Power Frequency Breakdown Characteristics of SF6/CO2/N2 and CF3I/NO2/N2 at Different Mixing Ratios

Abstract

Although SF6 gas has good insulation performance, due to its intense greenhouse effect, the search for alternative gases of SF6 has become a research hotspot of scholars at home and abroad in recent years. In this paper, the discharge parameters of SF6/CO2/N2 and CF3I/CO2/N2 gas mixtures with different ratios are calculated by Boltzmann equation analysis method. Preliminary prediction of insulation strength of mixed gases at different mixing ratios is carried out so as to select the mixed gases with better insulation performance and larger substitutability for in-depth research. Introduction Because of its good insulation and arc extinguishing performance, electronegative SF6 gas insulating medium has been widely used in power equipment, and its usage has increased year by year [1-3]. However, the potential global warming potential (GWP) of SF6 is 23,900 times that of CO2, and the lifetime of SF6 in the atmosphere is 3,200 years [4-7], which has a cumulative effect on global warming [8]. Therefore, the 1997 Kyoto Protocol designated SF6 as a restricted high temperature room effect gas. By 2020, the use of SF6 needs to be gradually reduced. In view of the increasingly more severe global warming, it is urgent to find new gases with insulation performance equal to or better than SF6 and lower greenhouse effect index to replace SF6. CF3I and its mixtures are widely concerned in the field of electrical equipment as a potential substitute for SF6 due to their high insulation performance and small GWP[10]. With the purpose to facilitate the optimal design of mixed gases, it is a hotspot to calculate the insulation performance of SF6 at various mixing ratios by theoretical analysis before an experiment. At present, the research object of SF6 substitute gas at home and abroad mainly concentrates on binary mixture gas, and there is little research on the insulation performance of ternary mixed gas by experiment and simulation. Therefore, the critical breakdown field strength of SF6/CO2/N2 and CF3I/CO2/N2 ternary mixtures with different ratios is simulated by Boltzmann equation analysis method. The influential laws of CO2/N2 mixing ratio (20%-80%) on the power frequency breakdown characteristics of CF3I and SF6 mixtures under uniform electric field and 0.1 MPa pressure is researched. The results of this paper can provide a reference for the research of SF6 alternative gases. Calculation Method of Critical Breakdown Field Intensity In this paper, Boltzmann equation analysis method is used to calculate the critical breakdown field intensity of mixed gases. The calculation principle of this method is as follows: Under uniform electric field, the distribution function of electrons in six-dimensional phase space satisfies the Boltzmann equation: \uf05b \uf05d V f e v f E f C f t m \uf0b6 \uf02b \uf0d7\uf0d1 \uf02d \uf0d7 \uf0d7 \uf0d1 \uf03d \uf0b6 (1) Where, v is the electron velocity, e is the electron charge, m is the electron mass, E is the electric field intensity, V \uf0d1 is the operator of the velocity gradient, and C is the change rate caused