Study on Fast Calculation Model of Hot Spot Temperature of Distribution Transformer Considering Temperature Coupling between Windings

When the three-phase loads of distribution transformer are unbalanced, the temperatures of the windings are different. It leads to the affected heat dissipation process between the windings of adjacent phases. However, the traditional fast calculation model of hot spot temperature for transformer only consider balanced loads ignoring the effect of the temperature coupling between inter-phase windings. In this paper, a multiphysics field simulation is used to study the temperature distribution inside a distribution transformer under different unbalanced working conditions, And the temperature coupling between inter-phase windings is analyzed. There is a compound heat transfer process, consisted of radiation, convection and convection heat transfers, between adjacent two-phase windings. After that, a three-phase thermal circuit model considering the temperature coupling between windings is established based on the thermoelectric analogy theory. And the typical parameters within the thermal elements as well as the coupling thermal resistance between windings are proposed. By using the model, the hot spot temperature of the distribution transformer under the unbalanced load operating condition can be calculated precisely. Compared to the traditional model, the maximum error of the modified thermal circuit model is reduced from -4.1℃ to -1.3℃.