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2. DPL Power Transformer(Unit-
4)
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3. Transformer Ratings In
DPL
Generating transformer for Unit(1&2)
KVA Rating 37500KVA
HV/LV (KV) 132/6 KV
Impedance Voltage at 75 c 11.10% at above ratings
Connection Symbol Ydelta1
Frequency 50Hz
Total Weight 66tones
Quantity of Oil(gallons) 4048
Manufactured by English Electric Co Ltd
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4. Generating Transformer For Unit (3&5)
MVA Rating(MVA) 42.5 59.5 85
HV/LV Rating 132/11 KV
HV/LV(line current) 372.22/4679.3(amps)
Connection Symbol Ydelta1
Frequency 50Hz
Temp Rise Oil(deg Celsius) 40
Temp Rise Winding(deg
55
Celsius)
Manufactured By BHEL
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5. Generating Transformer for Unit 4
KVA Rating (KVA) 85000
HV/LV(KV) 132/11
HV/LV(line current) 372/4680 amps
Connection Symbol Ydelta1
Frequency 50Hz
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6. What is a
Transformer???
A transformer is a static Device which
consists of two or more stationary
electric circuits whose
main purpose of transferring
electrical power by
magnetically link without
changing the frequency.
The Transformer consists of
several parts:-
1. Core
2. Coil
3. Bushings
4. Tap Changer
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7. Transformer Equation
The Simple Transformer
Equation states:-
V2/V1=N2/N1=I1/I2
Where V2,N2 And V1,N1 are
the terminal potential
difference and number of
turns in secondary and
primary sides respectively.
Whereas I1 and I2 are the
current flowing in primary and
secondary sides of the
transformer.
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8. Types of Transformer
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Step UP Transformer :
A transformer in which N2>N1 and which converts low
voltage to high voltage.
Step DOWN Transformer :
A transformer in which N1>N2 and which converts high
voltage to low voltage.

9. Transformer Core
Transformer core is a
closed magnetic circuit
through the mutual flux
i.e. the flux which links with
both the winding passes.
The core material and the
construction of the core
will be such that
magnetizing current and
core losses are minimum.
The core of the
transformers are laminated
in order to reduce eddy
current losses.
The laminations are 0.33-
0.5mm thick.
These laminations are
made of transformer
graded steel containing 3-
5% silicon
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10. Transformer Windings
The conducting material used
for the windings depends
upon the application, but
in all cases the individual
turns must be electrically
insulated from each other
to ensure that the current
travels throughout every turn.
High-frequency transformers
operating in the tens to
hundreds of kilohertz often
have windings made of
braided Litz wire to minimize
the skin-effect and proximity
effect losses.
Large power transformers use
multiple-stranded conductors
as well, since even at low
power frequencies
non-uniform distribution
of current would otherwise
exist in high-current windings.
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11. Transformer Bushing
The non-faded portion in
the picture on the left
hand side is the
bushings. In electric
power, a bushing is
an insulated device that
allows an electrical
conductor to pass safely
through a (usually)
earthed conducting
barrier such as the wall of
a transformer or circuit
breaker.
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12. A bushing must be
designed to withstand
the electrical field
strength produced in the
insulation, when any
earthed material is
present. As the strength
of the electrical field
increases, leakage paths
may develop within the
insulation. If the energy
of the leakage path
overcomes the dielectric
strength of the insulation,
it may puncture the
insulation and allow the
electrical energy to
conduct to the nearest
earthed material causing
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Transformer Tap-
Changer
Tap changer is
connection point
selection mechanism
along power
transformer winding that
allows a variable number
of turns to be selected in
discrete steps. A
transformer with a
variable turns ratio is
produced, enabling
stepped voltage regulati
on of the output. The tap
selection may be made
via an automatic or
manual tap
changer mechanism.

14. Transformer Construction
Core Type Transformer Shell Type
Transformer
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15. Core Type Transformer
In the core type of
transformer, the primary
and secondary windings are
wound outside and
surround the core ring. In
the core type transformer
construction, one half of
each winding is wrapped
around each leg (or limb) of
the transformers magnetic
circuit. In the core type
transformer flux flowing
through the frame is Φ.
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16. Shell Type Transformer
In the shell type transforme, primary
and secondary windings are wound
on the same centre leg or limb which
has twice the cross-section of the
other two legs. The advantage here
is that the magnetic flux has two
closed magnetic paths to flow
around external to the coils on both
left and right hand sides before
returning back to the central
coils.This means that the magnetic
flux circulating around the outer
limbs of this type of transformer
construction is equal to Φ/2.
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17. Transformer Protection
In the field of electric power
distribution and
transmission, a Buchholz
relay is a safety device
mounted on some oil-filled
power transformers
and reactors, equipped with
an external overhead oil
reservoir called
a conservator. The
Buchholz Relay is used as
a protective device
sensitive to the effects
of dielectric failure inside
the equipment.
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18. Silica Gel Container
Most of the power
generation
companies use silica
gel breathers fitted to
the conservator of oil
filled transformers.
The purpose of these
silica gel breathers is
to absorb the
moisture in the air
sucked in by the
transformer during
the breathing
process.
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19. What is Transformer
Breathing?
When load on transformer increases or
when the transformer under full load, the
insulating oil of the transformer gets
heated up, expands and gets expel out
in to the conservator tank present at the
top of the power transformer and
subsequently pushes the dry air out of
the conservator tank through the silica
gel breather. This process is called
breathing out of the transformer.
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