The document provides an overview of transformers, including their construction, main parts, protection devices, and maintenance. It discusses how transformers work by converting electrical power from one circuit to another through mutual induction of coils. Key components include the core, windings, tank filled with insulating oil, bushings, conservator tank, radiators, buchholz relay, cooling fan, PRD, indicators, and tap changer. The document also outlines transformer mechanical protections like the buchholz relay and electrical protections for faults. Routine maintenance is important to monitor the transformer's performance and condition.

1. Transformer Overview
Prepared By:
Muhammad Bilal
Electrical Technician

2. Contents:
a) Introduction
b) Construction
c) Parts of Transformer
d) Tap Changer
e) Transformer Mechanical Protection
f) Transformer Electrical Protection
g) Maintenance of Transformer

3. Introduction:
Transformer is a static device which convert electrical power from
one circuit to another without changing its frequency.
Power transformers are generally used in transmission network
for stepping up or down the voltage level.
It works on the principle of mutual induction of two coils or
Faraday Law’s Of Electromagnetic induction. When current in the
primary coil is changed the flux linked to the secondary coil also
changes. hence an EMF is induced in the secondary coil.

4. Construction of Transformer:
Basically a transformer consists of two inductive windings and
a laminated steel core. The coils are insulated from each other
as well as from the steel core. A transformer may also consist
of a container for winding and core assembly (called as tank),
suitable bushings to take out the terminals, oil is also used in
tank for cooling and insulation purpose.

5. Parts of Transformer:
These are the main components of a transformer.
1. Core
2. Windings
3. Transformer Tank
4. Transformer Oil
5. Bushings
6. Conservator Tank
7. Breather
8. Radiators
9. Buchholz Relay
10. Cooling Fan
11. PRD
12.Winding Temperature gauge
13.Oil Temperature gauge
14.Oil level indicator
15.Tap changer

6. Transformer core:
A core of the transformer is made up of ferromagnetic materials. The
main function of Core to support the winding and to provide flux
flowing path in the magnetic circuit. The soft iron core which made by
the thin metal strips lamination. They provide the low reluctance path
and high permeability for the flux.

7. Winding:
A winding is consists of several turns of the copper coil. winding are wrapped
around the limb and its separated by the primary side and secondary side.
Simply two types of the winding are used as…
On bases of supply two types as…
High voltage winding
Low voltage winding

8. Transformer Tank :
It is a main part of transformer. It is steel made box. Transformer core is placed
inside this tank. Windings and core are placed inside this tank. It is filled with
insulating oil ( mineral oil ). It have usually cylindrical or cubical shape
depending on transformer construction. It is coated internally and externally
with colour for safety point of view. Colour coating also provide protection in
case of winding connection with tank accidentally.

9. Transformer Oil:
Transformer oil (also known as insulating oil) is a special type of
oil which has excellent electrical insulating properties and is stable
at high temperatures. Transformer oil is used in oil-filled electrical
power transformers to insulate and to dissipate the heat of the
transformer (i.e. act as a coolant). It must therefore have
high dielectric strength, thermal conductivity, and chemical
stability.

10. Bushings:
The bushing is an insulating device that is made up of porcelain
materials. The terminal of the bushing is provided a path of the
conductor to the transformer tank.
Its rely on voltage rating may be a high voltage bushing or low
voltage bushing.

11. Bushings

12. Conservator Tank:
The conservator is mounted on a support structure above tank level and is equipped
with a filler plug, prismatic oil gauge, magnetic oil gauge and drain valve. Connection to
the top of the tank is made via pipe work, isolating valve and buchholz relay.
The conservator is designed to take up the expansion and contraction of the oil, due to
changes of temperature is service.
Conservator tank Buchholz relay

13. Radiators:
Radiator is a bank of hollow pipe line which is used to transfer the thermal
energy from one medium to another for the purpose of cooling. Some Bank are
used at the power transformer for cooling the transformer oil as well as reduces
the winding temperature under loading condition.
Radiators

14. Breather
The purpose of these silica gel breathers is to absorb
the moisture in the air sucked in by the transformer
during the breathing process.
Breather consist of silica gel which absorbs the
moisture from air.
The purpose of oil cup in breather is to absorb
dust particles in the air which is going to
transformer. Silica gel absorbs moisture and oil
cup absorbs the dust particle.
Silica gel
Breather Oil cup

15. Buchholz Relay
Buchholz relay is used for the protection of transformers from the faults
occurring inside the transformer. Short circuit faults such as inter turn faults,
winding faults, and core faults may occur due to the breakdown of the insulating
oil . Buchholz relay will sense such faults and closes the alarm circuit.
Buchholz relay
Buchholz relay

16. Cooling Fan
Cooling of Transformer is the process by which heat generated in the transformer
is dissipated or treated to the safe value. This is achieved by various cooling
methods of transformer available ,
We have cooling fan for this purpose ,
Fan start automatically when temperature reached
Up to set value and off when temperature become low
Transformer have two ratings as per cooling
As per ONAN=101.5MVA
As per ONAF=145MVA
Cooling fan

17. PRD(Pressure relief Device)
PRD (Pressure Relief Device) is a device which is used for avoiding high oil
pressure builds up inside the transformer during fault conditions. It is fitted on
the top of the main tank. The PRD allows rapid release of excessive pressure that
may be generated in the event of a serious fault. This device is fitted with an
alarm/trip switch.
Operating Pressure =10 PSI/0.689bar

18. PRD
PRD PRD

19. Oil level indicator
Oil level indicator is used to know the position or level of insulating oil in
the conservator tank of the transformer. This is a mechanical device
consists of three main parts
1) Float,
2) Bevel Gear arrangement and
3) Indicating dial.
The position of the float arm goes up or comes
down due to expansion and contraction of oil
due to increase and decrease in the temperature of oil
It is always recommended to maintain a minimum level of
oil in the conservator tank even when at lowest possible
temperature.

21. The WTI means winding temperature Indicator which indicates the winding
temperature of the transformer and operates the alarm, trip, and cooler control
contacts. This instrument operates on the principle of thermal imaging
Winding Temperature Indicator

22. Oil Temperature Indicator
A dial type thermometer mounted in a thermometer located on the transformer’s
Radiator tubes can be easily remove.
The top oil thermometer read the top oil temperature
The thermometer’s drag pointer indicates the maximum temperature reached.
Pointer change his position according to variation
in temperature of oil. Alarm and tripping contact
available ,when pointer reaches a pre-set value
contact make and give first alarm and then trip
signal to transformer.

23. Tap changer
The purpose of a tap changer is to regulate the output voltage of a transformer. It does
this by altering the number of turns in one winding and thereby changing the turns
ratio of the transformer.
Out put voltages controlled by changing in no of primary
turns by the help of tap changer.
There are two types of transformer tap changers:
1. On-load tap changer (OLTC)
2. D-energized tap changer (DETC)/ Off load tap changer

24. Transformer tap changer Animation

25. MR Tap changer

26. Transformer Mechanical Protections
Basically in terms of mechanical protection in power transformer there are
mainly four type of systems are used.
1. Buchholz Relay
2. Pressure Relay
3. Oil Level Monitor Device
4. Winding Thermometer

27. Following are Electrical Protection in transformer-
1. Earth fault
2. Over current
3. Over voltage/under voltage
4. 50BF( Breaker Failure)
5. 51NS
6. Differential Protection
7. Over fluxing
Transformer Electrical Protections

28. Transformer Maintenance

29. THE END
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