Class H insulation and its use in dry type station auxiliary & substation transformers

Industrial and utility engineers are becoming more demanding for fire and explosion resistant transformers for use in large generating stations, unit substations, and in network applications. Fire insurance companies are threatening and are raising rates for insurance protection on transformers installed in buildings or in industrial plants where human life is endangered. Oil-filled transformers are not approved by Underwriters for such indoor usage. Askarel-filled transformers, although approved, have been known to liberate toxic gases under certain conditions. And besides, some 500 gallons of such liquid, which is now almost impossible to procure, is required per 1000 KVA of transformer rating.