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).
Dynamo modifications, analysing the effects of increased reluctance in the magnetic circuit and providing recommendations for 40/50 and 20/25 chassis.
| Identifier | ExFiles\Box 62\3\ scan0139 | |
| Date | 27th January 1931 | |
| -2- EFC4/AD27.1.31 contd. We judge from these results that the finer field winding is not an improvement, whereas the introduction of increased reluctance (air gap) in the magnetic circuit is an advantage provided it is not carried so far as materially to interfere with the cutting in. It will be understood that each of these curves is the best of a series for different main brush positions in the case of each modification, and that in each case the control brush is set to increase the output to the extent that the permissible temperature rise will allow. We wish further to say that it is now certainly proved that a concentric increase in the air gap is of the same value in its effective modification of the output curve as the polar modification, though it necessitates a readjustment of the main brush position in relation to the poles, which the other modification does not. The ordinary polar modification is therefore more applicable to existing machines, whereas the concentric modification is cheaper on a production basis. There is no reason to suppose that the relative appearance of the curves would be altered if they had all been taken on a 14.0 operating voltage basis. X.6076 It now having been proved that the introduction of a moderate amount of reluctance into the magnetic circuit is beneficial to this particular type of machines and that the form of air gap reluctance is of little consequence, we have been led to deduce that the additional reluctance should not be inserted at the air gap at all where it is of little value from other points of view, but should be introduced in the armature itself by increasing the slot size and reducing the permeance of the teeth in the manner already described, at which point it gives us the definite advantage of being able to reduce the ohmic resistance of the armature conductors and therefore to enable the machine to give a still greater output for a given degree of heating. This indicates the immediate line of improvement of dynamo performance and a result in this direction will shortly be available. Based upon this result we shall then be able to give our general recommendation of what is required in a dynamo to meet the demands which are now being made upon it in both cases of the 40/50 and the 20/25 chassis. EFC. | ||