直流电压作用下极不均匀电场中SF_6/N_2混合气体局部放电起始特性研究

Partial Discharge Initial Characteristics of SF_6/N_2 Mixture in Extremely Inhomogeneous Electric Field under DC High Voltage

为了解决直流气体绝缘输电线路(GIL)中绝缘气体SF_6高温室效应、价格昂贵等问题,采用SF_6与N_2混合绝缘的解决方案。针对直流GIL中极不均匀电场的情形,搭建直流高压试验平台,研究了SF_6/N_2混合气体在不同SF_6体积分数、不同电压极性和不同气压条件下的局部放电起始特性。结果表明:气压为0.3 MPa电场畸变特别严重时,SF_6/N_2混合气体的起始放电电压(U_0)会高于纯SF_6气体的起始放电电压,且电场畸变越严重,混合气体U_0高于纯SF_6气体所需的SF_6含量越低;曲率半径(r)为20、50μm的尖端气体相对绝缘强度(k)随SF_6含量变化的趋势一致,呈现双峰形状,r为100、120和160μm的尖端k随SF_6变化呈现单峰形状,且负极性电压下的k高于正极性电压下的k;r为20μm的尖端在SF_6浓度为20%时,0.1～0.3 MPa气压范围内混合气体U_0高于纯SF_6气体,气压为0.4 MPa时,混合气体U_0为纯SF_6气体的95%,已基本达到纯SF_6气体的绝缘强度。

To solve the problems of high greenhouse effect and high price of SF6 in DC gas insulated line(GIL), a solution scheme of mixing SF6 and N2 is proposed. Aiming at the extremely inhomogeneous electric field, a DC high voltage test platform is constructed to analyze the initial discharge characteristics of different SF6/N2 ratios under different voltage polarities and gas pressures. The results show that in the case of 0.3 MPa, the partial discharge initial voltage(U0) of SF6/N2 mixture is higher than that of SF6 when electric distortion is really serious, and the more serious the electric field distortion is, the less the SF6 is needed. For 20 μm and 50 μm electrode tip, the gas relative dielectric strength k trends towards φ(SF6), and its curve shape is doublet;for 100 μm, 120 μm and 160 μm tip, the shape is singlet, and k value under negative voltage is larger than that under positive voltage. For 20 μm tip in 20% SF6, when pressure is between 0.1 MPa and 0.3 MPa, the U0 of SF6/N2 is larger than that of SF6, and when pressure is 0.4 MPa, the U0 of SF6/N2 is 95% of that of SF6.