直流电晕充电下环氧树脂表面电位衰减特性的研究

Research on surface potential decay characteristics of epoxy resin charged by direct current corona

介质材料表面电荷的积累和衰减行为是制约众多高压直流电力设备研制的关键因素.薄片状介质试样的表面电荷密度与表面电位近似呈线性关系,因此常通过表面电位衰减行为研究表面电荷的衰减特性.基于电晕充电、表面电荷沉积和脱陷、介质体内单极性电荷输运等3个物理过程,建立表面电位动态响应的物理模型.通过计算环氧树脂的表面电位衰减行为,得到栅极电压、相对介电常数和体电导率等对其表面电位衰减特性的影响.栅极电压越高,表面电位的衰减速度越快;环氧树脂材料参数典型值(相对介电常数3.93,体电导率10^(-14)S·m^(-1))下,归一化表面电位的衰减速率随时间变化的曲线可拟合为分段幂函数,其中,分段幂函数的特征时间、指数系数与栅极电压分别呈幂函数和线性变化关系.相对介电常数越大,表面电位的衰减速度越慢;环氧树脂相对介电常数典型范围(3—4)内,表面电位衰减时间常数由1720 s增大到2540 s,两者呈线性关系.体电导率越大,表面电位的衰减速度越快;环氧树脂体电导率典型范围(10^(-15)—10^(-13)S·m^(-1))内,表面电位衰减时间常数由24760 s减小到260 s,两者呈幂函数变化关系.

Surface charge accumulation and decay behaviors of dielectric materials are the key factors restricting the devel- opment of high voltage direct current power equipment. For flat samples, the density of surface charges deposited by corona can be regarded as a linear change with the surface potential. For this reason, the behavior of surface charge decay can be directly related to that of surface potential. According to the corona charging process, the surface charge deposition and detrapping process, as well as the charge transport process in the bulk, we may establish a physical model of dynamic response to the surface potential. Influences of grid voltage, relative permittivity, and bulk conductivity on the surface potential decay process can be obtained through calculating the surface potential decay behaviors of epoxy resin. The higher the grid voltage, the faster the surface potential decays. At the typical parameter value of epoxy resin （relative permittivity 3.93, bulk conductivity 10-14 S.m-1）, the normalized decay rate can be fitted by two straight lines in a log-log plot; moreover, the calculated results show a linear variation of power factors with the grid voltage, while the power function shows a relationship between the characteristic time and the grid voltage. The bigger the relative permittivity, the slower the surface potential decays. In the typical parameter area of epoxy resin （relative permittivity 3-4）, the surface potential decay time constant increases from 1720 s to 2540 s, showing a linear variation. Also the bigger the bulk conductivity, the faster the surface potential decays. In the typical parameter area of epoxy resin （bulk conductivity 10-15-10-13 S·m-1）, the surface potential decay time constant decreases from 24760 s to 260 s, showing a power function relationship.