In this paper, a new approach to calculate stray loss in power transformer is presented. Three-dimensional Finite Element Method (FEM) is widely used to calculate a local overheating in consequence of the loss. However, there are limits to use three-dimensional (3D) FEM in the beginning of design process due to its calculation time and the absence of 3D model. And it is difficult to apply two-dimensional (2D) FEM or axi-symmetric method for electromagnetic calculation of high voltage transformer because rectangular shaped tank wall and cylindrical winding core should be solved simultaneously. In order to overcome the difficulties of usage of 2D/3D FE calculation, 2D finite element method combined with numerical interpolation is used for leakage flux on the tank wall. And then stray loss is calculated by considering skin depth effect on tank walls. Finally, the loss and calculation time obtained by employing the proposed method are compared with 3D calculation results. From this result, it is proved that stray loss method in this paper can reduce expensive design modifications before testing.
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