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).
Technical page discussing the properties and specifications of insulating oils for transformers and switches.
| Identifier | ExFiles\Box 24\2\ Scan109 | |
| Date | 25th January 1921 guessed | |
| - 22 - The fibrous insulating materials, including silk, that can be woven, are good dielectrics and have been mentioned on various occasions. It is not intended to treat these materials at the present moment nor will further mention be made of varnishes, eable compounds and various cohesive materials. The following few remarks concern the properties of oils. OILS. are used in transformers in order to safeguard the insulation of the windings and at the same time carry off by circulation the heat that is developed. Furthermore oils are used in switches in order to avoid the formation of sparkes in high tension circuits. A number of completely different materials are obtainable under the designation "oil" and it is therefore essential to test them according to the use to which the material is intended to be put. Transformer oils should be absolutely free from water and should contain no trace of acids as otherwise the cotton insulation and also the metallic conductors will be attacked. As transformers reach temperatures approaching 100° the volatility of the oils must be reduced to a minimum. The oils should not separate resinous and tarlike deposits under the action of the air, as these contaminate the windings and hinder circulation. The great dependence of the puncture voltage on the water content of the oil is shown by the following table given by Skinner - "Water Content of the Oil" "Puncture voltage of the oil 0.00% 9000 volts. 0.02 5000 " 0.04 4200 " 0.06 4000 " 0.08 3900 " 0.12 3800 " 0.20 3400 " The Association of Electricity Generating Stations has drawn up technical conditions concerning the supply of transformer and switch oils. According to this only highly refined mineral oils are to be used for transformers having a specific weights of not less than 0.85 and not over 0.92 at 15° and a flash point not below 160 to 180°. According to Engler the viscosity should be less than 8 at 20 and the freezing point should be below - 20°. At this temperature the oil must still remain liquid and clear in a test tube of 15 mm width and 4 c.m. height, after being cooled for an hour. The maximum loss by volatilization is fixed at 0.4% after 5 hours heating to 100°. It goes without saying that the oils must not be contaminated by sand fibres and the like. contd. | ||