Abstract: To reduce the ohmic losses in a sheet-wound transformer or reactor winding, edge regions of at least some of the turns of the conductor sheet forming the winding are located at a different distance from the geometric axis of the winding compared with the distance from said axis of a central conductor portion in a respective one of said turns. Preferably the conductor sheet in each turn substantially follows the flux lines for the resultant magnetic leakage flux which corresponds to a constant current density in the sheet. For example, the winding may be wound from a metallic foil whose edge regions are folded back on themselves, or end regions of the winding may be provided with inter-turn packings (e.g. of tape) to achieve the desired flared shape of the turns at the ends of the winding.