In the design of heavy current transformer

equivalent test is widely conducted to optimize the turns and connections of shielding coils.However

this method is not so accurate

and is of high cost and long period for research.Therefore

a 3D FEM（finite element method） computation of magnetic field for heavy current transformer is presented in this paper.The A-Φ method

which is based on magnetic vector potential and electric scalar potential

is adopted to compute the magnetic fields.And the indirect field-circuit coupling approach is used to consider the effect of external circuits.Considering the interference of stray flux from adjacent bus-bar

the maximal magnetic flux density in iron core and the currents in shielding coils are computed

and their variation with position are determined as well.Consistency of the simulation and theoretical results demonstrates that 3D FEM could be used to compute the magnetic field of heavy current transformer

thereby to replace the high-cost equivalent test.