Transformer Winding Hot Spot Temperature Determination
Loading capability of power transformers is limited mainly by winding temperature.
As part of acceptance tests on new units, the temperature rise test is intended to demonstrate that, at full load and rated ambient temperature, the average winding temperature will not exceed the limits set by industry standards. However the temperature of the winding is not uniform and the real limiting factor is actually the hottest section of the winding commonly called winding hot spot.
This hot spot area is located somewhere toward the top of the transformer, and not accessible for direct measurement with conventional methods.