Oil-cooled Transformer Thermal Calculations

In order to determine how to improve the thermal characteristics of a transformer, Flometrics was hired to evaluate where the largest temperature differences were. We determined that the largest temperature drop was within the windings of the transformers, and we also determined the optimum gap in the oil between the transformer and the case. A gap which is too small will inhibit natural convection and make the transformer run too hot:

In order to do this calculation, you have to assume a value for the temperature and then calculate the heat transfer rate and make sure that the rate matches the actual rate.