Electrical enggg. ppt

1. STANI MEMORIAL COLLEGE OF ENGG. &
TECHNOLOGY,PHAGI JAIPUR -303005
A Ppt Presentation on
TRANSFORMER
Submitted by
RAKESH RAUSHAN
12ESTEE021
Submitted to
Abhishek kr. Sharma
H.O.D Electrical Department

2. What is Transformer ??
• A transformer is a
electromagnetic static
device which is use to
convert high alternating
voltage to a low
alternating voltage and
vice versa, keeping the
frequency same.

3. The main principle of operation of a transformer is mutual
inductance between two circuits which is linked by a common
magnetic flux. A basic transformer consists of two coils that are
electrically separate and inductive, but are magnetically linked
through a path of reluctance.
WORKING OF TRANSFORMER
WORKING PRINCIPLE

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.
•core is constructed by assembling
laminated sheets of steel, with minimum
air-gap between them (to achieve
continuous magnetic path).
•The silicon steel used is to provide high
permeability and low hysteresis loss.
•Laminated sheets of steel are used to
reduce eddy current loss.

5. Classification of transformer
• As per phase
1. Single phase
2. Three phase
• As per core
1. Core type
2. Shell type
• As per cooling system
1. Self-cooled
2. Air cooled
3. Oil cooled
• As per service
1.Power transformer
2.Distribution transformer

6. Three phase Transformer

7. Transformer classified as
per core

8. COOLING METHODS OF A TRANSFORMER
For dry type transformers
•Air Natural Or Self Air Cooled
Transformer
• Air Blast
For oil immersed tranformers
•Oil Natural Air Natural (ONAN)
•Oil Natural Air Forced (ONAF)
•Oil Forced Air Forced (OFAF)
•Oil Forced Water Forced (OFWF)

9. Air Natural Or Self Air Cooled Transformer
This method of transformer cooling is generally used in small transformers (upto 3
MVA). In this method the transformer is allowed to cool by natural air flow
surrounding it.
Air Blast
For transformers rated more than 3 MVA, cooling by natural air method is
inadequate. In this method, air is forced on the core and windings with the help of
fans or blowers. The air supply must be filtered to prevent the accumulation of dust
particles in ventilation ducts. This method can be used for transformers upto 15
MVA.

10. This transformer cooling method is
generally used for large transformers
upto about 60 MVA.
This method can be used for
transformers upto about 30 MVA.
ONAF
ONAN

11. Oil Forced Air Forced (OFAF)
This type of cooling is provided for higher rating transformers at substations or
power stations.

12. Oil Forced Water Forced (OFWF)
This method is similar to OFAF method, but here forced water flow is
used to dissipate hear from the heat exchangers.

13. Power Transformer
Power transformers are used in
transmission network of higher
voltages for step-up and step down
application (400 kV, 200 kV, 110 kV,
66 kV, 33kV) and are generally rated
above 200MVA.
Power transformer generally operated
at full load. Hence it is designed such
that copper losses are minimal.

14. Distribution Transformer
• It is used for end user
connectivity. (11kV, 6.6 kV, 3.3
kV, 440V, 230V) and are
generally rated less than 200
MVA.
• Distribution transformer is
always online and operated at
loads less than full load for
most of time. Hence, it is
designed such that core losses
are minimal.

15. A wide variety of transformer designs are used for
different applications.
 Auto-transformer
 Poly-phase transormer
 Leakage transformer
 Resonant transformer
 Instrument transformers

16. AUTO-TRANSFORMERS
Autotransformer is a
one winding
transformer in which
a part of the winding
is common to both
HV & LV sides.

17. POLY-PHASE TRANSFORMER
• Three separate single phase
transformers are suitably
connected for 3 phase
operation.
• A single three phase
transformer in which the
cores and windings for all
the three phases are
combined in a single
structure.

18. INSTRUMENT TRANSFORMERS
A current transformer is
a measurement device
designed to provide a
current in its
secondary coil
proportional to the
current flowing in its
primary.
A voltage
transformer are
designed to have an
accurately known
transformation ratio
in both magnitude
and phase, over a
range of measuring
circuit impedances..

19. Losses in transformer
(I) Core Losses Or Iron Losses
a) Hysteresis loss
b) Eddy current loss
(ii) Copper loss
Copper loss is due to ohmic resistance of the transformer
windings. Copper loss for the primary winding is I1
2R1 and for secondary
winding is I2
2R2. Where, I1 and I2 are current in primary and secondary
winding respectively, R1 and R2 are the resistances of primary and
secondary winding respectively.

20. Hysteresis Loss
The magnetic core of transformer is made of ′Cold Rolled Grain Oriented Silicon Steel′. Steel
is very good ferromagnetic material. That Ferromagnetic substances have numbers of
domains in their structure. The domains are situated randomly in the structure of
substance. Whenever external magnetic field is applied , these randomly directed domains
get arranged themselves in parallel to the axis of applied mmf. After removing this external
mmf, maximum numbers of domains again come to random positions, but some of them
still remain in their changed position. Because of these unchanged domains, the substance
becomes slightly magnetized . To neutralize this magnetism, there will be a consumption of
electrical energy which is known as Hysteresis loss of transformer.

21. Eddy current loss
In transformer, we supply alternating current in the primary, this alternating current
produces alternating magnetizing flux in the core and as this flux links with secondary
winding, there will be induced voltage in secondary, resulting current to flow through the
load connected with it. Some of the alternating fluxes of transformer; may also link with
other conducting parts like steel core or iron body of transformer etc. As alternating flux
links with these parts of transformer, there would be a locally induced emf. Due to these
emfs, there would be currents which will circulate locally at that parts of the transformer.
These circulating current will not contribute in output of the transformer and dissipated as
heat. This type of energy loss is called eddy current loss of transformer.

22. Transformer Protection
1.Buchholz Relay
2.Earth Fault Relay
3.Differential Relay
4.Overcurrent Relay
General Faults in Transformer
1.Open circuit fault
2.Overheating or Overloading fault
3.Winding short circuiting fault
4.Faults due to lightning
Protecting Relay

23. Buchholz Relay Protection
Buchholz relay for transformer
protection is only applicable for oil
immersed transformer- used mostly
for transformers with ratings above
750KVA, it provides protection from
all kinds of faults.
The concept of this relay is to utilize
Hydrogen producing from fault heat.
That is if a fault occurs either slow
or fast there will be immense heat
and this heat will create hydrogen
from transformer oil.

24. Earth Fault Relay
“Earth fault” means one of the core is being connected or leaked to the earthing or
grounding. This happens when insulation is damaged and coil is in touch with transformer
body and body of transformer is certainly connected to the ground for safety.

25. Differential protection
Differential protection is provided in the electrical power transformer rated more
than 5MVA.

26. Bushing
Bushing is an important part of power
transformer. It is used to insulate the
incoming or outgoing conductor into or
out of a grounded barrier, in power
transformer case is the transformer
main tank. The bushings connect the
windings of the transformer to the
supply line and insulate the feed
through conductor from the
transformer main tank.