电场不均匀度对C4F7N/CO2混合气体雷电冲击放电特性的影响

Influence of Electric Field Non-uniformity on Breakdown Characteristics in C4F7N/CO2 Gas Mixtures Under Lightning Impulse

不同电场分布下混合气体雷电冲击放电特性是气体绝缘金属封闭输电线路(GILs)的设计基础,文中分别研究了稍不均匀电场(电场不均匀度系数f=1.6)和极不均匀电场(f=5.3和f=10.3)下C4F7N/CO2混合气体雷电冲击放电特性的变化规律。结果表明:稍不均匀场中,C4F7N/CO2混合气体的放电电压在高气压下出现微弱的饱和趋势,当气压小于0.4MPa时,其相对于在0.4MPa下SF6的绝缘强度达到了最大值,即随气压的升高,混合气体的相对绝缘性能并无显著提升;随着电场不均匀度的增大,C4F7N/CO2混合气体放电电压显著下降,且正极性放电电压远低于负极性,表现出对电场不均匀的极高敏感性;由此定义了电场敏感系数S,以表征绝缘介质在存在电场集中时放电电压的下降程度,研究结果表明,雷电冲击下气体介质对电场不均匀度的敏感性表现为C4F7N/CO2(5%~20%)>SF6>CO2。

The lightning impulse breakdown characteristics in gas mixtures under different electric field distributions are the design basis of gas-insulated equipment. Consequently, we investigated the lightning impulse breakdown characteristics of C4F7N/CO2 gas mixtures under lightning impulse in a quasi-uniform electric field(the factor of inhomogeneous field f=1.6) and an extremely non-uniform electric field(the factor of inhomogeneous field f=5.3 and 10.3). The research indicates that the breakdown voltage of C4F7N/CO2 gas mixtures increases linearly with increase of gas pressure in quasi-uniform electric field, and the saturated trend of breakdown voltage effect appears at high pressure. Its insulation strength relative to SF6 reaches its maximum at 0.4 MPa, that is, with the increase of air pressure, the relative insulation performance of mixed gases does not improve significantly. With the increase of the electric field non-uniformity, the breakdown voltage decreases significantly. The positive breakdown voltage is much lower than the negative. The sensitivity coefficient S is defined to characterize the decrease of discharge voltage of insulating medium when electric field is concentrated. The comparative analysis shows that the sensitivity of impulse breakdown characteristics of gas to electric field non-uniformity is C4F7N/CO2(5~20%)>SF6>CO2.