A high-voltage transformer for providing an alternating voltage in the kV range, comprising at least one secondary winding wound on a coil carrying body surrounding a transformer core, and an insulation housing encapsulating the secondary winding is provided to electrically insulate the secondary winding. Said insulation housing is walled by the coil carrying body carrying the secondary winding and by an enveloping body made of plastic and enveloping the secondary winding so that an annular gap is formed, wherein the annular gap between the secondary winding and the enveloping body is filled with an insulating fluid. The annular gap has a gap width of less than or equal to 20 mm viewed in the cross-section, and the enveloping body has a wall thickness of less than or equal to 20 mm, wherein the plastic is polypropylene, and a separate expansion volume is not provided for the insulating fluid.