Multi-field Coupling Calculation Method And Casting Structure Research Of Dry-type On-board Traction Transformer

As the core electrical equipment of EMUs,the internal temperature rise characteristics of the on-board traction transformers greatly affect the operational reliability of the EMU.Current on-board traction transformers of EMUs all adopt oil-immersed cooling and insulating structures,and the tons of insulating oil limits the efficiency of the EMU and has potential fire hazards.The dry-type on-board transformer with resin cast insulation and train induced wind cooling by the relative motion of train and air can eliminate the insulating oil and its affiliated parts to achieve light weight and improve EMU’s safety and reliability,but its cooling way and structure have changed significantly,and it is affected by multiple factors that are unfavorable to its heat dissipation,such as compact working space and long-term working conditions with frequent load fluctuations.Therefore,it is important to accurately calculate the temperature rise characteristics of dry-type on-board transformers and obtain the load characteristics under different working conditions for their thermal design and casting structure optimization,so the following studies are carried out in this paper:Firstly,a multi-field coupled numerical model of dry-type on-board transformer is established to analyze its overall leakage magnetic distribution and load loss under rated operating conditions,and then coupled loss to the fluid-temperature field for accurate calculation of its temperature rise distribution,and the mentioned numerical modeling calculation method’s validity and accuracy are verified by the experimental platform.On this basis,the overall winding temperature rise distribution law of dry-type on-board transformer leakage magnetic field with counted and winding eddy current losses is revealed,and it is compared and analyzed with the traditional calculation method of winding load loss averaging.Secondly,a united simulation model of the traction network and EMU verified by the actual running experiment is established and used as the basis to simulate the load current of dry-type on-board transformers running for a certain period of time under different operating conditions,to provide load excitation for the subsequent multi-field coupled transient hot-spot temperature calculation,and then clarify the variation law of transient hot-spot temperature of dry-type on-board transformers running with the EMU,so as to provide a basis for its reasonable thermal design and optimization of casting structure.This will establish the foundation for reasonable thermal design and optimization of the casting structure.Finally,based on the proposed multi-field coupled temperature rise calculation method,the transient hot-spot temperature of dry-type on-board transformer is calculated under various casting air-duct widths by combining the load current characteristics under different operating conditions.Based on the hot-spot temperature,the sensitivity analysis of the casting air-duct width is carried out to determine the optimization range;the transient hot-spot temperature of the air-duct width within the optimized range is calculated under different operating conditions and load currents,and the variation law of the hot-spot temperature with the air-duct width is investigated,and finally the casting air-duct width parameter that takes into account the transient hot-spot temperature and economy is selected by the TOPSIS-RSR method.