From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Explaining the theory of action of the 'Smith' constant current dynamo.
| Identifier | ExFiles\Box 3\5\ 05-page082 | |
| Date | 30th July 1919 guessed | |
| (I) X. 295 "SMITH" THEORY OF ACTION OF THE [REDACTED] CONSTANT CURRENT DYNAMO. ---ooooooooooooooooo--- The conditions at no load, when the machine is only supplying its own field current are shown in Fig.I. The conditions are exactly similar to an ordinary Dynamo, with the addition of the auxiliary brushes and resistances. Current flows through the resistances as shown. The directions of the F.M.F's in the four sections of the winding are shown by red arrows, and the currents by black arrows. When load is placed on the machine, the effect of Armature reaction sweeps the flux in the direction of rotation, exactly as in an ordinary Dynamo. This means that the sections, A.D & B.C., of the winding cut more flux than normal, and the sections A.B. & C.D, less. The voltage between the brushes, A & D, and B & C is therefore increased, and that between A & B and C & D reduced. Thus the currents through the resistances decrease. If the speed of the machine now increases, the voltage rises and the current increases. This has the effect of further distorting the field, until flux from the N.Pole cutting the end of section CD, only generates an EMF sufficient to keep the current flowing through the winding, that is E.M.F. generated = drop in cd, and is in same direction. There is no E.M.F. between the brushes C and D, and thus no current flows through the resistance. The same action takes place in section AB. The conditions are then as shown, in FIG.2. | ||