If you do not change the windings and want to operate at 25 MVA , (a) The load losses will increase by 56 % (b) The voltage drop will be more on the secondary side . This may ceate problem in ,load sharing if the transformer is operating in parallel with other transformers ( c ) The hot spot temperature of winding will go up if there is no enhanvement in the cooling system. The amount will go up depending upon the type of cooling employed . ( d ) The overlaoding of the transformer can not abide the IEC norms (e ) As a side effect the transformer will be ageing faster than expected .