直流电压下SF6气体中电极覆膜后金属微粒启举场强的计算分析

Calculation and Analysis of Lifting Field of Metallic Particle on Dielectric Coated Electrode in SF6 Under DC Voltage

电极覆膜是直流GIL中提高金属微粒启举场强的一种重要措施,研究覆膜后启举场强的计算能够为实际GIL覆膜选择提供理论支撑。Parekh启举场强计算模型未考虑薄膜相对介电常数、微粒与薄膜间发生局部放电时电子崩头部空间电荷的影响,且微粒受到的电场力计算公式与实际不符,对此进行了改进。基于改进模型获得了不同SF6气体压力、薄膜材质及厚度组合下的计算结果,并开展实验验证了改进模型的准确性。考虑薄膜相对介电常数后微粒与薄膜间发生局部放电的场强降低,考虑空间电荷后微粒带电量会明显增加,从而提高了启举场强计算的精确度;此外,新的电场力计算公式更能揭示覆膜影响微粒受力的物理本质。分析表明：微粒带电量减少和受到向下的电场力是电极覆膜提高启举场强的两个原因。

Dielectrically coated electrode is an important way to improve lifting field of metal particles in DC GIL,and study on the lifting field calculation with dielectric coated electrodes can provide a theoretical support for the selection of coating in practical GIL.The effect of coating dielectric constant and the space charge in the electron avalanche head when the partial discharge occurs between particles and dielectric coated electrodes have not been considered in the Parekh calculation model about lifting field,and the calculation formula of electrostatic force is contrary to what it actually is,thus we improved the model.Results under different groups of SF6 gas pressure,coating material and thickness were gained based on the optimization model to verify the accuracy of optimization model.The electric field of partial discharge between particles and dielectric coated electrodes is decreased with considering the effect of coating dielectric constant,particle charge increases obviously when space charge is taken into account,improving the computing accuracy of lifting field;moreover,the new electric field force calculation formula can better explain the physical properties of coating＇s effect on electric field force.It is concluded that the decreasing of particle charge and downward electric field force are causes for enhancement of lifting field.