Study On Intensive Cooling Of Electric Traction Unit For EMU

With the improvement of people’s ecological awareness,the carbon emission and noise pollution of electric train units are gradually reduced,which is in line with the current social development trend in China.In the development of electric EMUs,the heat dissipation of electric traction unit is an important research topic.The devices that generate a lot of heat energy in electric traction devices mainly include traction transformers and traction converters.Too high temperature will not only reduce the working efficiency of electric power equipment,but also reduce the service life of electric power equipment.Organic Rankine cycle(ORC)power generation system is a new environmental protection technology which absorbs industrial waste heat,solar energy and other low temperature heat energy by evaporative cooling principle.This method can not only efficiently absorb the heat generated by the electric traction device,but also the heat absorbed can be converted into mechanical energy through the compressor to be recycled.So it will be one of the future development directions to use evaporative cooling in electric traction device.In this paper,the electric traction device of high-speed EMUs is taken as the research object.Evaporative cooling is adopted to absorb the heat generated by traction converters and transformers.Firstly,the development of the cooling technology of traction converters in high-speed EMUs is summarized.Taking the traction converters in CRH EMUs as the simulation and optimization prototype,the cooling substrate structure model of enhanced evaporative heat transfer is designed according to the structural characteristics of IGBT.The CFD simulation method is used to simulate the unit runner test,and the variation trend of simulation results and experimental results is compared and analyzed to verify the reliability of the simulation model in this paper.The effects of different height of ribs and inlet velocity on evaporative heat transfer in reinforced passage are discussed.Then,based on the electrical parameters and material information of the traction transformer of CRH train unit,the windings and the structure size of the iron core are designed according to the design principle of the transformer,and a simple transformer model is built,which is simulated by electromagnetic simulation module of ANSYS software.The core loss and the winding loss are calculated and the distribution of electromagnetic density and core loss in the transformer is discussed.Finally,core loss and winding loss are used as the internal heat source of traction transformer.Based on the gas-liquid changes in the evaporative cooling process,the structure of forced evaporative cooling transformer is designed by changing the positions of inlet and outlet and the cooling working medium on the basis of the structure of ATM9 oil-immersed transformer.The velocity field and temperature field distribution of traction transformer at different inlet velocities were solved by Fluent numerically.Through the research of intensive cooling of electric traction unit of EMU,the heat transfer performance is improved by 5.2% ～ 12.4% when the traction converter base plate is equipped with new rib plate.Both the height of the ribs and the increase of the inlet speed improve the heat transfer performance.Under the influence of bubbles and flow patterns in the passage,the heat transfer effect is best when the height of the ribs is 7 mm and the inlet velocity is 0.6 m/s.Traction transformer adopts forced evaporative cooling structure,and the distribution of thermal and physical field in the box is complicated due to the influence of velocity,flow pattern and gas-liquid mixed flow.Increasing the inlet velocity can reduce the overall temperature in the transformer,but the greater the velocity,the greater the fluctuation of the maximum wall temperature.