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).
Technical explanation of the characteristics of an external electrical circuit and a shunt wound generator.
| Identifier | ExFiles\Box 61\2\ scan0214 | |
| Date | 12th December 1925 guessed | |
| -2- contd. In a similar way an external circuit containing a back E.M.F. in addition to a pure resistance has a character-istic represented by some such line as K, showing a voltage when there is no current, added to which there is a rise of voltage proportional to the current. Now, if we superpose the volt-ampere characteristic of the external circuit and the volt-ampere characteristic of the generator, a point of intersection such as Q or R is the only point which satisfies both generator and external circuit and must give the volts and amperes at the working condition. Knowing therefore the family of output characteristics of a shunt wound generator for various speeds and having these suitably plotted one can readily study the performance of the machine for varying speeds and conditions of the external circuit. It will be seen that with an ordinary shunt wound dynamo, when the resistance of the external circuit is relatively high and falling, we are working (at any given speed) on a portion of the characteristic at which a rise of amperes is accompanied by a fall of voltage. This is the usual running condition of an ordinary shunt wound lighting generator, and the fineness of its field winding is so arranged to be suited to the high voltage represented on this portion of the characteristic. Contd - | ||