Two types of oil-filled transformers are commonly used:
● With expansion tank (conservator)
● Sealed
In this type of transformers windings and core are immersed in oil, in a tank with radiators; oil plays both functions of insulating material and cooling fluid.
Common applications of oil-filled transformers with conservator are:
● As step-up transformers in power plants.
● As step-down transformers in EHV/EHV, EHV/HV and HV/MV utilities substations (primary voltages above 52 kV).
● As step-down transformers in HV/MV or MV/MV industrial plants substations, with rated power above 2.5 MVA.
Oil-filled sealed transformers (without conservator) are mainly used in distribution networks (MV/LV) and in installations up to 52 kV, with a rated power up to 2.5 MVA, although some manufactures built this type of transformers up to 30 MVA.
The degree of protection (IP) provided by the tank allows that both types of transformers can be installed outdoors.
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