State Awareness And Fault Location Of Mixed Gas-insulated Transmission Lines Based On Thermal Characteristics

As an effective means for large-scale long-distance transmission,Gas-insulated transmission lines（GIL）are receiving more and more attention.These lines have the advantages of high voltage level,large transmission capacity,low loss,and no significant safety accidents,they also have higher reliability during the operation.With the increase of voltage levels and load requirements,the reliable operation of GIL has received widespread attention.Based on this,the thesis proposes a multi-physics coupling model to study the thermal characteristics of GIL.The characteristics of SF₆/N₂ gas mixtures is researched through the model.Meanwhile,the state awareness and fault location are studied.In the end,the requirements of reliable and safety operation are realized.Considering that SF₆ is a potent greenhouse gas,the hazard of SF₆ to the environment can reach 23500 times that of CO₂,and SF₆/N₂ gas mixtures can greatly reduce the consumption of SF₆.Therefore,SF₆/N₂ gas mixtures are preferred to serve as the insulating gas for its environmental friendliness and good insulation.Since heat transfer analysis is very useful for ascertaining the appropriate temperature rise range,which can ensure the safe operation and extension of remaining useful life of GIL,it is essential to study the thermal properties of SF₆/N₂ gas mixtures.Nevertheless,very few studies investigate on the temperature field of SF₆/N₂ gas mixtures under ideal conditions.To reflect the heat transfer characteristics accurately,in this thesis,by using the finite-element method and multi-physics coupling,the heat transfer properties in the GIL is analyzed by using a three-dimensional axisymmetric GIL model.By varying the SF₆/N₂ mixing ratio and observing the corresponding heat transfer characteristics,the mapping between SF₆/N₂ mixing ratio and the temperature rise is obtained by using the model.Furthermore,the mappings are studied under different gas pressures,line currents and ambient temperatures,which correspond to different real-life operating conditions.Furthermore,the effectiveness of the model is verified through experiments,the proposed strategies can effectively give guidance of choosing proper SF₆/N₂ mixing ratio for desired temperature rise,and thus having great values of practical applications.SuTong GIL is a critical connection for the UHV AC loop network in East China,so its state awareness and fault location are extremely important for the operation and maintenance.Based on the temperature rise effect of the GIL,this thesis defines the ratio of heat-temperature and the change rate of the ratio of heat temperature as the characteristic parameters.Furthermore,a gas chamber edge computing system is designed.First,the temperature data of the gas chamber are collected through the sensor in real-time.The characteristic parameters are calculated at the edge nodes.Based on the boundary equations,the state is divided into the normal,the critical alert and the abnormal state.The characteristic of the gas chamber is stored in the cloud server.Moreover,the fault section location can be achieved by studying the correlation of the temperature transition characteristics of the gas chamber in the whole line.Then the three-dimensional finite element model is established through COMSOL.The current change is used as the simulation situation,the trend and value range of the characteristic parameters in different states are obtained.The results show that the method proposed in this thesis can awareness the situation of the gas chamber in the whole GIL line accurately and quickly.It can also realize the fault section location.The reliability of the system is verified through the experiment.Finally,in practice,through the real-time calculation of the characteristic parameters at the edge nodes,the GIL state awareness and fault location can be realized in the cloud server.The thesis contains 43 figures,13 tables and 92 references.