Research Of Large Oil Immersed Self Cooled Transformer Temperature Rise

The oil-immersed transformer has advantages of high voltage grade, excellent heat dissipation, low loss, large capacity, low price and so on. Most of power transformers operating currently on the power grid are oil-immersed transformers, of which 80% use cooling method of ONAN. Now days the large power transformer also adopt ONAN cooling methods in order to solve the problems such as big noise, oil-flow electrification phenomenon and so on.The cooling method of ONAN will increase temperature difference between copper windings and insulation oil, thus the transformer’s thermal dissipation becomes a more prominent problem. The engineering calculation method of temperature rise for the oil-immersed power transformer, which is just empirical formula, that is adopted by transformer manufacturer can not show the real temperature rise and may have large deviation sometimes.This literature summarize a precise calculation method of average oil temperature rise, top oil temperature rise and winding temperature rise for large power transformer with ONAN cooling and winding guide structure by analyzing and researching on the theory of transformer’s heating and cooling, according to basic principle of heat transfer theory. It then analyze some main factors that affect transformer temperature rise, such as total loss, the location of radiator and structure of windings. Finally it compares the temperature rise result with a certain transformer SSZ10-ZN-240000/220 with optical fiber temperature detection, which is produced by Sanbian Sci-Tech Co.,Ltd. The Calculation values and experimental values are very close, so this calculation method can be put in engineering use.