1.
Construction of

2.
3-Phase Transformer
• Introduction
• Types
• Construction of three phase power
transformer

3.
Introduction
• The generation of an electrical power at power station
is usually three phase and at higher voltages like 13.2
KV, 22 KV or some what higher.
• Similarly transmission of an electrical power is also at
very high voltages like 110 KV, 132 KV, 400 KV.
• T
o step up the generated voltages for
transmission purposes it is necessary to have three
phase transformers.
• Similarly to step down the transmission voltage to
distribution voltage, it is also necessary to have three
phase transformer.
.

4.
• Types on the basic of construction:
• Core type and Shell type
• Types on the basic of Uses
• Power transformer and Distribution transformer
• Types on the basic of Connection
Types of 3-Phase Transformer

5.
Construction of three phase power
transformer
Conservator Tank
Radiator/Cooling
fins
Cooling Fan
Metering
Instruments
Main Tank
Bushing
Carriage for transportation
Fig: Three phase transformer Complete view

6.
Tank
The tank protects the cores and the windings from the outside environment. It also acts as a container for
the oil. The tank is evacuated of air and other materials that may contaminate the oil and compromise the
insulations‘ dielectric properties.
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.
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.

7.
Tube for oil circulation
Fig: Three phase transformer with radiator removed

8.
Buchholz relay
Sensor (Temperature and Pressure)
Tube connecting main and
conservator tank

9.
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.
Cooler
As the oil absorbs heat from the system, it then transports this heat to the cooling system.
The cooling system collects hot oil, cools it through the air- or water-cooled tubes then
returns it to the windings and core.
Sensors:
Thermometers are used to monitor oil temperature. Pressure Relief Systems are safety
devices used to relieve overpressure in the event of oil flashing due to short circuits.

10.
HV and LV bushing
Laminated Core
Core Limb 1
(Out of 3 limb)

11.
Limb
surrounded
with
insulators
Outer HV winding
Insulator

12.
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. Low voltage winding is kept near to core as it requires reduced insulation
Insulating materials
Insulations act as a barrier system and are used to separate the windings from the
core and the two windings from each other. There are several types of insulations
that are used in transformers, which include oil, paper, tape, pressboard, and
laminated wood

13.
3 Phase transformer can be
• Made by connecting 3 separate
single phase transformer
• Three phase transformer in single
structure

14.
Advantages of single three phase unit
• Less space
• Weight Less
• Cost is Less
• Core will be smaller size
• More efficient
• Structure, switchgear and installation of single three
phase unit is simpler

15.
Advantages of three single phase unit
• Transported easily
• Only one spare 1 phase transformer is required for
standby instead of complete spare 3 phase
transformer
• Different KVA rating transformer can be used to
supply imbalanced load
• Can be operated in open delta (V-V) at reduced
capacity when one single phase transformer is
damaged

16.
Construction and Principle of Operation

17.
• The three cores are arranged at 120° from each other.
Only primary windings are shown on the cores for
simplicity.
• The primaries are connected to the three phase
supply.
• The three fluxes is also zero at any instant.

18.
• Hence the centre leg does not carry any flux.
• So if centre leg is removed, any two legs provide the
return path for the current and hence the flux in the
third leg.
• This is the general principal used in the design of
three phase core type transformers.

19.
Thank you!!