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Grain-oriented (GO) silicon steel laminations are widely used in iron cores and shielding structures of power equipments. When the leakage magnetic flux is very strong and enters the lamination plane perpendicularly, the eddy current loss induced there must be taken into account in electromagnetic design. It is preferable to accurately compute three-dimensional (3-D) eddy currents at least in a few outer sheets of the lamination stack. Since the coating film applied to each sheet is only 2-5 thick, finite element modeling of 3-D eddy currents is very difficult in GO silicon steel laminations of large electromagnetic devices. This paper proposes an inner-constrained separation technique (ICST) to compute the 3-D eddy currents. Instead of the coating film, the ICST introduces an inner constraint into the A-formulation to separate the laminations from each other. By the ICST, the 3-D eddy currents can be computed accurately without meshing the coating film. Numerical experiments are carried out on the TEAM (Testing Electromagnetic Analysis Methods) benchmark model P21c-M1 and the numerical results show good agreement with the measured data.