Multi-physics field simulation of oil-immersed transformers accounting for ambient temperature and load variations

Among the internal faults of transformers, the overheating fault accounts for 45%, which seriously threatens the safe operation of transformers. In order to study the influence of ambient temperature and dynamic load conditions on the transformer hot spot temperature, this paper establishes a three-dimensional magnetic-thermal-current multi-physical field simulation model based on S11-2000/10/0.4 oil-immersed transformer to analyze the transformer hot spot temperature change rule. In the simulation process, the influence of temperature on material properties is considered to accurately simulate the variation of transformer hot spot temperature. The results show that the effect of ambient temperature on the hot spot temperature of the transformer is not linear, and that the change in hot spot temperature is influenced by the two-way coupling between the surface temperature of the oil tank and the ambient temperature; the hot spot temperature and the load factor are positively correlated, and the rate of change of hot spot temperature increases with the increase of the load factor. On the basis of normal periodic daily load and long-term dynamic load considering seasonal load growth, the hot spot temperature of transformer meets the trend of descending, ascending and descending. Comparing the simulation results of two load conditions at the same time, the maximum difference of hot spot temperature can reach 37.1K; Considering the combined effect of load factor and ambient temperature, the change trend of hot spot temperature is the same as that under the separate action of both, but compared with the hot spot temperature under the separate action of seasonal dynamic daily load curve, under the joint action, the difference of hot spot temperature in winter and summer can reach 58.8K, which accelerates the insulation aging of transformer. The research results will provide reference for the design of large oil-immersed transformers in the future.