If you mean maximum TCL and MD then it may depend on the ownership and operating guidelines, or it may depend on codes.
For a utility owned transformer the maximum demand may depend on the duration of the overload and the maximum allowable voltage dip. Loading above 100% leads to poorer voltage regulation and reduced transformer life.
If the transformer is subject to electrical codes then some codes require that the continuously connected load may not exceed 100% of the transformer rating and the maximum demand may not exceed 100% of the transformer rating. Under some conditions the maximums may be 80% of the ratings.
In North America most customer owned transformers are subject to the electrical codes.
Bill
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"Why not the best?"
Jimmy Carter
