A generator having a rotor which comprises rotor excitation element-carrying modules, for example magnets, radially movable in relation to the generator shaft in such a manner, when in their retracted position, as to significantly ease generator transport and assembly. The use of these movable magnet-carrying modules is particularly useful in direct drive-type generators which do not require a multiplier. Another object of the invention is an assembly process which comprises a generator equipped with the radially movable magnet-carrying modules.