A wound rotor (1) has a structure defining a circumferential alternation of teeth and grooves. The teeth respectively receives longitudinal windings. The rotor (1) has longitudinal ends (17, 17′) and the windings defining, at the longitudinal ends of the rotor (1), protruding coil heads (40). A collar (10, 10′) for mechanically holding the windings is installed at one of the longitudinal ends (17, 17′) of the rotor (1) so as to define a central opening (101, 101′). A nozzle (21, 21′) projects a liquid coolant through the central opening (101, 101′) onto the coil head (40). The collar (10, 10′) has an escape duct (11, 11′) allowing escape of the liquid coolant projected onto the coil heads (40) to an outside of the collar (10, 10′). A longitudinal end of the collar (10, 10′) has a constant reduction in an outer diameter.