A transformer includes a first winding arranged around an axis, and a second winding arranged around the axis. The second winding includes a litz wire having an end portion located at an axial end position of the second winding and a middle portion located at an axial middle position of the second winding. The litz wire has a first cross section at the end portion and a second cross section at the middle portion, the cross sections each including in a quadrant between the axial outward direction and the direction pointing towards the first winding a curvature extending between the axial outward direction and the direction pointing towards the first winding. The curvature of the first cross section is smaller than the curvature of the second cross section thereby reducing the peak magnitude of the electrical field between the end portion of the second winding and the first winding.