What is the difference between Sealed Resin Epoxy Encapsulated Transformers and Ventilated Transformers that otherwise have similar parameters (kVA, voltage)?

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Issue:
Transformer types intended for different purposes must be chosen carefully, even if the basic electrical requirements for which they are needed are satisfied.

Product Line:
LV Transformers

Environment:
Applies to SquareD/Schneider Electric Sealed Resin Epoxy Encapsulated Transformers and Ventilated Transformers

Cause:
Different Transformer types having similar electrical characteristics can have dissimilar physical features

Resolution:

An encapsulated transformer has the core and coil surrounded by an epoxy resin and sand encapsulation material, which is baked, effectively becoming a ``brick`` that is locked into the enclosure, effectively sealing out moisture and contaminants from the core and coil. Heat removal from the transformer is only provided through the surface of the enclosure. The encapsulated transformer utilizes a Class 180 insulation system with a standard temperature rise of 115degC. This is the principal method used in manufacturing small transformers (below 15kVA.) It is not as popular at higher KVA ratings because of the higher cost, greater weight, and lower impedance than comparable Ventilated Transformers. Square D/Schneider Electric can provide Sealed Resin Epoxy Encapsulated Transformers 0.05 KVA through 25 KVA single phase, and 3 KVA through 30 KVA three phase. As well, Sealed Resin Epoxy Encapsulated Transformers are offered as wall mounted, with no wall clearance required beyond that provided by the mounting provisions. They do require 12 inches of clearance around the sides and top to allow for sufficient air circulation to remove the heat from the surface of the transformer (this requirement is clearly marked on the nameplate of the transformer in accordance with UL requirements).

Ventilated Transformers have the core and coil enclosed by a steel enclosure except for ventilation openings. Air circulates around the core and coil and is removed primarily through the ventilation openings. Newer, Energy Efficient (EE Type) Transformers require 3 inches of clearance around the ventilation openings (this requirement is clearly marked on the nameplate of the transformer in accordance with UL requirements.) Older, Non- Energy Efficient Transformers require 6 inches of clearance around the ventilation openings.
The Ventilated Transformers typically utilize a Class 220 insulation system with a standard temperature rise of 150degC. This is the principal method used in manufacturing transformers 15kVA and larger. It is more popular than Sealed Resin Epoxy Encapsulated Transformers at these higher KVA ratings because of the lower cost, lower weight, and better impedance than comparable Sealed Resin Epoxy Encapsulated Transformers. Square D/Schneider Electric can provide Ventilated Transformers 15kVA through 500kVA single phase (UL up to 167kVA,) and 15kVA through 2500kVA three phase (UL through 1000kVA.)