Insulation systems for high voltage encapsulated transformers

Extensive development of encapsulated transformers for electrical distribution service has been going on since the late 1950´s. During this period oil-filled pad-mounted and vault-type transformers have made rapid inroads toward replacing the older more conventional pole or overhead types. However, solid insulation or cast-type transformers are still not broadly marketed or have received customers´ acceptance on the American electrical utilities scene. There is good reason for this. Many problems have been encountered, some of which progressive technology has solved and some of which even today offer a challenge to and tax the imagination and the economic resources of the industry.