Research On The Coupling Of Thermal Field And Flow Field In The Locomotive Traction Transformer

The running state of locomotive traction transformer is directly related to smooth operation of electric locomotive,and the temperature in the working process not only affects the insulation performance of transformer,but also reduces the service life of transformer.As one kind of oil-immersed transformers,the loss induced by the magnetic field of locomotive traction transformer distribute in the core,oil tank and other magnetic materials and the ohmic loss in the windings are the internal heat sources of transformer.The flow of transformer oil flow forces the internal temperature rise to distribute uniformly.By carrying out the combination simulation between oil flow velocity and temperature distribution effectively in the transformer design stage,the risk of insulation failure caused by local over-heating of traction transformer can be reduced.Therefore,this thesis took a JQFP type and 25 kV locomotive traction transformer as the research object,and established the three-dimensional magnetic field,three-dimensional temperature field and flow field simulation model of the transformer based on the reasonable simplification and assumption of the model.The simulation calculation and analysis in the three-dimensional main magnetic field,magnetic leakage field,temperature field and flow field were carried out.The main research contents are as follows:Firstly,the physical model and mathematical model of multi-physical field among the coupling of magnetic,flow and heat field in the traction transformer were built up.In the simulation calculation,the electromagnetic field was solved by finite element method,the flow field coupled directly with temperature field was solved by finite volume method,and the magnetic field and heat-flow field were coupled indirectly.The magnetic characteristics and loss characteristics of silicon steel sheet in the transformer core and solid steel in the oil tank were measured using Epstein frame method and ring sample method,respectively.The magnetization curve and loss curve of the material were obtained,which provided the material property parameters for magnetic field simulation.Then,to provide the heat source for heat-flow coupling calculation,the three-dimensional main magnetic field and leakage magnetic field simulation calculation in the transformer were carried out by using Maxwell commercial finite element calculation software.The magnetic field and loss distribution in the transformer core,clamp,magnetic shield,oil tank and winding were given.The influences of magnetic shield on the magnetic field distribution and loss in the transformer were discussed,which provided a reference for the structure optimization design of traction transformers.Finally,the three-dimensional temperature field and flow field were simulated using ANSYS Fluent commercial software.The temperature distribution in each component and oil flow velocity distribution in each region were obtained when the traction transformer ran under the rated state.The influences of magnetic shielding,core loading partition heat source or average heat source,different inlet flow rate,different inlet oil temperature,different inlet and outlet position,and the function of transformer oil physical parameters as constant or temperature on the inner temperature distribution and oil flow velocity in the traction transformer were discussed,which provided an effective simulation method for calculating the oil flow distribution inside the transformer.