直流电压下SF6中环氧复合绝缘的表面电荷积聚与衰减特性

Accumulation and Decay Characteristics of Surface Charges on Epoxy Composite Insulationin SF6 Under DC Voltage

为了研究直流电压下聚合物绝缘材料表面电荷的积聚和衰减特性,选择环氧复合绝缘材料为实验试品,采用对称平面压接电极,施加不同幅值的直流电压,利用静电探头测量了大气压SF6气体中不同充电时间下绝缘材料的表面电位分布。实验结果表明:在直流电压作用下,环氧复合绝缘表面会发生同极性电荷积聚,电极中心线上表面电位呈钟形分布,表面电位的峰值和半峰值宽度随电压幅值增加不断增加。在相同幅值电压下,低幅值时(<10kV),正极性下表面电荷密度较负极性下高;高幅值时(>10kV),负极性下表面电荷密度较正极性下高。随充电时间增加,电极中心线表面电位仍然呈钟形分布,和外施电压同极性的表面电荷密度较高且分布较为集中。表面电位的衰减分为两个阶段,符合双指数函数规律,初期衰减快,后期衰减慢,正电荷衰减速度大于负电荷,电压幅值越高,起始电位衰减越快,衰减完全所需要的时间越长。结合实验结果,分析认为表面电荷主要通过表面电导衰减。

In order to study the accumulation and decay characteristics of surface charges on polymeric insulation materials under DC voltage, the epoxy composite insulating material was selected as the experimental samples with symmetric planar electrodes. After the samples being charged under different voltage amplitudes with different duration in SF6 of atmospheric pressure, the surface potential distribution was measured with a Kelvin electrostatic probe. The results reveal that charges of the same polarity as applied voltage accumulate on the insulation surface. The surface potential of the center of electrode presents a bell-shaped distribution. The peak and half peak width of surface potential increase with the applied voltage amplitudes. When the applied voltage is low(<10 kV), the density of positive surface charge is higher than that of negative one under the same voltage magnitude, which is opposite when the applied voltage is high. When charging duration increases, the surface potential of the center of electrode also presents a bell-shaped distribution. The density of surface charge of the same polarity as applied voltage is higher and distributed intensively. There are two stages of surface charge decay, which satisfies a double exponential model. The decay rate is fast at earlier stage and slow at later stage. The initial decay rate is faster when the voltage amplitude is higher, but it takes much longer time to decay completely. The experimental results reveal that the surface charge decays mainly because of the contribution of surface conduction.