空间电荷对低密度聚乙烯电气击穿特性的影响

为解决聚乙烯用作电线电缆绝缘材料时所受空间电荷问题的困扰,采用在低密度聚乙烯(low density po-lyethylene,LDPE)试品上施加直流预电压使其中积聚一定量的空间电荷,然后测量试品击穿强度的方法,研究了空间电荷对LDPE击穿特性的影响。结果表明,与未经过预电压处理的LDPE的击穿强度相比,在经过较低场强(50 kV/mm)预电压处理后,预电压与击穿电压极性相同时击穿强度提高了约9%,极性相异时击穿强度降低约14%;而经过较高场强(150 kV/mm)预电压处理后,预电压时LDPE中出现空间电荷包现象,预电压后同极性击穿强度提高约19%,而异极性击穿强度反而上升约16%。分析认为空间电荷包在LDPE中的运动导致了部分空间电荷的中和,使得空间电荷积聚量减少,同时LDPE中可能的缺陷得到了一定程度的老炼而使介质得到了均匀化,从而使LDPE的击穿强度得到了提高。

Effects of Space Charges on DC Breakdown in Low Density Polyethylene

Polyethylene is widely used in electrical wires and power cables as a polymeric insulating material.To deal with the prestressing effect in polyethylene,effects of space charges on breakdown is studied.By applying a DC electrical field on low-density polyethylene(LDPE) specimens,space charges began to accumulate within the LDPE specimens.Then the DC breakdown strength of the specimens was measured within a short period of time after the electrical field was removed and the effects of space charges on DC breakdown in LDPE were analyzed.The experimental results showed that,compared with the DC breakdown strength of LDPE specimens without pre-stressing,the DC breakdown strength of LDPE specimens pre-stressed by a low field of 50 kV/mm,increased by 9% when the polarity of breakdown field was the same as that of the pre-stressing field,and decreased by 14% when the polarity was opposite to that of the pre-stressing field.Furthermore,when LDPE specimens were pre-stressed by a high field of 150 kV/mm,space charge packets came into being and traveled through the specimens,and after the electrical field was removed,the breakdown strength of homo polarity increased by 19%.However,the breakdown strength of hetero polarity did not decrease.Instead,it increased by 16% compared with that of LDPE specimens without pre-stressing.The results indicate that the movement of space charge packets in LDPE specimens bring the neutralization of part of the space charges and therefore decrease the accumulation of space charges in LDPE specimens.Meanwhile,the movement of space charge packets may contribute to the uniformity of the traps in LDPE,which is helpful to the increase of the breakdown strength.