Abstract: A condenser (28) is connected at the top (31) to a riser (22) and at the bottom (32) to a downpipe (23). Below the condenser (28), a vertically disposed, plate-shaped element (13) is arranged, there being formed along the two vertical edges of this element the conduits (22, 23) and, between these, several evaporators (15), separated from one another by perforations (17), for transferring the heat loss of the electrical elements to a liquid. Each of the evaporators (15) is connected at one end at the top (18) with the riser (22) and at the opposite end (19) at the bottom with the downpipe (23). The condenser (28), the conduits (22, 23), and the evaporators (15) constitute a unit sealed in a pressure-proof fashion which is filled with the liquid, that can be evaporated in the evaporators (15) by the heat loss and can be condensed in the condenser (28), to such an extent that the liquid volume lies above the uppermost evaporator (15) and below the condenser (28) or in the lower portion of the latter.