In this work,gas insulated transmission lines（GIL）has been investigated using2D coupled multiphysics finite element method（FEM）,gas insulated transmission lines represent a new technology for high power transmission.Comparing with the overhead lines and XLPE-insulated cables,the advantages of GIL are obvious.The power transmission capacity of GIL is comparable with overhead lines,while the transmission losses are much lower.Because of the gaseous insulation,GIL has the lower reactive power,higher arc withstand capabilities and smaller transmission corridor.Method used in this work involved the multiple species transport technique to deal with heat transfer problems in high voltage power apparatus.The finite element method is employed to investigate the coupled eddy current and steady state thermal field using the commercial software ANSYS FLUENT and ANSOFT MAXWELL.Unlike the traditional models the surrounding air is also included in the solution region of GIL to avoid the need of constant convective heat transfer coefficients,thus multiple species transport technique is employed to deal with the problem of two fluids in a single model.Trifluoroiodomethane（CF₃I）is considered as a promising refrigerant alternative having promising dielectric properties comparable to those of.A mixture CF₃I/CO₂ is used as a potential alternative to which is used as an insulating material for many years.In addition,temperature dependent electric and thermal properties of the material are considered.Knowledge of the temperature rise plays an important role in understanding the improvement of the design process and in condition monitoring to keep GIL temperature at safety levels.The main point of this paper is to provide a simple and fast means of calculating the temperature rise of GIL.The skin effect of eddy current induced in the enclosure is considered.Considering the high capital cost,there is a great interest in accurate and fast methods for predicting the thermal behavior of GIL.The electric and thermal characteristic is strongly dependent on temperature,thus the temperature rise prediction of GIL is a coupled magneto-thermal problem.First of all the temperature rise in the bus bar is due to the joules losses in the conductor and induces eddy current in the enclosure.The power losses in a bus bar configuration are solved by electromagnetic field analysis using MAXWELL,which can be used as heat input to the thermal analysis which is performed by FLUENT,in which there is no need of convective boundary condition.The proposed model is applied to the steady state thermal analysis of single phase bus bar.Results from the model are validated against finite element simulations,yielding a good match.Power losses and temperature calculation from FEM and analytical method show satisfactory results.The model has proven to be sufficiently accurate and efficient for practical implementation in a design and condition monitoring program.