A coil for a transformer assembly is provided. The coil extends circumferentially around a longitudinal axis. The coil comprises a foil winding arrangement and a conductor element. The foil winding arrangement extends circumferentially around the longitudinal axis and has four edge regions. The conductor element covers at least partially at least one of the edge regions of the foil winding arrangement. The conductor element allows for a reduction in an electric field that arises during an operation of the transformer assembly at the edges of the foil winding arrangement. In this manner, a performance improvement in partial discharge tests and lightning impulse tests can be achieved.