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).
Page describing the armature reaction and self-regulating characteristics of a machine under varying speed and load.
| Identifier | ExFiles\Box 3\5\ 05-page009 | |
| Date | 1st October 1911 guessed | |
| As the speed increases the machine begins to supply current to the line, and an armature reaction is set up which displaces the axis of the field forward which has the effect of reducing the current in the resistances R and R'. When the axis of the magnetic field is displaced by 45° there will be no current at all between the main and auxiliary brushes as they will be at equal potentials. The reader is here referred to the curves shown in Fig. II, which give (a) the output to the line and (b) the current flowing in resistances R and R'. These curves have been taken from an actual bench test and represent the principal characteristics of the machine. As the load and speed increases the further displacement of the magnetic field causes a current to flow again between the main and auxiliary brushes but now in a reverse direction, with the result that the magnetic field will be weakened and the machine becomes self-regulating. It will be noticed that the currents which now flow in the resistances are in the same direction as the main current, so that the auxiliary brushes at high speeds actually supply part of the main current, and by suitably designing the machine about half of the full load current is supplied by the auxiliary brushes. At full load the armature coils between the main and auxiliary brushes are practically idle and the watts 4 | ||