Several
types of transformer tank construction are used to prevent exposingliquid to
the atmosphere.
These types
are as follows:
Free
breathing: This type is open to the atmosphere (i.e., the airspace above the
liquid is at atmospheric pressure). The transformer breathes as the air
pressure and temperature change outside the tank. Some of these transformers can be equipped
with dehydrating compounds in the breather.
Conservator
or expansion-tank: These transformers are equipped with small expansion tanks
above the transformer tank. The transformer tank is completely filled with oil,
and the transformer breathes by means of this small tank, usually through a
dehydrating compound.
The purpose
of the small tank is to seal the transformer fl uid from the atmosphere and to
reduce oxidization and formation of sludge.
Sealed tank:
These transformers are equipped with an inert gas, such as nitrogen that is
under pressure above the liquid in the transformer tank. Generally, the
pressure range for this type of transformer is −8 to +8 lb/in.2
Gas-oil
sealed: These transformers have an auxiliary tank to completely seal the
interior tank, containing transformer liquid, from the atmosphere.
Vaporization:
This type of transformer uses a special nonflammable insulating fluid, such as
florocarbon (General Electric R-113), which is nonflammable, and a special
condenser assembly welded on top of the transformer tank.
The cooling
tube ends are swaged and welded to tube headers. This transformer uses the
technique of sprayed liquid on core and coil assembly (i.e., vaporization cooling
known as pool boiling).
The purpose
of the condenser is to cool the boiling vapor into liquid for continued
circulation of the fluid.
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