GB597882A - Improvements in or relating to rotating electrical machinery - Google Patents

Abstract

597,882. A.C. generators. ARNOT, A. R. E. Oct. 21, 1944, Nos. 20438/44 and 11547/45. [Classes 35 and 38 (iv)] A governed frequency polyphase alternator has its rotor excited from polyphase rotating brushes on the exciter commutator, the brushes rotating at a speed proportional to any speed variation between the alternator rotor and a governing motor. In one form, the rotor 12 of alternator 11 is fed through slip-rings 14, 15, 16 and 32, 33, 34 from rotary brushes 27, 28, 29 on the commutator of the exciter 20 which derives its own excitation from brushes 25, 26. A differential gear drives the brush carrier 30 at the speed difference between the alternator shaft 13 and the constant speed governing motor 46. In a modification, Fig. 2 (not shown), the differential gear is replaced by a synchronous motor, one member of which is driven by the alternator shaft and whose other member which drives the rotary brush-gear is energized by a constant frequency supply. In a further form, Fig. 5 (also not shown), the exciter is replaced by a commutator connected to the alternator stator winding, the brushgear being driven and supplying the rotor as before. The governing motor now runs at twice the output frequency. In some cases, to avoid sparking, a pressure casing may be used or two commutators may be employed having alternate tappings from the armature and the brushes connected through currentlimiting devices. When driven by an A.C. motor, the whole machine acts as a frequency changer.