Numerical Simulation Research On Temperature Fields In S11-2000/10/0.4 Oil-immersed Transformer

In recent years, more and more electric cars are beginning to connect to the electricity grid with its rapid development. And a large number of electric vehicle charging can cause electricity load to increase dramatically, it may make some transformer run under full load condition for a long time and lead to overtemperature phenomenon. Small and medium sized transformer can meet the demand of charging pile which input voltage is 220v/380 v alternating current. Therefore, the charging station may temporarily put some small or medium-sized oil-immersed transformer to ensure the safe operation of transformer. But the small or medium-sized oil-immersed transformer may can’t heat dissipation timely and lead to the transformer overtemperature in the process of start, it is necessary for the study of the transformer transient temperature field to guarantee its safe operation.This article take S11-2000/10/0.4 type transformer as the research object, set up the natural oil circulation transformer model by simplifying its internal structure model rationally. And the corresponding forced oil circulating transformer model is set up by modifying the transformer tank. The transient temperature field in natural and forced oil circulating transformer is analyzed by COMSOL on the basis of theoretical analysis of transformer thermal performance. The influence of different time and fuel tank wall temperature is discussed on temperature field and hot spot in transformer, and the influence of inlet oil rate is also discussed for the forced oil circulating transformer. The transient temperature field and hot spot in the natural and forced oil circulating transformer is compared under the same flow(about 1.67×10-3m3/s).Studies have shown that both natural and forced oil circulating transformers’ high temperature are concentrated in the region of the upper winding core, and the transient process time respectively is 180 min and 30 min. The transformer temperature field and hot spot increase with the increase of transient process time and the oil tank outer wall temperature, and with the increase of the oil tank outer wall temperature in linear relationship. In the forced oil circulating transformer, its temperature field and hot spot are decreased with the increase of the inlet oil rate and the trend of reducing gradually slow down, so the velocity of inlet oil exists an optimum value. The transformer hot spot is located in the upper of middle low voltage winding, the hot spot height in the natural oil circulation transformer range 639 mm to 740 mm and the maximum is 367 K; the hot spot height in the forced oil circulation transformer(the oil tank outer wall temperature is 313.15 K) range 594 mm to 724 mm and the maximum is 354 K. For the same flow rate(about 1.67×10-3m3/s) natural oil circulation and forced oil circulating transformer, the latter cooling effect is much better than the former and the forced hot oil circulation height range 577 mm to 613 mm which is lower than the natural oil circulation. The maximum of hot spot respectively is 367 K and 332 K, both of the hot spots are less than the allowable value and the transformers can ensure safe operation.