PURPOSE: To prevent partial discharge developing from an insulating layer interface and to miniaturize and lighten the weight of a coil by forming a cable terminal at a specified percent or more of the ratio of the height of the cable side ground layer to the insulating height of a ground coil.

CONSTITUTION: Compressing a fixture metal 17 axially develops a void 20 in a vicinity of the end of a ground layer 15 formed out of rubber demarcated by the boundary of a coil side insulating layer projection 8a. However, a range of this void 20 is almost at a constant proportion to the full length l0 of the coil side insulating layer 8 and amounts to several %. This void 20 varies size with the thickness of the ground layer 15: the thinner, the larger; the ratio which does not affect the mutual plane pressures of insulating layers 8-14 is over about 10% in l/l0. Partial discharge due to the void 20 is prevented and causes no deterioration in insulation but can maintain a high insulating performance. Therefore, the insulating distance of the lead zone can be reduced and thickening an insulation more than necessary can be dispensed with, resulting in that the coil 1 can be miniaturized and lightened in weight.