Abstract: In a three-phase and three-leg core structure of a core-type transformer comprising three main legs of a substantially circular cross-sectional shape and a yoke of a non-circular cross-sectional shape for magnetically connecting the three main legs, each of the three main legs having a cross-sectional area substantially equal to the cross-sectional area of the yoke, wherein at least joints between the steel plate laminations of a center main leg and the adjoining steel plate laminations of the yoke are in a mitered oblique joint without requiring the shearing of the ends of the steel plate laminations, and the edges of the leg and yoke laminations at which edges the oblique miter joints are formed approach each other in length.

Abstract: A single-phase three-legged core for a core type transformer in which a plurality of steel sheets constituting each layer of laminations of a main leg are jointed at their diagonally cut sides to corresponding sides of a plurality of steel sheets constituting each layer of laminations of yokes to form a plurality of joints. At the inner corner portion of each joint, a recess is provided along the main leg or yoke steel sheet having a greater width than the other, so that a plurality of main leg laminations having stepwise varying width can be jointed to a plurality of yoke laminations at the same joint angle in the area of the recesses thereby simplifying the step of sheet cutting. At the outer corner portion of some of the joints, the vertex of the diagonally cut side of the corresponding main leg steel sheet mates with that of the associated yoke steel sheet to provide an outer corner joint, so that magnetic flux can uniformly pass through the joints to minimize the core loss.