What is the permissible overload percent for dry type transformers?

The rated overloading of a transformer depends on the transformer's previous load, the corresponding windings or oil temperature at the beginning of the overloading.
Examples of the permissible duration and the respective levels of the acceptable over loadings are shown below for dry type transformers according to IEC 60076-12 and for transformer with thermal class 155°C (F).
For example, if the transformer is loaded with 50% of its rated power continuously, then the transformer can be overloaded to 150% or to 120%, only the time will be the difference.

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