Experiment And Numerical Simulation Study On The Leakage And Diffusion Of SF₆ Heavy Gas

SF₆ is an inert gas with stable chemical properties and high electrical insulation strength,it is approximately 2.5 times the air insulation strength in a uniform electric field,its arc extinguishing capacity is approximately 100 times that of air,and it is widely used as an insulating materia in large-capacity transformers and high-voltage cables in power station.Under normal temperature and pressure,SF₆ is a high-density gas and its density is 5.1 times the air density,once the gas leakage and escape,will be deposition under the action of negative buoyancy,resulting in a significant increase in the concentration of harmful gases in the lower space?work area?of the workshop,and the long-term worker's health and the safe operation of equipment caused serious violations for years and months.However,there are many factors affecting the natural diffusion of the high density harmful gas such as SF₆,the mechanism is not clear,the concentration and distribution of pollutant in the work area are not be judged,therefore,the author has carried out the following research work:1.The concentration field of SF₆ in the restricted space with different leakage amount,different leakage position and different leakage angle was analyzed in a test bench model,and the experimental results show the variation of its concentration over time can be divided into two processes:rapid rise stage and slow rise stage,and the larger the leakage,the longer it takes to reach the slowly rising stage,and the greater the leakage,the thicker the high concentration area near the ground and the more obvious the concentration stratification.When the leakage point is located on the side of the body source,the concentration distribution is characterized by high concentration at the bottom,low diffusion height,a large amount of SF₆ will accumulate at the bottom of the model and move rapidly to other areas to form a large area of high concentration,and with the decrease of leakage height,the bottom concentration will increase correspondingly.When different angle leakage occurs in the test model,it is found that any leakage deviation from the outward normal the center point of the upper surface of the body source will cause the concentration of SF₆ in the model to be unevenly distributed,in which the deviation angle of 45 degrees will cause the maximum concentration of the bottom layer near the leakage port and become the most dangerous area in the model.However,When the leak angle is different,the most affected is the concentration of the lowest layer in the test model,at the higher position,the affected by the leakage angle is small.2.The selection of CFD turbulence model has always been the focus in the field of heavy gas research,the choice of model is directly related to the accuracy of CFD prediction results,therefore,in this paper,based on the experimental data,the leakage diffusion of SF₆ in test bench model was been simulation.The results showed that k-?model has the best predict effect,and it can best predict the leakage of SF₆ in the main transformer room of Ludila Hydropower station.3.This article has carried on the preliminary analysis to the ventilation strategy when the accidental leakage of SF₆ in the main transformer roomof a Hydropower Station.The research results show that when SF₆ accidental leakage in the main transformer room,the layout of the air outlet and air supply in the same side discharge SF₆ is superior to the performance of different side arrangement;and exhaust vents are arranged on both sides of the main transformer room to discharge SF₆ effect is relatively good;when the ventilation volume is constant,the exhaust outlet is too large or too small,which can negatively affect the discharge of the SF₆ in the main transform room;in terms of ventilation rate,with the increase of ventilation rate,the exhaust speed of SF₆ in main transformer room will speed up,but when the ventilation rate increase to8 time per hour,continue to increase the ventilation rate will have little effect on the SF₆discharge speed in the main transformer room,from the point of this article research results,the ventilation rate should take 8 times per hour.