Transformers

SUBMITTED BY:-
NAME- SOUMYA RANJAN DAS
DISPLINE-EEE
ROLL NO.-1601209194
COLLEGE- SILICON INSTITUTE OFTECHNOLOGY
TRAINING PERIOD- 28/05/2018 – 27/05/2018
TRANSFORMER

INTRODUCTION
 A transformer is a static device.
 The word ‘transformer’ comes form the word
‘transform’.
 Transformer is not an energy conversion device, but it is
device that changes AC electrical power at one voltage
level into another through the action of magnetic field
but with a proportional increase or decrease in the
current ratings., without a change in frequency.
 It can be either to step-up or step down.
 It works on the principle of mutual induction

WORKING
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.
The working principle of the transformer can be
understood from the figure below

WORKING….
If the second coil circuit is closed, a current flows in it and
thus electrical energy is transferred magnetically from the
first to the second coil. The alternating current supply is
given to the first coil and hence it can be called as the
primary winding. The energy is drawn out from the second
coil and thus can be called as the secondary winding.
In short, a transformer carries the operations shown below:
 Transfer of electric power from one circuit to another.
 Transfer of electric power without any change in frequency
 Transfer with the principle of electromagnetic induction.
 The two electrical circuits are linked by mutual induction

TRANSFORMER CONSTRUCTION:
 For the simple construction of a transformer, you must
need two coils having mutual inductance and a
laminated steel core.
 The two coils are insulated from each other and from the
steel core.
 The device will also need some suitable container for the
assembled core and windings, a medium with which the
core and its windings from its container can be insulated.

TRANSFORMER CONSTRUCTION....
 In order to insulate and to bring out the terminals of the
winding from the tank, apt bushings that are made from
either porcelain or capacitor type must be used.
 In all transformers that are used commercially, the core is
made out of transformer sheet steel laminations
assembled to provide a continuous magnetic path with
minimum of air-gap included.
 The steel should have high permeability and low
hysteresis loss.

BASIC PARTS OFATRANSFORMER
1. Laminated core 6. Oil Conservator
2. Windings 7. Breather
3. Insulating materials 8. Cooling tubes
4. Transformer oil 9. Buchholz Relay
5. Tap changer 10. Explosion vent
Of the above, laminated soft iron core, windings and
insulating material are the primary parts and are present in
all transformers, whereas the rest can be seen only in
transformers having a capacity of more than 100KVA.

CORE:-
 The core acts as support to the winding in the transformer.
 It provides a low reluctance path to the flow of magnetic flux.
 It is made of laminated soft iron core in order to reduce eddy
current loss and Hysteresis loss.
 The composition of a transformer core depends on such as
factors voltage, current, and frequency.
 The diam. of the transformer core is directly proportional to
copper loss and is inversely proportional to iron loss.
 If the diam. of the core is decreased, the weight of the steel in
the core is reduced, which leads to less core loss of the
transformer and the copper loss increase.When the diameter
of the core is increased, the vise versa occurs.

WINDING:-
 Winding consists of several turns of copper conductors
bundled together, and are connected in series.
 Two sets of winding are made over the transformer core and
are insulated from each other.
Winding can be classified in two different ways:
1. Based on the i/p and o/p supply
2. Based on the voltage range
Based on I/O supply, winding can be classified as:
1. Primary winding –
These are the winding to which the input voltage is applied.
2. Secondary winding –
These are the winding to which the output voltage is applied.

WINDING:-
Based on voltage range, winding are classified as:
1. High voltage winding –
 It is made of copper conductor.
 The no. of turns made shall be the multiple of the no. of
turns in the low voltage winding.
 The conductor used will be thinner than that of the LV
winding.
2. Low voltage winding –
 It consists of fewer number of turns than the HV winding.
 It is made of thick copper conductors. This is because the
current in the LV winding is higher than that of HV winding.
Input supply to the transformers can be applied from either
LV or HV winding based on the requirement.

INSULATING MATERIALS:-
EXPLOSIONVENT:-
 It is used to expel boiling oil in the transformer during heavy
internal faults in order to avoid the explosion of the transformer.
 During heavy faults, the oil rushes out of the vent.
 The level of the explosion vent is normally maintained above the
level of the conservatory tank.
 Insulating paper and cardboard are used in transformers to
isolate P and S winding from each other and from the
transformer core.
 Transformer oil is another insulating material. It can also cool
the core and coil assembly.
 The core and winding must be completely immersed in the oil.
 Normally, HC mineral oils are used as transformer oil.

CONSERVATOR:-
 The conservator conserves the transformer oil.
 It is an airtight, metallic, cylindrical drum that is fitted
above the transformer.
 It is vented to the atmosphere at the top, and the normal
oil level is approximately in the middle of the conservator
to allow the oil to expand and contract as the
temperature varies.
 It is connected to the main tank inside the transformer,
which is completely filled with transformer oil through a
pipeline.

BREATHER:-
 It controls the moisture level in the transformer.
 If the insulating oil encounters moisture, it can affect the
paper insulation or may even lead to internal faults.
 Hence, it is necessary that the air entering the tank is
moisture-free.
 It is a cylindrical container that is filled with silica gel.
 When the atmospheric air passes through the silica gel of
the breather, the air's moisture is absorbed by the silica
crystals.
 It acts like an air filter for the transformer and controls the
moisture level inside a transformer.
 It is connected to the end of breather pipe.

TAP CHANGER:-
 The o/p voltage of transformers vary according to its i/p
voltage and the load. During loaded conditions, the
voltage on the o/p terminal decreases, whereas during
off-load conditions the o/p voltage increases.
 To balance the voltage variations, tap changers are used.
 It can be either on-load tap changers(ONTC) or off-load
tap changers(OFTC).
 In an OLTC, the tapping can be changed without isolating
the transformer from the supply.
 In an OFTC, it is done after disconnecting the transformer.

COOLING TUBES:-
 These are used to cool the transformer oil.The transformer
oil is circulated through it.
 The circulation of the oil may either be natural or forced.
BUCHHOLZ RELAY:-
 It is a protective device container housed over the connecting
pipe from the main tank to the conservator tank.
 It is used to sense the faults occurring inside the transformer.
 It is a simple relay, operated by the gases emitted during the
decomposition of transformer oil during internal faults.
 It helps in sensing and protecting the transformer from
internal faults.

WHYTRANSFORMERSARE RATED IN
KVA?
The iron losses depend on the supply voltage while the copper
depend on the current .The losses are not dependent on the
phase angle between current and voltage. Hence the rating of
the transformer is expressed as a product of voltage and
current calledVA rating of transformer. It is not expressed in
watts or kilowatts. Most of the time, rating is expressed in kVA.

CLASSIFICATION OFTRANSFORMER:
 As per supply
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 purpose
1. Step-up transformer
2. Step-down transformer
 As per the use
1. Power transformer
2. Distribution transformer
3. Instrument transformer
i. Current transformer
ii. Potential transformer

TRANSFORMER CLASSIFIEDAS PER SUPPLY:
1. SINGLE-PHASETRANSFORMER
A single phase transformer has two or more windings
coupled by a common magnetic core

2.THREE-PHASETRANSFORMER
 Normally , when three-phase is required, a single enclosure
with three primary and three secondary windings wound on
a common core is all that is required.
 However three single-phase transformers with the same
rating can be connected to form a three-phase bank.
 Since each 1ф transformer has a primary and secondary
winding, then 3 1ф transformers will have the required 3 P
and 3 S windings and can be connected in the field either Δ-Δ
or Δ-Y to achieve the required three-phased transformer bank

TRANSFORMER CLASSIFIEDAS PER CORE:
1. CORETYPETRANSFORMER:-
 In core-type transformer, the windings are given to a
considerable part of the core.
 The coils used for this transformer are form-wound and are
of cylindrical type.
 Such a type of transformer can be applicable for small sized
and large sized transformers.
 In the small sized type, the core will be rectangular in shape
and the coils used are cylindrical.

2. SHELL-TYPETRANSFORMER:-
 In shell-type transformers the core surrounds a considerable
portion of the windings.
 The coils are form-wound but are multi layer disc type
usually wound in the form of pancakes.
 Paper is used to insulate the different layers of the multi-
layer discs.
 The whole winding consists of discs stacked with insulation
spaces between the coils.

CLASSIFICATION ON THE BASIS OFCOOLING:
1. OIL FILLED SELF-COOLEDTYPE:-
 Oil filled self cooled type uses small and medium-sized
distribution transformers.
 The assembled windings and core of such transformers are
mounted in a welded, oil-tight steel tanks provided with a
steel cover.
 The tank is filled with purified, high quality insulating oil as
soon as the core is put back at its proper place.
 The oil helps in transferring the heat from the core and the
windings to the case from where it is radiated out to the
surroundings.
 For smaller sized transformers the tanks are usually
smooth surfaced, but for large size transformers a greater
heat radiation area is needed, and that too without
disturbing the cubical capacity of the tank.

2. OIL FILLEDWATER COOLEDTYPE:-
 This type is used for much more economic construction of
large transformers.
 The windings and the core are immersed in the oil.
 The cooling coil is mounted near the surface of the oil,
through which cold water keeps circulating. This water
carries the heat from the device.
 This design is usually implemented on transformers that are
used in high voltage transmission lines.
 Such transformers do not require housing other than their
own.This reduces the costs by a huge amount.

CLASSIFICATION ON THE BASIS OFPURPOSE :
1. STEP UPTRANSFORMER
Voltage increases with subsequent decrease in current at
secondary
2. STEP DOWNTRANSFORMER
Voltage decreases with subsequent increase in current at
secondary
3. AIR BLAST TYPE:-
 This type is used for transformers that use voltages below
25,000 volts.
 The transformer is housed in a thin sheet metal box open at
both ends through which air is blown from the bottom to
the top.

CLASSIFICATION ON THE BASIS OFUSE:
1. POWERTRANSFORMER
 high rating
 used in transmission network
2. DISTRIBUTIONTRANSFORMER
 used in distribution network
 lower rating than power transformer
3. INSTRUMENTTRANSFORMER
 used in relay and protection purpose in different
instruments in industries
i. Current transformer ii. Potential transformer

i. CURRENT TRANSFORMER
 Used with low-range ammeters to measure currents
in high-voltage A.C circuits
 Used as a protective device
ii. POTENTIAL TRANSFORMER
 Used to measure high voltage ofA.C circuits
 Used as a protective device

IDEALTRANSFORMER:-
 An ideal transformer is a transformer which has no loses,
i.e. it’s winding has no ohmic resistance, no magnetic
leakage, and therefore no I2R and core loses.
 However, it is impossible to realize such a transformer in
practice.
 Yet, the approximate characteristic of ideal transformer
will be used in characterized the practical transformer

TRANSFORMER EFFICIENCY:-
 The efficiency of a transformer at a particular load and p.f is
defined as the ratio of o/p to i/p.
 The higher the efficiency, the better the system.
η=
Large transformers like distribution transformer cannot be judged by
this efficiency because they are energized all the 24hrs. During light
load or no load condition the core loss occurs throughout the day
and the copper loss occurs only when the transformers are loaded.
Hence the transformers are designed such that the core losses are
very low.The performance of such is compared on the basis of
energy consumed during a certain time period, usually 24hrs.
η= (for 24hrs)

TRANSFORMER EFFICIENCY…
 This efficiency is always less than the commercial
efficiency of a transformer.
 To find this all day efficiency or energy efficiency,
the load cycle is observed i.e. how much and how
long the transformer is loaded during 24hrs.

LOSSES IN TRANSFORMER:-
1.COPPER LOSSES :
 Power is wasted in the form of I2R due to resistance of
windings.
 Its magnitude depends upon current flowing through the coils.
2.HYSTERESIS LOSS :
 Occurs during magnetization and demagnetization ,due to
hysteresis effect some energy losses in the core
 To reduce the loss, the core is made of steel of high silicon
content and is heat treated.
3.EDDY CURRENT LOSS :
It is the current due to the emf generated by leakage flux
By laminating the core, this loss can be reduced.
The lamination can be done with the help of a light coat of core
plate varnish or lay an oxide layer on the surface.

IDEALV/S PRACTICALTRANSFORMER:-
 A transformer is said to be ideal if it satisfies the following
properties, but no transformer is ideal in practice.
1.It has no losses
2.Windings resistance are zero
3.There is no flux leakage
4.Small current is required to produce the magnetic field
 While the practical transformer has windings resistance,
some leakage flux and has lit bit losses.

TRANSFORMER TESTING
 TYPE TEST
 ROUTINE TEST
 SPECIAL TEST
TypeTests
Type test of transformer confirms main and basic design
criteria of a production lot.
 Transformer winding resistance measurement
 Transformer ratio test.
 Transformer vector group test.
 Measurement of SC impedance and load loss (SC test).
 Measurement of no load loss and current (OC test).
 Measurement of insulation resistance.
 Dielectric tests of transformer.
 Temperature rise test of transformer.
 Tests on on-load tap-changer.
 Vacuum tests on tank and radiators.

Routine Tests
Routine tests of transformer is mainly for confirming the
operational performance of the individual unit in a production
lot. Routine tests are carried out on every unit manufactured.
 Routine tests of transformer include all the type tests
except temperature rise and vacuum tests.
 The oil pressure test on transformer to check against
leakages past joints and gaskets is included.

Special Tests
Special tests of transformer is done as per requirement to obtain
information useful to the user during operation or maintenance
of the transformer.
 Dielectric tests.
 Measurement of zero-sequence imp. of 3ф transformers
 Short-circuit test.
 Measurement of acoustic noise level.
 Measurement of the harmonics of the no-load current.
 Measurement of the power taken by the fans and oil pumps.
 Tests on accessories such as buchhloz relay, temperature
indicators, pressure relief devices, oil preservation system,etc.

APPLICATIONAND USES:-
 The transformer used in television and photocopy
machines.
 The transmission and distribution of alternating power is
possible by transformer.
 Simple camera flash uses fly back transformer.
 Signal and audio transformer are used couple in
amplifier.
Today transformers have become an essential part of
electrical engineering

TRANSFORMERS INSTALLEDAT
NALCO
NALCO receives power from odisha grid at 132kV level.
The received 132kV power is stepped down to 33kV and
11kV level at the switchyard, through 5 power
transformers, located at switchyard.
POWERTRANSFORMERS
1. Tr-1101 132/11kV 26.5MVA To alumina plant
3. Tr-1103 132/33kV 10MVA To mines
4. Tr-1104 132/33/11kV 37.5/10MVA To alumina plant

DISTRIBUTIONTRANSFORMER
Tr-2103M 11/33kV 7.5MVA To mines
The 33kV side of Tr-1103 and Tr-2103 feed power to mines
through 33kV SWBD and two 33kV O/H lines to mines. Also
there is an alternate source to mines through one
5MVA,11/33kV transformer at MRS feeding the old 33kV
O/H line.
The 33kV side of Tr-1101, Tr-1102, Tr-1104 and Tr-1105 is
connected to the 11kV switch board located at CDS
through bus duct.

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