Inorganic insulations for high voltage dry type transformers

High voltage dry type transformers contain geometrically complex combinations of various insulating materials. For thermal resistance, non-flammability and resistance to corona, inorganic insulations may be desirable where cost effective. Mica, chrysotile asbestos and an inorganic fiber, anthophyllite, are compared in terms of molecular structure and their applicability as high voltage insulations. An insulating paper containing anthophyllite fiber, designated HVP, is evaluated in terms of electrical properties, corona start voltage and voltage endurance.