基于等温表面电位衰减法的直流电缆用低密度聚乙烯和交联聚乙烯陷阱电荷分布特性

Characteristics of Trapped Charge Distribution in LDPE and XLPE Used in DC Cables Based on Isothermal Surface Potential Decay Method

空间电荷积聚是影响直流电缆安全运行的重要原因,定量表征直流电缆用聚乙烯材料内陷阱电荷的分布特性并分析其内部陷阱产生的根源,对抑制空间电荷积聚、加强直流电缆安全可靠运行具有重要意义。为此,采用直流电晕充电法对低密度聚乙烯(low-density polyethylene,LDPE)和交联聚乙烯(crosslinked polyethylene,XLPE)薄膜试样进行了充电,以模拟直流加压时电荷的注入过程。通过考虑材料内入陷电荷的出陷规律,建立了1个等温表面电位衰减(isothermal surface potential decay,ISPD)模型。通过分析LDPE和XLPE薄膜试样的ISPD数据,获得了其内部陷阱电荷的分布特性,并进一步分析了LDPE与XLPE形态学特性和添加剂对陷阱形成的影响。结果表明:LDPE和XLPE中分别存在2个陷阱中心,即浅陷阱中心和深陷阱中心;LDPE中与XLPE中空穴深陷阱电荷密度都高于空穴浅陷阱电荷,即2者空穴陷阱电荷主要以深陷阱为主;XLPE中空穴浅陷阱电荷与空穴深陷阱电荷之间的数量差距减少,XLPE中空穴浅陷阱高于LDPE中空穴浅陷阱。交联副产物对XLPE内部陷阱的形成产生重要影响,且添加剂形成的空穴类型陷阱的深度并不完全相同。

Space charge accumulation is one of the major factors threatening the safe operation of DC cables. Quantita- tively characterizing the trapped charge distribution and understanding the root causes of the traps within polyethylene materials used in DC cables are of great significance to suppress space charge accumulation and secure DC cable opera- tion. Therefore, we charged low-density polyethylene （LDPE） and crosslinked polyethylene （XLPE） films using the DC corona charging method to simulate the injection process of space charges. Taking the de-trapping process of trapped charges in polymeric materials into consideration,we proposed a model based on isothermal surface potential decay （ISPD）. The distribution of trapped charges was obtained by analyzing the ISPD data of the LDPE and XLPE films, and then the effects of morphological characteristics of LDPE and XLPE and the effects of additives on the formation of traps were analyzed. The results show that there are two trap centers, i.e. a shallow trap center and a deep trap center for each film. In the samples, the density of hole-type deep trapped charges is higher than that of shallow ones, i.e. the hole-type trapped charges are mainly deep traps for both LDPE and XLPE. The quantity difference between shallow and deep hole-type charges is smaller in XLPE and the density of shallow trapped hole-type charges in XLPE is higher than that in LDPE. The crosslinking byproducts have an important influence on the formation of internal traps in XLPE, and the depth of the traps formed by additives is not exactly the same.