insulation porcelain[‚in·sə′lā·shən ¦pȯr·slən]
a dielectric used for high- and low-voltage power transmission lines and in the production of a variety of electrical equipment; a type of electrical ceramic.
The production technology of insulation porcelain makes it possible to manufacture articles of various shapes and sizes (dimensions from several mm to 1–2 m) by extrusion, soft plastic forming, and slip casting. Feldspathic insulation porcelain is the principal type produced; other varieties include alumina, zircon, and ascharite types. The material’s characteristics depend on its phase composition (the content of quartz, mullite, corundum, zircon, and vitreous phases). Bending strength ranges from 60 to 140 meganewtons per m2 (600–1,400 kg-force per cm2); electrical strength at 500 hertz, from 28 to 40 kilovolts per mm; volume resistivity at 20°C, from 1 × 1010 to 3.74 × 1012 ohm meters; and the dielectric constant at 50 Hz, from 6.3 to 8.2.
Because of the severe demands made on insulation porcelain, only pure ceramic raw materials of stable composition (kaolins, clays, quartz sand, zircon, and so on) are used in production.