A power transformer comprising at least one high voltage winding (32) and one low voltage winding (30). Each of the windings includes at least one current-carrying conductor, a first layer having semi-conducting properties provided around said conductor, a solid insulating layer provided around said first layer, and a second layer having semi-conducting properties provided around said insulating layer. The windings are intermixed such that turns of the high voltage winding are mixed with turns of the low voltage winding.