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).
Page discussing the effects of hysteresis and eddy currents on an armature and pole pieces in a magnetic system.
| Identifier | ExFiles\Box 4\5\ 05-page071 | |
| Date | 11th August 1929 guessed | |
| -2- Contd. Secondly, suppose the material of the armature and pole pieces to suffer from hysteresis but no eddy currents. The core flux will still be a maximum when the armature is horizontal, as maximum flux will still occur coincidentally in time with the maximum magnetising force. But the core flux will not be zero when the armature is vertical, and the magnetising force zero, on account of remanence which must necessarily coexist with hysteresis. Instead, the core flux will fall to a zero value rather later in the revolution (Fig.3). This will mean that there is on the whole a resultant magnetic drag on the armature, the torque corresponding to which is proportional to the hysteresis of the material. Whereas in the previous case, the backward and forward pulls on the armature were of equal duration, now the backward pulls are of longer duration. The work done in overcoming the resultant backward torque appears as heat in the armature and pole pieces, and increases proportionally with the speed. Thirdly, suppose the armature and pole pieces to be subject to eddy currents. Eddy currents being merely little electric currents in conducting paths in the magnetic material, their effect may be simulated by supposing the armature and pole pieces to be eddy-current-less in themselves but each to be wound with a short circuited winding of some definite conductance. It will be useful to consider an extreme case in which these conducting paths conduct almost perfectly, i.e. have nearly zero resistance. There can then be no appreciable | ||