Experimental study on the large power transformer unit temperature variation

The monitoring systems of the transformer units are developed according to their loading guides, as their manufacturers specify. The problem that arises is due to the fact that the thermal models of the diverse versions of the loading guides do not yield similar results. Therefore, different values may be obtained for the same transformer unit with different monitoring systems. That is why the values provided by these systems and the standard thermal model should be compared. Another aspect, as important as the previous one; refers to the thermal model parameters that should be specified by the transformer unit manufacturers. The paper presents a mobile installation that was developed to perform these measurements and the results obtained on two 200 MVA power transformer units.