This document discusses different cooling systems for transformers. It begins by introducing transformers and the need for cooling to prevent overheating. It then describes various cooling methods including air cooling, oil cooling, and nitrogen cooling. For oil cooling it explains natural, forced air, forced water, and combinations of forced methods. It concludes by discussing advantages of different cooling systems and their applications, and provides an overview of transformer protection devices.

2. COOLING SYSTEMS OF TRANSFORMERS
A Presentation on

3. Presented By:
•Malik Armughan Bhutta
SP14-BEE-012 B1B

4. TABLE OF CONTANTS
•Introduction
•Methods of Cooling
•Applications
•Protection

5. INTRODUCTION:
 Power transformers are key components for electricity supply systems.
 It convert energy at one voltage level to another voltage level. During the
process of energy transfer ,losses occur in the winding of the transformer.
This losses appear as heat that may burn the winding of the transformer.
 So to make the transformer healthier cooling is needed.

6. WHAT IS COOLING ?
When the Electric Machine is operating because or losses i.e
coper losses , eddy current losses coils of Machine heated up if
the rated temperature exceeds machine will burn out , to avoid
this have to cool it down and that process is called cooling

7. METHODS OF COOLING
There are two basic types of cooling for transformers :
•Air type cooling
•Oil immense cooling

8. Air Type cooling
• Air natural (AN) Cooling
• Air blast cooling
Oil immense cooling
• Oil natural (ON) cooling
• Oil natural air forced (ONAF)cooling
• Oil natural water forced (ONWF)
Cooling
• Oil forced air natural (OFAN) cooling
• Oil forced air forced (OFAF) Cooling
• Oil forced water forced (OFWF) Cooling

9. AIR NATURAL COOLING
• The transformers having smaller output(5-10KVA) are
cooled by this method.In this method the external surface
is sufficent to dissipate the heat produce by the losses.
• Such transformers are cooled by the combination of air
convection currents within the enclose case and by
natural radiation from the case itself.

10. AIR BLAST COOLING
• This type of cooling is used in dry type transformers.
• In this method ,heat dissipation is improved by a
continuous blast of air forced through the core and
windigs.
• The air blast is produced by means of external fans and
blowers.
• This type of cooling is limited to transformers of voltage
rating not exceeding 25kv.

11. DISADVANTAGES
•In this process the increase in insulation
strength is not obtained due to non-
immersion in oil.
•A regular maintenance is a must for this kind
of transformers.(i.e filter maintenance)

12. OIL NATURAL(ON) COOLING
• This is the most usual method of cooling.
• Here the assembly of core and windings is immersed in
insulating oil contained in iron tank.
• The heat produced in core and windings passed on to oil
by conduction. Oil in contact with heated parts rises and
its place is taken by cool oil from the bottom.
• The heated oil transfers its heat to the tank surface which
dissipates it to the surroundings

13. OIL NATURAL AIR FORCED COOLING
(ONAF)
• Here the assembly of core and windings is immersed in
insulating oil and cooling is improved by forced air over
the cooling surfaces
• The air is forced over external surfaces such as the
case,tubes and radiators, usually by means of fans
mounted external to the transformer.
• Medium to large capacity transformers are cooled by this
method.

14. ONAF PRACTICAL VIEW:

15. OIL NATURAL WATER FORCE COOLING
• In this type of cooling,the core and windings is immersed in an
insulating oil and cooling is improved by circulation of water
through copper cooling coils mounted above the transformer
core but below oil surface.
• The heated water is cooled in a spray pond or cooling tower.
• This method will be cheaper where a natural water head is already
available.

16. OIL FORCE AIR NATURAL COOLING
(OFAN)
•In this method, oil is circulated through the
transformer with the help of pump and cooled in a
heat exchanger by natural circulation of air.
•This method proves very useful where coolers have
to be well remove from the transformer.
•This method is not very common.

17. OIL FORCED AIR FORCED COOLING (OFAF)
• In this method,the oil is cooled in external heat exchanger using
air blast produced by fans.
• At light load, say upto 50% of rated load,(when the losses are
small) natural circulation of air may be sufficient to cool the
transformer.
• At higher loads,the pump and fans may be switch on by
temperature sensing elements.
• This arrangement results in higher efficiency of the system.

19. OFAF

20. OIL FORCED WATER FORCED COOLING
(OFWF)
• In this method,the heat oil pumped out from the main
tank to the radiator where the oil is cooled by the water
passing through copper tubes.
• The pressure of oil is kept higher than that of water
therefore,any leakage that occurs is from oil to water.
• There is no condensation problem.

21. NITROGEN COOLING
• Heat transfer analysis on a cryogenic cooling system is performed for HTS
transformers to be operated at 63–66 K.
• HTS windings are immersed in a liquid nitrogen bath where the liquid is
cooled simply by colder copper sheets vertically extended from the coldhead
of a cryocooler.
Liquid nitrogen in the gap between the windings and the copper sheets
develops a circulating flow by buoyancy force in subcooled state close to the
normal freezing point.
• Nitrogen functions as a heat transfer medium and an electrical insulating
fluid at the same time.

22. COUN’T
HTS windings in a main cryostat filled with subcooled liquid
nitrogen at around 65 K, and located an iron core through room-
temperature bore of the cryostat.
The subcooled liquid is continuously chilled by
two sets of cryocoolers in a secondary cryostat and
circulated through transfer lines to the main cryostat by a pump.

23. ADVANTAGES
•Faster Thermal Cycles
•Lower Temperature Limits
•Minimal Maintenance Costs
• Smaller Equipment
• Lower Electricity Usage

24. APPLICATIONS
• Air natural (AN) cooling is used for smaller output
transformer having rating 5-10kva.
• Air blast cooling is used for dry type transformer. The
voltage rating should not be exceed 25kv.
• The oil forced air forced (OFAF) cooling is usually used for
power transformer of rating 30mva and higher.

25. COUNT’D
•Oil forced water forced (OFWF) cooling is used for
transformers designed for hydro-electric power
plant.
•Cooling radiator system with natural cooling is
used for power transformers with a capacity of
10Mva

26. PROTECTION:
The power transformer protection is realized with
two different kinds of devices, namely the devices
that are measuring the electrical quantities affecting
the transformer through instrument transformers
and the devices that are indicating the status of the
physical quantities at the transformer itself

27. TYPES OF PROTECTION
The following discusses protection devices typically delivered as a part of the
power transformer delivery.
•Buchholz (Gas) Relay
•Pressure Relay
•Oil Level Monitor Device
•Winding Thermometer

28. THANKS
For the patience and listening to us