The transformer and reactor has a magnetic circuit with a magnetic core and one or more windings. The windings comprise one current carrying conductor and an insulation system. The insulation system has two semiconducting layers, with each layer constituting an equipotential surface. Solid insulation is located between the windings. One of the semiconducting layers has an equal thermal expansion coefficient as the solid insulation. The potential of the inner layer is equal to the conductor potential. The outer layer constitutes an equipotential surface surrounding the conductor. The outer layer is connected to ground potential.
