Study On Insulation And Arc Extinguishing Performance Of 252kV SF₆/CF₄ Gas Mixture Circuit Breaker In Cold Area

The temperature reaches to-40℃,some areas reach-50℃in the north cold area of China.The SF₆ gas in the circuit breaker liquid under the condition of low temperature,gas pressure and density,and the strength of the insulation and interrupting capability of circuit breaker are reduced,affect the normal operation of the circuit breaker.CF₄ gas with low liquefaction temperature,high insulation strength and strong arc extinguishing ability in SF₆ gas can effectively solve the problem of low-temperature liquefaction of SF₆ circuit breaker.This thesis investigates the insulation and arc extinguishing performance of 252kV SF₆/CF₄ gas mixture circuit breaker,research achievements applied directly used in design research and development of 252kV SF₆/CF₄ gas mixture circuit breaker with self intellectual property rights in China.The study is shown as follows:（1）The mathematical model of SF₆/CF₄ gas mixture was established,numerical calculation of saturated vapor pressure and density of gas mixture was carried out,maximum charging pressure and content of gas mixture at different working temperatures were determined.low temperature pressure characteristic measuring device of SF₆/CF₄ was set up,accuracy of the theoretical calculation of saturated vapor pressure of gas mixture is verified,and the thermal properties of gas mixture under different temperatures,pressures and mixing ratios were obtained.（2）The influence of mixing ratio,synergistic effect on SF₆/CF₄ gas mixture breakdown voltage was studied and breakdown criterion of mixed gas insulation is presented.The selection method of gas pressure and proportion of gas mixture circuit breaker is proposed and the optimum mixing ratio of the gas in the gas mixture circuit breaker is obtained.The key components such as the contact and shield of the arc chamber are optimized and the insulation structure of arc extinguishing chamber was determined.（3）The mathematical model is established to calculate the flow field of SF₆/CF₄ gas mixture circuit breaker,The gas flow field of 252kV SF₆/CF₄ gas mixture circuit breaker was studied by using the calculation results of the thermal property parameters of the mixture,the influence of mixture pressure and mixture ratio on pressure characteristics and gas density was obtained.The gas density of the weakest position of the gas mixture circuit breaker is given by analyzing the change of gas pressure,temperature and density,the dielectric recovery characteristics of circuit breaker is obtained according to the breakdown criterion.The dynamic breakdown voltage measurement circuit of the gas mixture circuit breaker is built,and the dynamic insulation characteristics of the gas mixture circuit breaker are obtained.The circuit breaker proportions of mixed gas used in-40℃and-50℃low temperature condition were proposed.（4）252kV SF₆/CF₄ gas mixture circuit breaker which can be used in the cold region was developed based on the theoretical and experimental results of SF₆/CF₄ gas mixture physical property parameter,insulation and arc extinguish performance.The power frequency,lightning impulse,50kA short-circuit breaking and current temperature rise test of 4400A are carried out,All the experiments were carried out successfully,and the rationality of SF₆/CF₄ mixture ratio scheme and the structure design of the arc extinguishing chamber was verified.The research achievement of SF₆/CF₄ gas mixture circuit breaker insulation and arc characteristics not only can be used in the gas mixture circuit breaker in product development design,and can be applied in the development of new alternative gas circuit breaker.