The megawatt medium frequency transformer with operating frequency from hundreds to thousands of Hz is a key component of electromagnetic coupling link of large capacity power electronic transformer (PET). The volume of the transformer can be significantly reduced and the power density of the system can be improved by increasing operating frequency of the transformer. However

the medium and high frequency eddy current effect and high current flow can cause the winding loss of the transformer to increase and the efficiency to decrease. The winding form and structure of traditional power frequency transformer

due to the eddy current loss

is not suitable for Megawatt medium transformer any longer. At present

there are few studies on the winding composition and structural form of the Megawatt medium transformer. Based on the frequency characteristics of Megawatt medium frequency transformer windings

in this paper the theoretical calculation methods of different windings are discussed. The electric density distribution and loss of different windings are analyzed

and the copper foil winding is selected as the winding of Megawatt medium frequency transformer. At the same time

the calculation method of the optimal thickness of copper foil winding under the minimum AC resistance is obtaine

and the experimental verification is performed. The experimens show that the calculation and design error of the optimal thickness of copper foil is less than 10% under the trapezoidal and sine wave excitation

and the optimization direction of transformer winding is identified. Finally

a 1.25 MW 600 Hz medium frequency transformer based on copper foil winding is developed

and the efficiency of the transformer is improved to 99.57%.