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 experiments on coil cases, identifying dielectric hysteresis loss as the cause of weakening effects.
| Identifier | ExFiles\Box 45\4\ Scan061 | |
| Date | 9th November 1922 | |
| Contd. -2- EFC1/T9.11.22. (1) Various standard Goshawk coils in standard bakelite (Elo) cases. (2) Other makes of coils. (3) Goshawk coils improved as regards secondary insulation but with varying numbers of turns. (4) Goshawk coils in stabilite cases. (5) 40/50 coils in stabilite and bakelite (Elo) cases. (6) Coils inside their cases, but suspended so as not to be in direct contact with the metal of the engine. (7) Coils outside their cases. (8) Insulating distance pieces between engine and coil. (9) Various coil cases and coils separate and together (bench experiments on insulation characteristics of Elo and mouldensite). but all these experiments have proved that the weakening effect on the coil lies in the electrical characteristics of the material of which the coil cases are made. This is not a case of electrical breakdown, so that measurements of breakdown voltage give no indication of this effect, neither does it appear to be mainly due to a straight forward D.C. leakage effect. It appears, however, to be more of the nature of energy loss due to a combination of a rather high inductivity of the material with a rather big dielectric hysteresis loss. Without going into detail, a number of experiments which have been conducted on the bench, using the coil cases as condenser dielectrics with tin foil plates, have borne out this notion. The effect on the chassis is also, as would be expected, very much accelerated if a tin foil is wrapped round the outside of the coil and earthed to the frame and it has been definitely proved that this is not merely a case of introducing a pure capacity on the high tension system, like a mica or glass dielectrics condenser. Contd. | ||