Research On Heat Dissipation System Of Air-Cooling Traction Transformers With Forced Oil Circulation

A traction transformer is the key unit of Electric Multiple Units(EMUs),which provides electrical energy to traction device.The EMUs leave stations with a high acceleration because they run for a short interval between two stops.Thus,the traction device often operates at a high-power working state,and its electrical transformer works at the condition with a large energy dissipation.To avoid internal winding temperature exceeding permissible level,traction transformers must be effectively cooled.Air cooling along with forced oil circulation is a novel and efficient cooling solution for traction transformers,where an oil pump is adopted to transport the oil to the transformer to cool the windings and an oil cooler to release the thermal energy of the heated oil.This thesis intends to study this efficient heat dissipation system of transformer via a combination of numerical simulation and experimental verification.Taking the actual working characteristics of EMUs into account,the author focuses on the rise of winding temperature when the transformer works at a high power.The plate-fin oil cooler,whose oil side and air side adopt serrated and corrugated fins to enhance heat transfer,respectively,is the core component of the traction transformer heat dissipation system.For the thermal and fluid performances of the heat exchanger,an experimental study is conducted and performance calculation model is established after CFD calculations.The main contents of the thesis are as follows:1)This thesis test the traction transformer oil cooler with a wind tunnel test bench.Heat transfer and flow resistance performance under different air and oil flow rates are measured and fitted with the Empirical Correlation.The characteristic data of heat transfer and flow resistance are obtained for both the corrugated and serrated fin channels from the Fluent software.With the data mentioned above,a cooling performance model is established by the logarithmic average temperature difference method.2)The distributed parameter model of transformer(including windings and cooling oil)is obtained with the assumption of one-dimensional temperature field.Then the mathematical model of the heat dissipation system of the air-cooled traction transformer with forced oil circulation is obtained by coupling the distributed parameter model of transformer with the lump parameter model of oil cooler,oil pump and pipeline.Besides,a set of numerical solution algorithms are proposed for the model.3)A traction transformer and its cooling system are experimented for dynamic temperature rise on the experimental platform for transformer temperature rise,and the temperature rises of windings and cooling oil are measured.4)The prediction accuracy of the traction-transformer cooling system model is verified by the experimental data of transformer temperature rise.On this basis,the transformer cooling system model in this thesis is applied to study the temperature distribution inside the windings.The influence of several major parameters on the temperature field of the transformer is analyzed.As the research results show,the numerical model of the traction transformer cooling system in this paper can accurately predict the dynamic temperature changes inside the traction transformer.The transition time and stable value of the cooling oil temperature square with the experimental values.The relative error between the average winding temperature and the experimental value is less than 5%.The plate-fin oil cooler performs excellently.The total heat transfer coefficient based on the surface area of the oil side is 49～74 W/(m~2·℃).This project can be used for designing and optimizing the heat dissipation system of the traction transformer.