have been assumed. The simulation results show that carrier mobility, trapping coefficient and Schottky barrier have a significant effect on the space charge dynamics. Many features of space charge profiles observed by experiments have been revealed in despite of over simplistic model. More importantly, the simulation allows us to study the role of each individual parameter in the formation of space charge in solid dielectrics, so that the experimental results can be better understood. INTRODUCTION One of the major issues in the electricity generation and supply industries is the catastrophic failure of high voltage insulation in power equipment. The problem has received much interest over the last decade as the reliability of power systems has attracted attention of the public. Polymeric materials have been replacing traditional insulating materials due to their excellent mechanical, chemical and electrical properties. However, like any other materials, they are prone to develop an inevitable effect of electrical and chemical degradation after some long-standing operation. It is generally believed that the occurrence of space charge within polymeric materials would introduce an early ageing effect in which the life expectancy of the insulation is greatly affected. Consequently, space charge measurements in polymeric materials have been extensively explored in last two decades. Various mechanisms have been proposed in the process of pursuing understanding observed phenomena. However, majority of the published work concentrates on experimental results and their explanation. Due to the physical and engineering significance of space charge phenomenon, the research on this topic has gradually extended to the numerical-computational technique of analyzing the space charge dynamics via simulation. Various space charge models have been proposed over the years. Earlier models were been extensively reviewed by Lampert and Mark [2] and Mott and Davis [3]. Recently, there have been new developments in charge transportation models following the emerge of new experimental evidences [1, 4-5]. Each model has its own merits and drawbacks. Model proposed by Kaneko et al [5] is mainly used to describe the phenomena observed at fields exceeding 100 kV/mm where so called packet charge is observed. On the other hand, the model proposed by Fukuma et al [4] was based on hopping transport mechanism and its applicability to real system has been hampe
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