The disclosure relates to a transformer coil which can be cooled by a heat pipe and has a primary winding and a secondary winding and relates to a transformer which is formed from transformer coils which can be cooled in this way. The heat from the transformer coil is dissipated by the heat pipe. The evaporator of the heat pipe is arranged in the area of the windings and forms at least one extensive evaporator segment, which extends in the circumferential direction of the windings and along the winding axis of the transformer coil and in the process covers a multiplicity of the turns of the secondary winding.