Transformer insulations system

Transformer insulation systems can generally be categorized as liquid-solid, solid-gas or solid-solid. Dependent on the type of insulation, amount and how it is used in conjunction with the other parts of the transformer, are transformer voltage insulation classes, basic impulse insulation levels, average winding temperature rise at rated KVA, and operating environment. A number of characteristics and performance requirements necessary for proper electrical, mechanical and thermal performance are reviewed. Insulation materials are identified and described briefly relating to use in transformer application. This paper also includes recent improvements in the liquid-solid insulation system by using additives to improve mineral oil life and insulation thermal performance. A transformer having the proper insulation system will generally dictate its selection and application for indoor and outdoor service, voltage, fire or explosion hazard elimination, and environmental conditions such as clean and dry or highly corrosive or wet and dusty locations.