Numerical Calculation And Analysis Of Temperature Field Of Oil-Immersed Transformer

Transformer is an important equipment in power system, it is very significant to the power economical transmission, flexible distribution and safely use. At present, one of the important and difficult problems which need resolve is the energy saving and overheating control of power transformer, and it is significant to ensure long-term safe operation of power system. So accurate calculation and reasonable controlling distribution of average temperature rise and hot-spot temperature of transformer that meet the standard requirement are critical to ensure transformer to run safely, economically and high-effectively. It can be proved by experiment that the larger of the capacity of transformer, the bigger of the corresponding ratio of leakage magnetic to primary magnetic, and the exaggeration of loss is likely to produce the superheating problem of the coil. When the temperature of the coil reaches one grade, it must be overstepped the limit value of temperature rise which provided for by the state. Moreover the limit value of temperature rise is on the basis of the useful life of transformer.The thesis basic on the status of research for transformer temperature field calculation both at home and abroad, stand on the application of engineering practices, the principle of heat transmission, the classic experimental standard of heat exchange and the study of principle of heat-cool to analysis internal heat source and heat dissipation mode and summarize the solving formula of average thermal conductivity of the pancake windings and convection heat transfer coefficient of tank outer surface. Three-dimensional temperature field and oil flow field of forced oil circulation transformer and natural oil circulation transformer are analyzed by large finite element software FLUENT. First, temperature field and oil flow field distribution of every components on 17000 kVA /37.6kV forced oil circulation transformer are calculated, and the simulation results and experiment results are compared, the causes of error are concluded, the accuracy of the calculation method is verified, on this basis, influence of magnetic shields on temperature field of tank surface and inlet oil velocity on temperature field of transformer; Secondly, temperature field on 10000 kVA /35kV natural oil circulation transformer is calculated by Boussinesq model of FLUENT software, three-dimensional model of transformer that the winding is pancake is built, the complicated pancake and parallel duct are meshed using the method of from down to up layered cut into parts by GAMBIT, the quality of grids are guaranteed and the accuracy of calculation is improved, the simulation results and analytic results are compared, the relative error is estimated below 10%; Finally, two-dimensional temperature field model of natural oil circulation transformer is built, the two-dimensional results basically tallies three-dimensional results, on that basis, influence of the parallel duct height, the number of blockwashers, the comparison of heat center and thermal center and load coefficient on winding average temperature rise and hot-point temperature rise were analyzed using two-dimensional model and the conclusion are given out, which has certain guiding significance for the structure design of transformer.