Simulation Of Electric Field And Temperature Field Of 550kV SF₆/N₂ Mixed Gas Isolating Switch

Isolating switch has the advantages of small size,compact structure,high safety,easy maintenance,and long overhaul period.It is widely used in substations.The simple structure of the isolation switch is very important to control and protect the safety of transmission lines.However,due to a series of problems such as gas leakage,insulation failure and heat generation,the stable operation of the isolation switch is seriously affected,thereby affecting the safety of the GIS and the entire power grid,and even causing harm to the human body and the environment.With the steady increase of voltage levels,insulation problems and conductive loop overheating problems become more and more difficult,while traditional calculation methods and experimental methods can only estimate or measure the temperature rise value,and cannot clearly observe the specific temperature distribution details,which is difficult to meet the development needs.Therefore,the electromagnetic and temperature field simulation of the mixed gas isolating switch is of great significance to the development of the isolating switch.The two-dimensional and three-dimensional electric field simulation model of the 550kV SF₆/N₂ mixed gas isolating switch is established in this thesis,and the electric field distribution is analyzed and optimized through the finite element analysis method.The magnetic-thermal indirect coupled method is used to calculate the current density and loss of the conductive loop and shell under rated conditions,and then the temperature rise of the isolation switch is calculated.Finally,the separation variable method is used to analyze the influencing factors of temperature rise.The research results and methods can shorten the R&D cycle and save R&D costs,which provides technical support for the research of isolation switches.In order to know the insulation performance and temperature rise of the isolating switch,According to the simulation results of electric field,the distribution of electric field intensity in the gas chamber is analyzed in this thesis,and the calculation proves that the model satisfies the insulation requirements.Secondly,the influence of positive and negative voltages and different distances on the field strength distribution is researched,the relative position of the dynamic and static arc contacts are calculated,and the dynamic and static arc contacts are optimized.Finally the grid evaluation standard is proposed,the temperature field distribution of the conductive circuit and the shell of the isolating switch are analyzed,and the factors affecting the loss of the shell have been studied preliminarily,then the effects of changes in arc contact material,power frequency,ambient temperature and load current on temperature rise are discussed.According to the above research results,it can be concluded that:the electric field distribution in the gas chamber is uniform,only around the rounded corners of dynamic and static arc contacts the electric field intensity is larger.Through optimized design,the most suitable corner radius of the dynamic and static arc contacts are 2mm and 14mm.Compared with before optimization,the maximum field strength value is reduced by 16.98%,and the electric field strength distribution is more uniform,which provide a reference for the design of the isolating switch.Loading the positive and negative voltages has no significant effect on the potential distribution and electric field distribution.However with the increases of distances,the maximum value of electric field intensity changes in a power function（power is less than0）,the movement of the dynamic arc contact causes the relative action point of the dynamic and static contacts to change.When the distance is greater than 40%,the change tends to be stable.When the aluminum shell is used on isolation switch the and the arc contact material is copper-tungsten alloy,the temperature rise of the isolation switch is lower,which accord with the national standard.Small changes in frequency have no major impact on temperature rise,the change in ambient temperature only causes the corresponding amplitude change of the temperature in conductive loop,and the load current has a non-linear positive correlation with the temperature of the conductive loop.