| Lightweight electric traction system is the established development direction of highspeed EMUs in our country.The new dry-type on-board transformer scheme has the advantages of light weight,high safety,and can improve the energy efficiency of EMUs.Ensuring its safe and reliable operation is the premise of practical application.The temperature and the flow distribution of the cooling medium seriously affect the insulation aging degree and life of the transformer.The research on cooling medium distribution and heat dissipation optimization of dry-type on-board transformers can provide more efficient technical means for on-line monitoring,life evaluation and optimal design of dry-type on-board transformers.To this end,the research done in this paper is as follows:First,in order to explore the thermal characteristics of the inner layer windings of the drytype on-board transformer and the distribution characteristics of cooling airflow.For the onboard transformer of the EMU with a rated capacity of 6.3 MVA,the CFD finite element simulation modeling of the temperature field and flow field in the winding area was carried out.The dry-type on-board transformer air-cooled test platform was built to verify the validity and accuracy of the finite element modeling method,and it was clear: the advantages of twodimensional axisymmetric modeling compared with three-dimensional modeling,the distribution law of wind speed in the air duct,the distribution law of the winding temperature,the change of the local flow velocity/temperature in the winding area,the formation of flow characteristics such as "reflow" and "contraction of the flow beam",and the important influence of the wind speed in the air duct on the temperature distribution of the winding;Secondly,aiming at realizing the rapid calculation of the internal temperature and cooling airflow distribution of the dry-type on-board transformer,several groups of finite element simulation data are fitted to obtain the minor loss coefficient correlation,the correlation is suitable for the change of the winding duct geometry and physical parameters of the dry-type on-board transformer.Based on the multi-objective optimization algorithm,the cooling air distribution calculation model is established.The built model greatly improves the computational efficiency.The accuracy of the cooling air distribution calculation model applied to the numerical calculation of winding temperature distribution is verified by the test platform.The built model can provide reference and guidance for the thermal design of the dry-type on-board transformer winding area;Finally,aiming at the problem of heat dissipation found in the above research,a squaresheet turbulence structure is proposed to improve the heat transfer performance of the winding air duct by changing the cooling airflow structure.The response surface method is used to analyze the geometric parameters affecting the heat transfer and flow performance of the air duct,and the heat transfer flow correlation formula is established.Then through TOPSIS the optimal geometric parameter combination that considering heat transfer enhancement performance and flow resistance was selected.The 3D printing technology and the dry-type on-board transformer test platform were used to verify the effectiveness of the turbulence structure to enhance the heat transfer performance of the winding cooling air duct. |
