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).
Continued technical note discussing electrical leakage, the Johnsen-Rahbek effect, and ignition circuit components.
| Identifier | ExFiles\Box 45\4\ Scan093 | |
| Date | 18th November 1922 | |
| R.R. 199. (2_SOT) (SD670 19-7-17) MP:185865 5 (4) Contd. EFCl/T18.11.22. is hot, this effect is much increased and at the same time a certain amount of leakage may be felt. The increase in mechanical effect is probably due to a phenomenon known as the Johnsen and Rahbek effect, of which use has been made recently in a number of pieces of electrical apparatus, one of these being a sensitive potential indicator. The effect is that a flexible conductor such as a piece of tin foil is attracted to the surface of an insulator, on the other side of which is a conductor at a high potential, much more strongly than would be the case by direct electrostatic action, because although the conductivity of the points of contact of the foil to the insulator is not sufficient to allow the flow of any appreciable current, the conductivity of the material being rather greater, enables nearly the full potential to operate across a very thin film of air existing between them (foil and insulator). Because the leakage varies with temperature, this effect would reach a maximum at some temperature. (23) We do not yet know the actual value of the inductivity of bakelite or stabalite. We have searched but have no information on this point, and at the moment we have not suitable apparatus to find it, unless perhaps we could make up a condenser with this material as dielectric of sufficient capacity to give a reading on a our A.C. milliammeter. This we will attempt to do. (24) At this point we have received your latest note ref. Fl/M15.11.22. Energy leakage in the form of loss due to dielectric hysteresis would not be included in the combination of your (1) and (2). We must take steps to observe the insulation of the secondary circuit as you suggest. (25) As previously stated we propose building a core x7079c with greater section of iron core. (26) We do not think that a reasonable amount of pure capacity, such as obtained between primary and secondary wires, is any material detriment to the system, provided the secondary winding is adjusted to the optimum number of turns to charge the pure capacity involved to the optimum potential before breakdown. (27) It is also not our impression that self induction in the rest of the primary circuit, provided this is not associated with hysteresis loss, should be at all detrimental. Virtually it merely reduces the coefficient of magnetic coupling between the primary and secondary circuits, because, as it were, some of the turns are not coupled. We are prepared to agree that the ignition current were better, owing to hysteresis loss, not carried in conductors in iron Contd. | ||