PURPOSE: To enable to secure the dielectric strength at the flow out aperture part of insulating oil of a disc winding and the lead out aperture part of a high-tension lead wire by a method wherein insulation is reinforced in such a manner that the region ranging from the point in the vicinity of the press-plate of the high-tension lead wire led out through the aperture part of the press-plate to the point located near the aperture part of an electrostatic shield is covered by an insulating pipe.

CONSTITUTION: The upper aperture part located between insulating pipes 1 and 2 on the inside and outside of a disc winding are blocked using electrostatic shields 8 and 9 and insulating barriers 10, 11 and 12 excluding the aperture part 7 in the center part. The insulating oil which has been flown cooling each winding unit 3 of the disc winding flows out to outside through the aperture part 7. The outer circumferential part, ranging from the point located in the vicinity of the aperture part 14 of a press-plate 13 on the high-tension lead wire 15 connected to the tip winding unit 3a to the point in the vicinity of the center aperture part 7 of the electrostatic shields 8 and 9, is covered by the insulating pipe 16 consisting of a pressboard. As a result, the percentage of potential allotment of the insulating pipe 16 is increased, the percentage of potential allotment of the internal part high-tension lead wire 15 is reduced, and a high electric field is eliminated, thereby enabling to accomplish an insulating constitution having no weak point part.