低密度聚乙烯空间电荷与电导电流的联合测量

Combined Measurement of Space Charge and Conduction Current in Low Density Polyethylene

聚乙烯非常容易积累空间电荷,造成聚乙烯绝缘电缆用于高压直流输电时容易出现绝缘劣化和使用寿命减少的问题。为了研究绝缘材料在直流电场下的空间电荷特性与电导特性,考虑到由于外电流存在位移电流分量,对于同一块试样分别测量得到的结果并不能进行严格的联合分析,基于脉冲电声法(pulse electro acoustic,PEA)原理设计了一套能够对平板试样进行"同区分时"测量空间电荷和外电流的实验装置,联合测量了低密度聚乙烯(low density polyethylene,LDPE)在室温下的空间电荷和高场电导。实验结果表明:随着施加场强的升高,阳极异极性空间电荷逐渐增加,阴极由同极性注入转变为异极性空间电荷积累,这与材料内部的杂质解离以及不同电极材料的选取有关。低电场条件下位移电流在外电流中所占的比例大于电导电流,传导电流密度与电场强度的关系也符合空间电荷限制电流(space-charge-limited current)理论。

It is so easy for polyethylene to accumulate space charge that there is a problem of insulation deterioration and service life reduction for polyethylene insulated HVDC cable. In order to research the properties of space charge and conduction current of insulation materials under DC electric field,and taking the fact into account that for the same piece of samples,separate measurement results cannot be used for combined analysis strictly because of the displacement current component in external current,a newtype of equipment based on pulse electro acoustic method（ PEA） and the＂same region time division＂technique is designed to perform simultaneous measurement on plate specimen. The measurement results of space charge distribution and high electric field conduction in lowdensity polyethylene（ LDPE） plate sample are presented in this paper. The experimental results showthat with the increase of electric field,increasing heterocharges around anode is accumulated,and the transition from heterocharges to homocharges around cathode can be observed. The phenomenon has relationship with impurity dissociation and different electrode materials. Displacement current density at room temperature under the condition of lowelectric field among the external current ratio is greater than that of the conduction current. The relationship between conduction current density and the electric field intensity also conforms to the Space Charge Limited Current theory.