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 operation of a Type A Dynamo, focusing on brush arrangement, resistance circuits, and modifications.
| Identifier | WestWitteringFiles\C\August1919\ Scan42 | |
| Date | 13th August 1919 | |
| Contd. -3- EFC1/T13.8.19. round in the direction of rotation and reduces the E.M.F's acting in the local resistance circuits, so that the currents in these resistances are gradually reduced to zero and there comes a time when the auxiliary brushes are inoperative. The machine is then operating as a simple shunt dynamo without brush lead. On further increase of speed, and therefore of current delivered to the battery, the current in these resistances reverses, which means that the auxiliary brushes begin to supply a portion of the main current./ At the same time the effect on the main field is now demagnetising. This effect goes on increasing. A time arrives when the auxiliary brushes are supplying half of the main and field currents and at this instant the sections of the armature between A + and M + and between M - and A - are not traversed by current, so that the C²R losses in the armature are confined to half of the armature only. The magnitude of the resistances was so arranged that this condition obtained at the average speed of the dynam. In the present Type A Dynamo, the arrangement is some- what modified. The resistances are dispensed with and the brushes A + and M + also M - and A - are respectively connected together without appreciable resistance. If the brushes remained in the same positions, however, an undue amount of control would be introduced, causing the current-speed curve to droop too much at high speed. The E.M.F's in the local circuits corresponding to these two connected pairs of brushes must therefore be reduced, - and this is effected by turning the whole system of brushes back against the rotation through an angle of about 20° until the Contd. | ||