Transformer Engineering, 2nd Edition

4

Eddy Currents and Winding Stray Losses

The load loss of a transformer consists of the loss due to the ohmic resistance of windings (I²R losses) and some additional losses. These additional losses are generally known as stray losses which occur due to the leakage field of windings and the field of high current carrying leads/bus-bars. The stray losses in the windings are further classified as eddy and circulating current losses. The remaining stray losses occur in structural steel parts. There is always some amount of leakage field in all types of transformers, and in large power transformers, which may be limited in size due to transport and space restrictions, the stray field strength increases with the rating much faster than in small transformers. ...