The separation element of the rotor assembly according to the invention preferably has a fluid-guiding portion, which extends through the first shaft portion as far as an axial position between the end faces of the rotor core and partially forms the second shaft portion. The second shaft portion consequently can comprise the interior of the shaft as far as the axial position and the portion of the shaft delimited by an inner wall of the fluid-guiding portion. The first shaft portion can comprise the portion of the shaft delimited by the separation portion and the portion of the shaft delimited by an outer wall of the fluid-guiding portion. The fluid-guiding portion is expediently arranged coaxially with respect to the shaft. The fluid-guiding portion typically leads into the separation element. The fluid-guiding portion is generally formed by a pipe.

In the rotor assembly according to the invention there is particularly preferably also provided a connection element, relative to which the shaft is rotatable, wherein a free end of the shaft associated with the first shaft portion leads into the connection element and is fluidically connected to a feed channel of the connection element. A particularly simple end-side feed of the first shaft portion is thus realised. The connection element typically has a radial shaft ring seal, in which the shaft is rotatable.

The fluid-guiding portion particularly preferably leads into the connection element and is fluidically connected to a further feed channel. The connection element consequently provides both a feed and a return for the cooling fluid and thus makes it possible to provide a particularly simple feed of the shaft at just one free end.