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).
Analysis of the characteristics of carbon contacts and their effect on field windings and voltage curves.
| Identifier | ExFiles\Box 31\1\ Scan076 | |
| Date | 17th August 1920 | |
| Contd. -3- EFC4/T17.8.20. will be seen from the diagram that when the carbon contacts are completely separated, there is no supply of current to the field winding at all. The carbon contacts introduce a slight amount of resistance, even when no current is passing through the operating coils, and this resistance is increased as the pressure between the contacts is reduced due to currents in the coils. This causes the field to lower than the speed at which the contacts begin to tremble. It results in the characteristic of these contacts that there is really no very definite point at which it can be said that the vibrator begins to operate, as is the case when metallic contacts are used. Above this rather indefinite point the resistance introduced in the field circuit is of the nature of a hot carbon contact with a tendency towards an arc. So far, we have only completed open circuit results which are exhibited on the curves given. These curves show first, the open circuit voltage in the cold and hot conditions when running as a shunt volt machine with the carbon contacts short circuited, and secondly, open circuit voltage curves with the controlled in action. It will be noticed before the vibrator begins to operate, the voltage curve bends away from that for plain shunt owing to the resistance of the contact itself, and afterwards how the voltage curves rise from the points at which the vibrator. Cont'd.{John DeLooze - Company Secretary} | ||