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).
The electrical breakdown voltage tests of various insulating materials.
| Identifier | WestWitteringFiles\J\January1923\ Scan46 | |
| Date | 9th January 1923 | |
| Contd. -3- EPCR/T3 9.1.23. No. of Sample. | Material. | Thick-ness. | Voltage Reading. | Trans. Ratio. | Breakdown Voltage. | Volts per mil. ---|---|---|---|---|---|--- 1. | Oiled silk. | .002" | 125.0 | 25.0 | 3,150 | 1,575 2. | Diamond Fibre. | .013" | 151.5 | 25.0 | 3,790 | 291 3. | Bakelite. | .020 | 118.5 | 100.0 | 11,850 | 593 4. | " | .044 | 151.0 | 100.0 | 15,100 | 343 5. | Continental Bakelite. | .025 | 124.0 | 25.0 | 3,100 | 124 6. | " | .047 | 146.0 | 75.0 | 10,950 | 233 7. | Bakelite. | .149 | 179.0 | 100.0 | 17,900 | 121 With the exception of samples 1 and 5, the puncture of the material was accompanied by a distinct snap. With No.1 there was no noise, the breakdown being notified by lamps and voltmeter only. No.5 was not a clear breakdown, a small arc being struck through a small crack already existing in the material on a voltage of 3100 being reached. In nearly every case the puncture was found to be near the circumference of the area covered by the electrodes, which suggests that the surfaces of the electrodes, do not register properly, the contact pressure thus being unequal. Tests up to No.2 were carried out with the electrodes mounted on their original ebonite base, but on approaching 11,000 volts an arc was set up between the electrode supports. As the base was too short to allow of any adjustment the electrodes were remounted on a thick piece of fibre; the only thing available. This was used for the remainder of the tests. Specimens Nos 3 & 4 were ordinary bakelite discs. It will be seen that the thicker disc broke down at a much smaller voltage per mil. Contd. | ||