Research And Test Of CF₄/CO₂ Lightning Impulse Breakdown Characteristics And Temperature Rise Characteristics

With the rapid development of our country’s economy,the demand of electricity is increasing,and the development of power system is increasingly moving towards large units,large capacity,ultra-high voltage and long-distance.The increase in the voltage level of power transmission grids puts forward higher requirements for the insulation of power equipment.However,due to the high Global Warming Potential（GWP）and high liquefaction temperature of SF₆,SF₆ was listed as one of the six restricted gases in the 1997 Kyoto Protocol.Therefore,it is great significance to find a new type of environmentally friendly gas that can replace SF₆.CF₄ has good insulation properties and a low greenhouse effect index,and is low in cost and high in liquefaction temperature.It is a new type of environmentally friendly gas that has the potential to replace SF₆.The new type of gas formed by mixing CF₄ and CO₂ can not only reduce the greenhouse effect index but also further reduce the cost,and has certain engineering use value.In this article,the lightning impact test Test temperature and the nature of CF₄/CO₂ mixed gas was studied,specifically as follows:First,Research the thermodynamic parameters of CF₄/CO₂ mixed gas.The Chung method is used to calculate the specific heat capacity,viscosity and thermal conductivity of the CF₄/CO₂ mixed gas under different mixing ratios at different pressures and temperatures.The heat dissipation form and heat loss of GIS metal enclosed busbar are analyzed and calculated.Second,by designing three pole plates with different electric field unevenness coefficients:cylinder-cylinder,plate-plate,and ball-ball,a lightning impact test platform was established,and a gas test plan and operation process were formulated.The electrostatic field simulation analysis is carried out on the three different electric field non-uniform coefficients,and the electric field non-uniform coefficient is calculated,and the appropriate distance between the electrodes is selected for the lightning impact test.Then,the mixed gas CF₄/CO₂ and pure SF₆ at different mixing ratios were subjected to positive and negative lightning impact tests at 0.3 MPa to 0.6MPa.The results show that the insulation characteristics of the CF₄/CO₂ mixed gas of0.5MPa～0.6MPa and the pure SF₆ of 0.3MPa are roughly equivalent under a uniform electric field.Under the uneven electric field,only 0.6MPa CF₄/CO₂ mixed gas and0.3MPa pure SF₆ insulation characteristics are equivalent.Third,using the previously calculated CF₄/CO₂ mixed gas is substituted into the finite element simulation software.Then,the mixed gas CF₄/CO₂ and pure SF₆ at different mixing ratios were subjected to a temperature rise test of 3150A at 0.3MPa to0.6MPa.The result shows that the temperature rise characteristics of CF₄/CO₂（4:6）at0.6MPa and pure SF₆ at 0.3MPa are roughly the same,while the temperature rise characteristics of CF₄/CO₂（5:5）under 0.5MPa～0.6MPa are approximately the same as that of pure SF₆ of 0.3MPa.Finally,combining the results of the lightning impact test and the temperature rise test,it can be concluded that the mixed gas CF₄/CO₂（5:5）under 0.6MPa can replace the pure SF₆ of 0.3MPa.Preliminary verification of the engineering use value of mixed gas CF₄/CO₂.