Transformer having passive cooling topology

A passive cooling topology and a manufacturing method are described for a transformer to achieve improved power density at a light weight. No fans or cooling liquids are required. Vertical planar faces are used for the central core element, the primary and secondary windings, the outer core element, and a finned heat sink. The primary flow for thermal cooling is radial, through the vertical planar faces. The transformer may be configured to float at the potential of a high voltage transmission line, leading to improved thermal characteristics. Eddy currents are reduced using repeating air gaps in the central core, and a continuously transposed cable comprising multiple strands per turn in the secondary winding. Air pockets in the windings are eliminated using a potting resin and vacuum pressure impregnation (VPI).