New preventive measures against stray field of heavy current carrying conductors

The stray field of heavy current carrying conductors (HCCC) in large power transformers shows marked differences as compared to that of windings. New types of measures, separated magnetic steel plates welded on a nonmagnetic steel plate and closed loop shield, are presented to reduce the eddy current losses and to prevent the tank cover and walls from local overheating due to HCCC. Furthermore, the influences on the bolts and bushings are discussed. The BEM and FEM are employed to analyze the three dimensional eddy current field. Both numerical and experimental results show that no local overheating appears even if the phase current is up to 16 kA.