23 January 2021
Ventilation and cooling is an important issue in the installation and operation of transformers
Applies to all Low Voltage (LV) Transformers by SquareD/Schneider Electric
Excessive heat is destructive to transformers
The average ambient temperature for a transformer over a 24 hour period should not exceed 30 degrees Celsius. For instance, if the transformer ambient temperature was 40 deg. C for 12 hours, then the transformer must not exceed 20 deg. C for the remaining 12 hours to average a 30 deg. ambient temperature.
If the average ambient temperature exceeds 30 degrees Celsius, the derating factor is 0.4% reduction of VA for every degree Celsius above 30 degrees Celsius per IEEE C57 12.96. The IEEE formula that is used to derive the 0.4% factor is valid only up to an AVERAGE of 50 degrees Celsius. Also, using transformers above their listed ambient temperature can shorten the life of the transformer. Due to the number of other factors involved, such as loading, frequency of use, and humidity, no data exists on how high ambient temperatures affect the life of a transformer.