If in a transformer the overloading capacity is not mentioned, is there any thumb rule to determine the overloading capacity? example, a 100MVA transformer can be overloaded up to 105MVA considering 5% overloading as safe.

1) If it is mentioned by the transformer manufacturer that the transformer has overloading capacity of 10%. Does it mean that the current can be increase more by 10% above nominal current?

 

DryType Transformers should never be over loaded. Overloading of a transformer results in excessive temperature. This excessive temperature causes overheating which will result in rapid deterioration of the insulation and cause complete failure of the transformer coils.

 

Panth... if your question is intended just for information, that is, nothing you intend to do in the near future, then I suggest you refer to either the USA ANSI/IEEE Xfmr Standard, C57 or your country's own standard. They contain Charts and Tables covering short-time, recurring, overloads for oil-immersed xfmrs!

If you actually intend to do it, then I urge you to contact the manufacture of the xfmr!

If you want a Rule-of-Thumb (ROT),for discussion purposes, then its capacity can be increased 1% for each deg C below what is given as the rated ambient temperature on its nameplate!

Regards, Phil Corso