The properties of insulating materials used in instruments

The paper comprises a general discussion of the properties of insulating materials used in electrical instruments, with emphasis on the new synthetic organic materials. Values of dielectric constant and loss angle are tabulated. The structures of the main polymers of electrical interest and the relations between structure and electrical properties are briefly indicated. The advantages in instrument design of using small amounts of high-quality insulating materials, rather than larger amounts of the older conventional materials, are discussed with reference to the properties of the newer synthetic materials. The electrical behaviour of composite materials is discussed chiefly with reference to moisture absorption and electric strength. A Section deals with miscellaneous new materials for sealing against moisture, for cooling by an immersion medium, and for adhesive purposes. A short Bibliography is given, indicating the more important collections of information on insulating materials.