Abstract: A wedge for an electrical machine core includes a hollow wedge body including a wedge wall extending in an axial direction. The wedge wall separates an interior hollow space of the wedge body from a space exterior to the wedge body. A phase change material can be housed within the interior hollow space of the wedge for regulating heat transfer through the wedge. An electrical machine includes a wound rotor including an electrical steel core and a plurality of wedges mounted to the electrical steel core with electrical machine windings retained between each wedge and the core body. Each of the wedges includes a hollow wedge body as described above.