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).
Test results on the conductance and dielectric strength of various papers after heating cycles.
| Identifier | ExFiles\Box 165\5\ img013 | |
| Date | 31th May 1928 guessed | |
| -2- Contd. (2) The above tests were repeated, but this time readings were also taken as the temperature fell. An abridged table of results is given below, shewing the initial conductance for each material with the corresponding temperature, and the conductance on returning to that temperature after each cycle of temperature, 100°C. being the peak temperature each time. A final check reading was taken on each paper after allowing it to stand for two days. | Paper. | 1st. Cycle. | 2nd. Cycle. | After standing two days. | |--------------------|---------------------------------|----------------------------------------------|--------------------------| | American varnished | 40°C .001 micromhos. 100°C .201 | 40°C .001 micromhos. 100°C .064, 40°C .0003 | 40°C 0 micromhos. | | Symons waxed. | 70°C .002 micromhos. 100°C .017 | 70°C .001 micromhos. 100°C .005, 70°C .0003 | 70°C 0 micromhos. | The Symons varnished paper still shewed no signs of leaking. These results shew that the material is improved, in respect of leakage, by repeated heatings, and moreover that this improvement is permanent. The American paper was then taken up to 150°C. at which temperature it was maintained for two hours. There were no signs of it weakening; on the contrary it appeared to improve, as the conductance gradually became less until at the end of two hours at 150° the conductance was almost zero. (3) Some new samples of each paper were subjected to a breakdown voltage test, from which was obtained the dielectric strength in terms of peak volts per .001" thickness. These are given in the table below. (4) The samples of paper which had been subjected to the heating tests, were tested for dielectric strength in a similar manner, and thus the effect of heating on the dielectric strength ascertained. These are also given below with the results from (3). | Paper. | New. | After being heated. | |--------------------|------|---------------------| | American varnished | 999 | 1237 | | Symons varnished. | 1788 | 1214 | | Symons waxed. | 1482 | 1213 | Contd. | ||