The hot spot temperature is closely related to the insulation life of transformer and is the most critical limiting factor for transformer loads. Consequently

we established a distributed thermal circuit model of oil-immersed distribution transformers based on the real heat dissipation structure of transformer. In the model

the transformer oil is regarded as the external environment of the windings and the heat dissipation process between the winding layers is mainly focused on.Therefore

both of the temperature and position of the hot spot can be obtained through the model. And the accuracy of the model is verified based on the parameters of the 100 kVA

315 kVA

and 400 kVA pole-mounted transformers. In the rated operating conditions

the difference between model outputs and the measured average temperature rise of the windings obtained through the temperature-rising test report is small

which has proved the accuracy of the model. What is more

the hot spot calculation results of the model are slightly lower than the calculating values of the load guidance method. The comparison results further verify the effectiveness of the model for a certain margin exists in the load guidance method. The model outputs reveal that the temperature of the winding near the core and close to the oil flow is lower than that in the middle layer and the maximum temperature difference between the different layer winding can reach10 ℃ in the rated operating conditions.