Transformers are used to transfer
electrical energy from one circuit to another through electromagnetic
induction. They are used either to step up or step down voltage levels. A
transformer is made of several different parts that function in their own different
ways to enhance the overall functioning of a transformer. These include core,
windings, insulating materials, transformer oil, tap changer, conservator,
breather, cooling tubes, Buchholz Relay and explosion vent. The core, windings,
insulating materials and transformer oil are seen in almost every transformer,
while the other components are seen in transformers that are more than 50 KVA.
Core
The core of the transformer is used to
support the windings. It is made of soft iron to reduce eddy current loss and
Hysteresis loss, and provides low reluctance path to the flow of magnetic flux.
The diameter of a transformer’s core is directly proportional to copper loss
and inversely proportional to iron loss.
Windings
Windings consist of several copper coil
turns bundled together, each bundle connected to form a complete winding.
Windings can be based either on the input-output supply or on the voltage
range. Windings that are based on supply are classified into primary and
secondary windings, meaning the windings to which the input and output voltage
is applied respectively. On the other hand, windings based on voltage range can
be classified into high voltage and low voltage windings.
Insulating
materials
Insulating materials like papers and
card boards are used to isolate primary and secondary windings from each other
as well as the transformer core. These windings are made of copper due to high
conductivity and ductility. High conductivity minimizes the amount of copper
needed and minimizes losses. Moreover, high ductility results in easy bending
of conductors into tight winding around the core that also minimizes the amount
of copper and volume of winding.
Transformer
oil
The transformer oil insulates as well
as cools the core and coil assembly. The core and windings of the transformer
must be completely immersed in the oil that normally contains hydrocarbon
mineral oils.
Conservator
The conservator is an airtight metallic
cylindrical drum fitted above the transformer that conserves the transformer
oil. It is vented at the top and is filled only half with the oil to allow
expansion and contraction during temperature variations. However the main tank
of the transformer with which the conservator is connected is completely filled
with the oil through a pipeline.
Breather
The breather is a cylindrical container
filled with silica gel, which is used to keep the air that enters the tank
moisture-free. This is because the insulating oil when reacts with moisture can
affect the insulation and cause internal faults, which is why it is a must to
keep the air free from moisture. In the breather, when the air passes through
the silica gel, the moisture contents are absorbed by the silica crystals.
Tap
changer
To balance voltage variations within
the transformer, tap changers are used. There are two types of tap changers –
on load and off load. In on load tap changers, tapping can be changed without
isolating transformer from the supply, while in off load, the transformer needs
to be disconnected from the supply.
Cooling
tubes
As the name suggests, cooling tubes are
used to cool the transformer oil. The circulation of oil within the transformer
may be natural or forced. In the case of natural circulation, when the oil
temperature rises, the hot oil naturally moves to the top and cold oil moves
down, while in case of forced circulation, an eternal pump is used.
Buchholz
Relay
Placed over the connecting pipe that
runs from the main tank to conservator tank the Buchholz Relay senses the
faults occurring within the transformer. It operates by the gases emitted due
to decomposition of transformer oil during internal faults. Thus, this device
is used to sense and in turn protect the transformer from internal faults.
Explosion
vent
The boiling hot oil from the
transformer is expelled during internal faults through the explosion vent to
avoid explosion of the transformer. This is generally placed above the level of
the conservatory tank.
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