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).
Description of the electrical currents and forces within a dynamo and armature system during startup.
| Identifier | ExFiles\Box 3\5\ 05-page095 | |
| Date | 13th August 1919 | |
| Contd. -2- EFC1/T13.8.19. During the period between starting up and the point at which the dynamo was connected to the battery by the cut-out, a P.D. increasing with the speed, was generated between the main brushes which caused an exciting current to flow in the field circuit. At the same time E.M.F's were generated in the local circuits from M - to A - and from A + to M + through the armature, causing other currents to flow through these sections of the armature, and back through the resistances R.{Sir Henry Royce} In spite of the symmetrical arrangement of the brushes these E.M.F's would be somewhat smaller than the E.M.F. generated in the armature from A - to M + and from M - to A +, owing to the crowding of the lines of magnetic flux from each main pole towards the trailing edge of that pole, due to the armature currents. They would, however, be large enough to cause considerable flows of current through their corresponding sections of the armature, the actual magnitude of these flows depending, of course, upon the magnitude of the resistances R.{Sir Henry Royce} There would be a most suitable value for these resistances, with the brushes in this position, for general alround results. The currents in the two resistances returning in their corresponding portions of the armature produce a magnetising force in the armature which has a component in the direction of the main flux, and assists in the building up of the voltage in the early stages. Both the field current and the auxiliary currents, also the main voltage, rise in value until the cut-in takes place, and would continue to rise with increase of speed if the battery were not connected (see curves B). When, Contd. | ||