直流电场下C_4F_7N/CO_2与SF_6/N_2混合气体中铝质球形自由微粒放电敏感度对比分析

Comparative Analysis of Discharge Sensitivity by the Free Spherical Aluminum Particle in C_4F_7N/CO_2 and SF_6/N_2 Gas Mixtures under DC Electric Field

直流气体绝缘金属封闭输电线路(GIL)充SF_6混合气体或SF_6替代气体时,其绝缘性能将受到自由金属微粒的影响。本文重点针对C_4F_7N/CO_2以及SF_6/N_2混合气体,开展绝缘强度的影响分析。选用的实验气体组份为:C_4F_7N/CO_2(4%/96%)、SF_6/N_2(其中SF_6比例分别为20%、30%、50%和70%)以及纯SF_6气体,在球-碗电极直流电场下,开展微粒影响下的气隙击穿实验。提出微粒放电敏感度(DSP)的概念及定义,用以评估不同组分气体绝缘强度对金属微粒导致的局部电场强度剧变的敏感程度。实验结果表明,在0.1~0.5MPa气压范围内,不存在微粒时,4%C_4F_7N/96%CO_2绝缘强度与30%SF_6/70%N2混合气体相当;存在微粒影响时,4%C_4F_7N/96%CO_2混合气体的DSP值低于30%SF_6/70%N2混合气体的,而高于20%SF_6/80%N2混合气体的,且放电电流呈现双峰值特征。C_4F_7N/CO_2混合气体具有绝缘强度高、对微粒放电敏感度低的特性,这与C_4F_7N具有强电负性和高吸附系数有关。本文还结合微粒运动触发放电的物理模型,阐明了气隙击穿电流出现双峰特征的原因。

The electrical performance of DC gas insulation transmission line(GIL)using SF6 gas mixture or alternative gas as insulation medium will be deteriorated by free metal particles.The analysis of the factor affecting the insulation strength of SF6/N2 and C4F7N/CO2 gas mixtures is mainly performed in this paper.The breakdown experiments with particle were conducted with the ball-bowl electrode under the DC electric field,which included different gas compositions such as C4F7N/CO2(4%/96%)gas mixture,SF6/N2(volume ratio of SF6 includes:20%,30%,50%,and 70%,respectively)gas mixtures and pure SF6 gas.The concept of Discharge Sensitivity by Particles(DSP)was proposed to evaluate the sensitivity of the insulation strength of different compositions gas to the electric field distortion caused by metal particles.The experiment results show that in the pressure range of 0.1 to 0.5MPa,the dielectric strength of 4%C4F7N/96%CO2 is equivalent to that of 30%SF6/70%N2 in the absence of particle,while due to the presence of particles,the DSP of 4%C4F7N/96%CO2 gas mixture is higher than that of 20%SF6/80%N2 gas mixture and lower than that of 30%SF6/70%N2 gas mixture,accompanied by the appearance of discharge current of double peak.The high dielectric strength and low sensitivity to particle discharge of C4F7N/CO2 gas mixture is closely related to the strong electronegativity and high attachment coefficient of C4F7N.Combined with the physical model of moving particle-triggered discharge,the emergence of the double peak characteristics of gap breakdown current is also elaborated in this paper.