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Presentation on Transformer
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MAJOR TOPICS
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INTRODUCTION
Transformer is a device that
Transfer electrical power from one circuit to
another
It does so without a change of frequency
It accomplishes this by electromagnetic
induction
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Working Principle of
Transformer
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Classification of Transformer
1.Step Up Transformer
2.Step Down Transformer
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Step Up Transformer
If the secondary winding has more
no. of turns than primary winding,
then secondary voltage is higher
than primary voltage and
transformer is called step uptransformer
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Step Down Transformer
If the secondary winding has lesser
no. of turns than primary winding,
then secondary voltage is lowerthan primary voltage and
transformer is called step up
transformer
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CONSTRUCTION
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Type of Transformer
Core Type Transformer
Shell Type Transformer
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Core Type Transformer
Core type transformers the winding
surrounds a considerable part of the
winding. The coils used are formwound and are of the cylindrical type.
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Shell Type Transformer
In Shell type transformers the core
surrounds a considerable portion of
the winding. In this type the coils arealso form wound but
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Major Parts of Transformer
ransformer Tank
rimary & Secondary Winding
agnetic Core
ap Changer
onservator
adiators
ilica Gel Breather
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Primary & Secondary Windings
Primary Winding: -
The winding to which the input voltage is
applied is called the primary winding.
Secondary Winding: -
The winding to which the load is connected orwhich delivers output is called secondary
winding.
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Magnetic Core
Magnetic core made of thinsilicon steel laminations . Inorder to reduce the eddycurrent losses, these
laminations are insulatedfrom each other by thin layersof varnish. The verticalportions of the core are calledlegs or limbs and the top andthe bottom portion are calledthe yokes
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Conservator
It is a large cylinder connected bypipe to the transformer main
tank. Transformer oil is filled up
to the certain level in the
conservator. Remaining upperportion is filled with air. The
conservator volume is used for
expansion of oil during higher
loads. Communication of the airbetween top of the conservator
and outside air is through the
breather.
Conservator tank
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Conservator
Conservator are of two type: -
Conventional Conservator
Conservator with Rubber Air Bag
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Silica Gel Breather
It is installed in a pipe from the
conservator. Air is breathed
during the load cycle through
the breather. Silica gelbreather provides moisture
free air to the conservator
tank. Silica gel crystal are dark
blue in color when dry.Silica Gel Breather
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Tap Changer
Tap Changer is generally
provided on the High
Voltage side of the
winding of transformer. Tap changers are used
to maintain thesecondary voltage
reasonably constant atthe users end.
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Typpes of Tap Changer
Off Circuit Tap Changer: -
Designed to operate with Transformer out ofcircuit.
Used for seasonal voltage variations.
Consists of three parts: Live part connected to
winding ; operating handle drive brought out oftransformer for operating the switch & linkconnection between the above two parts.
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On Load Tap Changer: -
Designed to operate with Transformer in circuit.
Used for daily or short period voltage variations
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Buchholz Relay
Gas & oil operatedinstrument which detects
low oil level, formation of gas
or development of sudden
pressure inside the oil filledtransformer.
Gives both the alarm &
tripping signal depending
upon the oil level or amount
of gas formed.
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Bushings
The Function of abushing is to provideinsulating support to aconductor passing
through earth tank.
Bushing is used when aconductor is taken outthrough metallic tank ora wall.
Is made of single pieceporcelain.
Bushings
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Marshalling Box
This Box is provided with eachlarge transformer and placedon the side of the transformerand this enclosure is
completely weather proof. All control cable and power
cables for fan control and andauxiliary supply switchgear etc.
are via marshalling box and italso houses the oil andwinding temp. indicators.
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Magnetic Oil Level Indicator
This is direct oil level indicating
device provided on conservator. The center of the dial is normally
marked with a temp. 25 degreeCelsius. High & low level points are
also marked to follow level changesas oil expands & contracts withtemp. changes.
The low oil contacts provided can
be used for automatic alarm ortripping when the oil level in theconservator falls to a low level.
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Oil & Winding Temp. Indicator
Oil Temp. Indicator: -
The thermocouple is placed in the pocket
provided with the tank near hot oil &thermocouple leads are connected to oil
temperature indicator placed in marshalling
box.
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Winding Temp. Indicator: -
winding temperature indicator placed in themarshalling box gets input for measurement
from
1. Thermocouple placed in the pocketprovided with the tank near hot oil
2. CT secondary which measures the current
in windingThe indicator is provided with alarm &
tripping contacts
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Radiators
Provides cooling to the
transformer oil. Oil is
circulated through the
radiators in whichcooling can be assisted
by a blast of air
provided by fans. This
cycle is continuouslyrepeated
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Types of Cooling of Power
Transformer
O.N.A.N Oil Natural Air Natural
O.N.A.F Oil Natural Air Forced
O.F.A.F Oil Forced Air Forced
O.F.W.F Oil Forced Water Forced
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DOUBLE DIAPHRAGM EXPLOSION
VENT Prevents damage to transformer tank by releasing
any excess pressure that is generated inside thetank.
Consists of a bent pipe with aluminum diaphragms atboth ends. A protective wire mesh is fitted at theopening of the tfr. Also a wire mesh is provided atupper end to prevent upper diaphragm frommechanical damage.
Near the lower end there is a small oil level indicator
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OPERATION
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LOSSES IN A TRANSFORMER
Mainly two types of losses- Copper loss & Iron
loss.
Copper loss is directly proportional to square
of load on the transformer.
Iron loss consists of
Eddy current loss.
Hysteresis loss
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Eddy Current Losses
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Why Transformer rating in KVA
Because Copper loss of Transformer depends
upon current and Iron loss on voltage. Hence,
total transformer loss depends on volt-
ampere (VA) and not on phase angle betweenvoltage and current i.e. it is independent of
load power factor. Hence rating of
transformer is in KVA and not in KW.
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VOLTAGE REGULATION
It is defined as change in magnitude of the secondaryterminal voltage, expressed as a percentage of thesecondary rated voltage, when load at a given powerfactor is reduced to zero, with primary applied
voltage held constant.
If V1 is secondary terminal voltage at no load
V2 is secondary terminal voltage at full load %regulation = (V1 -V2 )*100/ V1
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This change in secondary terminal voltage
with load current is due to leakage
impedances of the transformer. Themagnitude of this change depends on the load
power factor, load current, total resistance &
total leakage reactance of the transformer. Distribution transformers should have good
voltage regulation so that voltage at the
consumers premises doesnt vary widely asthe load changes.
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EFFICIENCY
Efficiency of Transformer is defined as Ratio of
output power to input power.
Efficiency = Output/Input
= (Input-Losses)/Input
Efficiency of power & distribution transformers isvery high( 95% to 99% ).
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Condition of Maximum Efficiency
Efficiency of a Transformer is maximum when
Copper Losses = Iron Losses
The above condition occurs at
About half the rated load in distribution
transformers
Near rated load in power transformers
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All Day Efficiency
Transformers used for supplying lighting have theirprimary energized all the twenty four hours,although their secondary supplies no load much ofthe time. Hence the Iron losses occurs whole of the
day and copper losses when loaded. Theperformance of such transformer is judged by all dayefficiency (for a 24 hours)
%efficiency(All Day)
= Output in KWH/Input in KWH (For 24 Hours)
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Difference Between Distribution
Trf & Power Trf.Distribution Trf.
The maximum efficiency of adistribution trf may occur atabout half the rated load oftrf.
The efficiency of distribution
trf is usually measured as Allday efficiency as load on
these trf varied b/w widelimits during 24 hours of aday.
Power Trf.
The maximum
efficiency of a power trf
occur at or near its fullload rated KVA.
Efficiency of power trf is
measured as
output/input
DISTRIBUTION
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DISTRIBUTION
TRANSFORMERSPOWER TRANSFORMERS
Distribution trf are thosewhich change the voltage
to a level suitable for
utilization purposes at the
consumers premises.
Distribution trf are
designed to have very low
iron losses.
Distribution trf have less
efficiency than power trf.
Power trf. are those which areused at sending & receiving
ends of a long, high voltage
power transmission line for
stepping up or stepping downthe voltage.
Power trf have more iron
losses.
Power trf have more efficiency.
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Maintenance
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Maintenance Schedule
Sr.
No
Frequency of
operationItem to be inspected Inspection
1. Hourly
Winding temperature.
Oil Temperature
Load in Ampere
Voltage
Check that
temp. rise is
reasonable
Check against
the rated.
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Maintenance Schedule
Sr.
No
Frequency of
operation Item to be inspected Inspection
2. Daily
Oil level in
transformer and on
load tap changer
Oil level in
transformer bushing
Dehydrating Breather
Check against
the oil level
Do
Check the colourof the silica gel
& oil level in oil
cup
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Maintenance Schedule
Sr.No
Frequency ofoperation
Item to be inspected Inspection
3. Quarterly
Bushing
Oil in transformer
and OLTC
OLTC driving
mechanism &
Automatic control
Examine for any
crack or dirtdeposit
Check the
dielectric strength
of the oil
Lubricate the
bearing & check
the all circuits
including Limit
switches
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Maintenance Schedule
Sr.No
Frequency ofoperation
Item to be inspected Inspection
4. Yearly
Oil in transformer
Insulation Resistance
Value
Temperature
Indicator
Check for acidity
and sludge.
Compare with the
value at the time
of commissioning
Pocket holdingthermometer
should be checked
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Maintenance Schedule
Sr.No
Frequency ofoperation
Item to be inspected Inspection
4. Yearly
4. Dial type oil Gauge
Relays, alarms, their
circuits etc.
Earth resistance
Check pointer for
freedom
Check the relays
and alarm contactsand their
operation.
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Testing
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Ratio Test
This test is conducted by applying a single
phase 230 V supply on the High Voltage Side
winding and measure the voltage on Low
Voltage Side winding. The Ratio should bechecked at all tap positions.