Study on eddy current losses and shielding measures in large power transformers

The improved T-Ω method is applied to the computation of the three dimensional eddy current field in a 360 MVA/500 kV large power transformer, the structure of which is complicated. The different cases of tank wall with magnetic shunt, aluminium screen or without any shield are analyzed. The relations between eddy current losses and the materials, structure and size of the tank shield are presented. Compared with a parallel magnetic shunt arrangement, the vertical magnetic shunt reduces stray losses by 63.8%. The optimal thickness of the vertical magnetic shunt is 10 mm. The magnetic shunt should be spread over 0.5 mm at both ends of windings in the 360 MVA/500 kV large power transformer