Some Aspects of Temperature Rises in a Natural Cooled Oil-Filled Three-Phase Transformer

Evaluation of transformer overloading capability

“…They present the results of their analyses for winter loading when the temperature changes are quite rapid. [20][21][22][23][24][25][26] Until the early 1970s, the principal factor in determining the thermal rating, and thus the loading capability of transformers, was the average rise of the windings. This temperature rise was determined by measuring the change in winding resistance when the load was applied to the transformer.…”

“…This temperature rise was determined by measuring the change in winding resistance when the load was applied to the transformer. The temperature rise by resistance standard was changed when it was discovered that the hottestspot winding temperature gives a better indication of how the load affects the life expectancy of a transformer [20][21][22][23]. However, the hottest-spot temperature cannot be measured directly because of the hazard of inserting temperature sensors directly into the windings.…”