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).
Translation of a German article on insulating materials for electrical purposes, originally published in 1917.
| Identifier | ExFiles\Box 24\2\ Scan088 | |
| Date | 25th January 1921 | |
| EFP x 1104 (filed 25-1-21) COPY. does this interest you By2012-20 TRANSLATION FROM AN ARTICLE IN ELECTROTECHNIK. UND MASCHINENBAU IN THE ISSUES OF 2nd DECEMBER AND 9th DECEMBER 1917. Insulating Materials for Electrical Purposes. by Dr. Bultemann. --------------------- In electrical engineering two kinds of materials of construction should be distinguished, firstly, the conductors, and secondly, the non-conductors of electricity. In the former we assume that the electrons are present in infinite numbers and that they move freely between the molecules. On the other hand the insulating materials are regarded as being composed of molecules, each of which contains an atom, or aggregate of atoms bound to a positive electron and another atom bound to a negative electron. Each molecule thus contains two charges of an opposite kind. The use of insulating materials is very extensive and varied and cannot be discussed here exhaustively. This applies both to the experimental investigations up to date, concerning the effects of electric forces and also to the behaviour and properties of the different insulating materials themselves. In order to form an opinion of the electric qualities of a solid dielectric, it is necessary to determine its insulating resistance and the puncture voltage. No insulating material is an absolute non-conductor, and, on this account, the conductivity or the reciprocal value of the resistance has to be determined. The measurement gives the current stream through the material itself and over its surface. The dampness of the air must be allowed for in measuring the surface insulation, one part of the current flows through the uppermost layer and the other part through the body of the material; therefore, in the measurement the sum of both these processes is obtained. The Regulations of the Institution give methods of testing for this case. The test voltage is generally 1000-volt direct-current, and with particularly good insulation materials, double this value is taken as the resistance measured are smaller when measured with higher voltages. Displacement currents must be excluded, and the moving-coil galvanometer may be regulated by means of a shunt. In order to determine the puncture voltage it is best to use a transformer as source of current, arranged so as to permit the gradual rise of the test voltage, and capable of giving an output of several kilowatts, as otherwise small faults are not broken down completely, and remain hidden. | ||