Properties and characteristics of insulating materials

The subject of insulating materials has been considered in this paper under five main headings, of which four are dealt with in this abstract. The fifth section was chiefly concerned with the properties of well-known forms of moulded insulation, which were considered in more detail in an earlier paper by the present author. Section 1 here deals with the manufacture and properties of porcelain, and describes the various processes in common use, and their application to transmission and terminal insulators. Section 2 deals with mica insulation, the physical properties of mica, its use in its natural form as an insulator, and the various fabricated insulators in which it plays an important part. Section 3 treats of fibrous insulation, including papers and cloths and various insulators made with these materials as a base, such as ¿Micarta¿, etc. Section 4 deals with liquid insulation, including transformer and switch oils and varnishes employed in impregnation and dipping processes in connection with coils, etc., used in electrical apparatus.