The wires forming the statorand armature windings are held in position, in a manner known per se, by plates 64, 66 of insulating material, such as bakelite, which are slid lengthwise into the slots 41, 56 and are held in position by inward radial pressure of the windings to causethe plates to bear against sideward extensions 60a of teeth 60.The generator is a heteropolar machine which operates in