64 which extend outwardly from core 60 pole 58 terminates in an end portion 66 which has an arcuate outer surface 68 and undersurfaces 70 and 72 ridges 74 and 76 are provided on undersurfaces 70 and 72 respectively rotor 52 differs from rotor 10 in that rotor 52 is provided with shoulders 78 and 80 which extend outwardly from walls 62 and 64 respectively shoulders 78 and 80 each have an upper side 82 and 84 a slot 86 is formed by upper side 82 and undersurface 70 slot 86 opens outwardly from wall 62 a slot 88 is formed by upper side 84 and undersurface 72 slot 88 opens outwardly from wall 64 ridges 74 and 76 extend across the opening of sots 86 and 88 respectively wedge 90 retains main field windings 96 within the recesses between adjacent poles during rotation the wedge has a lip 92 and a lip 94 which are retained in slots 86 and 88 on adjacent poles upper surface 82 of shoulder 78 and upper surface 84 of shoulder 80 support the lower portion of the wedge lips 92 and 94 and minimize the deflection of the wedges due to the bending moment caused by the centrifugal force of rotation ridges 74 and 76 engage lips.