Transformer Efficency:

Transformer is a static device which transfers the power from one circuit to other through electromagnetic induction. In electrical transformer as there are no moving parts,

 1. no friction and
 2. windage losses occur

 and other losses in transformer are less as magnetic path of a transformer is a closed loop (no air gap exist like induction motor between two circuits). Losses in the transformer are very less compared to any other rotating machine, hence efficiency of transformers will be very high. Efficiency will be of the order of 95% to 98%.