Transformer construction Resin insulated

Most power system transformers fall into two types of construction, dry-type or liquid immersed type. Dry-type include air insulated and solid insulated construction. Solid insulation is usually epoxy resin. 

The construction of transformers will be either liquid insulated in a steel tank or cast resin in a safety enclosure. Either type can be used for outdoor and indoor services, although additional weatherproofing will be needed for cast resin units. 

Encapsulation resins from Dow Chemical are solvent-free systems sold under the Voratron name. Flame-retarded halogen-free versions are available that meet UL94 V-0 requirements. These polyurethane crosslinked resins are both insulating materials and act as a construction material and housing for fixing electrical components in power distribution, transformers and cable joints. 

The distribution equipment comprises a number of metalclad, fireproof and weatherproof units with airbreak switches and circuit breakers. Although not a requirement in the standard, the transformers used in practice are generally of air-insulated or resin-encapsulated construction. The apparatus is robust to withstand rough handling, free-standing and... 

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