Analysis of leakage magnetic problems in shell-form power transformer

The principles of minimized magnetic energy and voltage equilibrium have been combined with the finite element method to solve the leakage magnetic field problems coupled with an unknown ampere-turn distribution in shell-form power transformers. Based on the leakage magnetic field calculated, the eddy current and circulating current losses in the coils are further computed. The calculated results are consistent with measured values for a model of a shell-form power transformer. The above principles are applied to the windings design of a 50 MVA three-phase prototype shell-form power transformer. The calculated results show that the largest circulating current in strands of the low-voltage coils near two ends of each phase winding is greatly reduced to 11% from 98% of the rated current in each strand by placing the copper-shieldings on these ends.