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 manufacturers' claims regarding the performance of electrical cut-out contacts and compensating windings.
| Identifier | ExFiles\Box 48\3\ Scan161 | |
| Date | 6th December 1920 | |
| Contd. -3- EFCL/T6.12.20. They claim as further advantages :- (1) That of the resulting reduction of the shunt current whilst the cut-out contacts are closed. (2) That owing to there being practically no reverse current and that the main contacts are protected by auxiliary carbon contacts, the main contacts are kept permanently in good condition and require no attention whatever. Whereas to some extent the makers' claims are true, nevertheless they are not true to the extent which they advertise. It would, for instance, be quite conceivably possible to mechanically so arrange the law of spring tension with change of gap, as to exactly balance magnetic traction corresponding to a given voltage and temperature (i.e. to given ampere turns) for every magnitude of gap. Thus, ignoring the slight effect due to remanence, there would, for any given temperature, be a critical voltage above which the cut-out would remain on, and below which the cut-out would remain off, in which case the compensating winding would be quite unnecessary and the series reverse amperes practically zero without the compensation. In any actual cut-out it is not likely that the spring control will increase in magnitude as the cut-out goes on, at the same rate as the magnetic traction corresponding to a given voltage at a given temperature, i.e. to a given number of ampere turns. It would, however, be possible to imagine that the motion of the lever, in operating some sort of variable carbon rheostat, progressively introduced resistance at such a rate as to reduce the ampere turns for every value of the gap, to such an extent as to exactly balance the spring control, in which case | ||