An experimental determination of the optimum cooling model for dry-type transformers for different cooling configurations

Dry-type transformers are superior in terms of safety and environmental protection compared to oil-filled transformers due to their insulating material. Therefore, these transformers are widely used in many critical applications, such as hospitals, schools, shipping, airports, dams, and renewable energy power plants. However, the heat performance of these transformers is relatively poor because of the low thermal conductivity of the epoxy resin material they use that surrounds the core and coil. In addition, electrical losses increase with the rising power capacity of the transformer, so the losses cause overheating in the transformer core and windings. This situation results in thermal aging and insulation deterioration that reduces the service lifetime of the transformers. Thus, thermal analysis and effective cooling systems for the transformers are significant issues in order to increase the life of the transformers. In this study, a 250 VA 380/110 V three-phase, dry-type transformer was modeled and thermally analyzed using the ANSYS/Fluent program. The transformer was also tested under load conditions so that the thermal behavior of the transformer could be observed via a thermal imaging camera. In order to decrease the temperature rise in the transformer core and windings, different cooling configurations were tried by creating a cooling cabinet. The optimum cooling model was determined thanks to experimental studies. This model was also verified by simulation results. In dry-type transformers, the part where the temperature increases the most is the middle leg of the core and coils. Therefore, the air input through the middle leg of the core and the air output through the side legs of the core provide the greatest cooling of the transformer. This configuration results in the middle leg temperature of the core varying between 35 degrees C and 42 degrees C. In all other fan cooling cases, it is seen in both experimental and simulation results that the temperature values do not drop below 47 degrees C. This study showed that the reliability, insulation, and service life of the dry-type transformer can be improved.