Effective Cooling of a Distribution Transformer Using Biodegradable Oils at Different Climate Conditions

Nowadays, as an alternative to conventional mineral oils used for cooling in distribution transformers, environment-friendly ester oils are getting more attention. For this reason, the main objective of this work was to compare the cooling efficiency of both types of coolants in the medium-power distribution transformer under different ambient conditions. It was conducted by the development of a validated coupled numerical model that included all thermal, flow, and electromagnetic phenomena. Moreover, all the calculations were carried out for mineral, synthetic, and natural ester oils. As a result, the coupled computational fluid dynamics (CFD) model determined the hot-spot temperature within the transformer tank at three ambient temperatures on the basis of the local distribution of the power losses in windings and core that were delivered from the electromagnetic submodel. The investigated ambient temperatures of-10 degrees C, 20 degrees C, and 30 degrees C represented summertime and wintertime for two climate conditions. The numerical results also showed a satisfactory agreement with the measured temperature values recorded in the analyzed distribution transformer with mineral oil. In addition, it was presented that the highest hot-spot temperature of 94.6 degrees C was reached for the case of natural ester oil at 30 degrees C of the ambient temperature representing maximum monthly averaged Argentinian climate conditions. In these conditions, the hot-spot temperature transformer with mineral oil was only 1.6 K lower. Furthermore, one of the investigated synthetic ester oils allowed to reach even better cooling effectiveness than in the case of mineral oil. Therefore, more effective cooling connected with environment-friendly characteristics encourages to use of biodegradable oils for distribution transformers.