ANALYSIS OF LEAKAGE MAGNETIC PROBLEMS IN SHELL-FORM POWER TRANSFORMER

The principles of minimized magnetic energy and voltage equilibrium ha ve been combined with the finite element method to solve the leakage m agnetic field problems coupled with an unknown ampere-turn distributio n in the shell-form power transformer. Based on the leakage magnetic f ield calculated, the eddy current and circulating current losses in th e coils are further computed. The calculated results are consistent wi th measured values for a model of a shell-form transformer. Above prin ciples are applied to the windings design of a 50MVA three-phase proto type shell-form power transformer. The calculated results show that th e 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 t hese ends.