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 DC leakage and insulation performance in a coil, particularly the effects of temperature on bakelite.
| Identifier | ExFiles\Box 45\4\ Scan065 | |
| Date | 9th November 1922 | |
| Contd. -6- PCL/T9.11.22. We have found by bench experiments that there is a slight D.C. leakage (insulation resistance of the order of half a megohm) between tin foils placed on the inside and outside of the coil case when the temperature becomes about 80°C. The leakage is first detectable when the coil case is brought to 60°C. (This test is done with 200 volts D.C. and a sensitive milliammeter). We have also shown that the case used as a condenser with the same foils behaves when cold almost precisely like a glass or mica dielectric condenser in brightening up the spark in the coil, but when the bakelite is hot, the behaviour seems to be radically changed to a degree which does not seem to be sufficiently accounted for by the presence of leakage effects. We are therefore of the opinion that the inductivity and with it dielectric loss under high frequency alternating potential is increased. This would be of the nature of a damping load on the primary oscillation between primary coil and primary condenser before the secondary voltage has reached a sufficiently high value to break down the spark gap. Taking all things into consideration it now appears that what is required to remedy the defect is some insulator with better electrical characteristics than the bakelite placed between the outside of the secondary windings of the coil and the inside of bakelite cases. This insulator would thus electrostatically be in series with the bakelite, but having presumably a much smaller inductivity, would allow | ||