distribution transformer testing
TRANSCRIPT
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Testing of Distribution Transformer
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Distribution Transformer
Construction of Transformer
Transformer Name plate details
Routine Test
Factory test
Transformer failure and causes
Type Test
Principle of Transformer
2
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Principle of transformer action
3
A current flowing through a
coil produces a magnetic field
around the coil. The magnetic
field strength H,
required to produce a
magnetic field of flux density
B, is proportional to the
current flowing in the coil.
-
Principle of transformer action
4
A transformer is a static piece of
apparatus used for transferring
power from one circuit to
another at a different voltage,
but without change in frequency.
It can raise or lower the voltage
with a corresponding
decrease or increase of current.
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Distribution Transformer
Construction of Transformer
Transformer Name plate details
Routine Test
Factory test
Transformer failure and causes
Type Test
Principle of transformer actions
5
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CONSERVATOR TANK
TAP SWITCH
HV / LV WINDING
OIL
EXPLOSION VENT
BREATHER
RADIATOR
L.T BUSHING
BOTTOM VALVE
H.T BUSHING
Construction of Transformer
6
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Construction of Transformer
DELTA / STAR
7
.
R
Y
B
y
r
b
n
HV LV
ETH
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6/25/2015 8 Distribution Transformer
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6/25/2015 9 Core and Coil Assembly
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Distribution Transformer
Construction of Transformer
Transformer Name plate details
Routine Test
Factory test
Transformer failure and causes
Type Test
Principle of transformer actions
10
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Transformer Name Plate Details
- Before any testing study of name plate details is must, The HV/LV voltage
,HV/LV current, Size of transformer, Vector group & Impedance volts play
an important roll for calculating test values.
MAKE : ( XYZ )
KVA : (315)
NO LOAD VOLTS HV / LV ( 11000 / 415 ) Volts
FULL LOAD AMPS. HV / LV ( 16.5 / 438.2 ) Amps
FREQUENCY : 50 HZ
TAPPING : No. of Taps :- 7
VECTOR GROUP : Dyn11
TYPE OF COOLING : ONAN
IMPEDANCE VOLTS : 5 %
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Name plate of Distribution transformer-Sample
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Distribution Transformer
Construction of Transformer
Transformer Name plate details
Routine Test
Factory test
Transformer failure and causes
Type Test
Principle of transformer actions
13
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Routine Test
Generally routine test is carried out at stores where we received New /
Recovered transformers from manufacturer and site.
Following Test are perform as routine test.
Insulation Resistance Test
Continuity test
Ratio test (Voltage / Turns ratio)
Short circuit test (Short circuit current)
Open circuit test (Magnetizing current )
Magnetic balance test
Vector Group test
Oil test
14
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Insulation Resistance Test
(IR VALUE)
Insulation resistance test to be carried out by 1 / 2.5 / 5 KV manual or motor driven megger, It gives us the status of insulation of HV
winding and LV winding with respect to earth and between the
winding.
HV WDG. TO EARTH = _____ M
LV WDG. TO EARTH = _____ M
HV WDG.TO LV WDG. = _____ M
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0
M
MEGGER
HV
R
Y
B
TR BODY TR BODY
0
M
MEGGER
LV
R
Y
B
N
Insulation resistance measurement
between LV winding and earth
Insulation resistance measurement
between HV winding and earth
16
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TR BODY
0
M
MEGGER
HV
R
Y
B
LV
R
Y
B
N
Insulation resistance measurement between LV winding and HV
winding
17
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Continuity Test
CONTINUITY TEST CARRIED OUT BY MEGGER OR AVO METER TO CHECK ANY OPEN CIRCUIT FAULT IN THE HV & LV WINDING OF THE
TRANSFORMER.
HV SIDE LV SIDE
RY = _____ rn = _____
YB = _____ yn = _____
BR = _____ bn = _____
VALUE = ZERO ( CONTINUITY O.K )
VALUE = INFINITY ( CONTINUITY NOT O.K)
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R
Y
B
r
y
n
b
-
TR BODY
0
M
MEGGER
LV
R
Y
B
N
TR BODY
HV
R
Y
B
0
M
MEGGER
Continuity test for HV
winding
Continuity test for LV
winding
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Voltage ratio test
Objective:
To check that the ratio of voltages ( in 3-phase transformers, line to line voltages) is as per designed
value in all tap position.
The % Error of the voltage ratio is not more that +/- 0.5 % as per the IS 2026 and IEC 60076
Apparatus:
3 phase supply -415V (Applied to HV side)
Clip on meter for measuring voltage at LV side.
20
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Voltage ratio test
Procedure:
Apply 3 phase 415V supply on HV side and LV side voltage is to be measured.
Output voltage will be measure between phase & neutral (VRN, VYN, VBN). Ratio will be changed in respect to tap positions.
21
Tap position Vrn Vyn Vbn Vry Vyb Vbr
1
2
3
4
5
6
7
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400v AC
supply
ICTP
TR BODY
LV R
Y
B
N
HV
R
Y
B
VOLT-METER
Voltage ratio test
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Voltage ratio test
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HV side 415V
applied
Tap switch
position
LV side voltage
measurement
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Short circuit test
Objective:
To determine the Short Circuit impedance voltage.
To determine the Load losses of the transformer
Short circuit loss = I2R Loss + stray loss
Apparatus:
Voltage injection set (Applied on HV side)
Clip on meter (Measuring current at LV side).
Shorting Link (For passing full load current).
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Short circuit test
Procedure: LV side will be shorted through
shorting link.
Applied the 3 phase voltage on
HV side and increased the voltage
till the full load current passed
through the transformer.
Unbalance current and phase to phase current measure with the help of Clip on meter.
Unbalance current should not be more than 2% of full load current.
Load loss and impedance voltage measured on power analyser. This Load loss measured at Room temperature Converted this loss into 75
Degree C and it should be within the specified limit.
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400v AC
supply
ICTP
TR BODY
LV R
Y
B
N HV
R
Y
B
Short circuit test
Load loss at 75 Degree C = Load loss at RT (A+75) / (A+RT)
Here RT= Room Temperature
A= 235 for CU wound
A= 225 for Al wound
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Open circuit test
Objective:
To know the Excitation losses and currents of Transformer when excited at rated kV at rated Hz
To determine the No load losses(Core loss) of the transformer
To check healthiness of winding and stampings.
No load loss = hysteresis loss + eddy current loss
Apparatus:
Voltage injection set (Applied on LV side)
Clip on meter for measuring no load current at LV side.
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Hysteresis Loss
28
when a magnetic field is applied all the
grains of the magnetic material will
orient in the direction of magnetizing
force. In another cycle this grains will
orient in opposite direction in the
direction of magnetizing force. The
energy required to change the
orientation of the magnetic grains in the
direction of the magnetic field is lost in
the form of heat. This loss is called
hysteresis loss.
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Eddy current Loss
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Eddy Current Loss:
When an alternating magnetic flux is applied to the iron
core small emf will be induced due to change in flux
linkage. This induced emf will cause small circulating
current s called eddy currents. Eddy current flowing
through the material causes I2R losses in the material.
In order to reduce the Eddy Current loss:
Use of Material having high electrical resistivity:
By using superior grain orientation CRGO steel will have
higher electrical resistivity. Thus eddy current loss can
be reduced.
Lamination Cores are used:
By using thin laminations the core thickness is reduced
so eddy current losses are reduced. So CRGO steel
laminations are used as a core material.
Insulation between laminations:
Oxide coating is provided for CRGO laminations to
reduce eddy current losses.
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Open circuit test
Procedure:
Rated voltage applied on LT side
of distribution transformer for
energizing transformer.
No load current measured by
clip on meter and no load loss
measured by power analyzer.
No load current should not be
more than 3% of full load current.
Note: Nobody can go closer to HV side
because it is subject to 11KV.
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TR BODY
LV R
Y
B
N
HV
R
Y
B
400v AC
supply
ICTP Open circuit test
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Rating 1 star 2 star 3 star 4 star 5 star
KVA Max Losses
at 50% (Watts)
Max Losses at 100% (Watts)
Max Losses at
50% (Watts)
Max Losses at
100% (Watts)
Max Losses at
50% (Watts)
Max Losses at
100% (Watts)
Max Losses at
50% (Watts)
Max Losses at
100% (Watts)
Max Losses at
50% (Watts)
Max Losses at
100% (Watts)
16 200 555 165 520 150 480 135 440 120 400
25 290 785 235 740 210 695 190 635 175 595
63 490 1415 430 1335 380 1250 340 1140 300 1050
100 700 2020 610 1910 520 1800 475 1650 435 1500
160 1000 2800 880 2550 770 2200 670 1950 570 1700
200 1130 3300 1010 3000 890 2700 780 2300 670 2100
Star Rating of Transformer(BEE)
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BEE Star Labeling
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Full load current and loss of different rating
transformers
KVA
HV
(Amp)
LV
(Amp)
NO LOADLOSS
( Watts)
LOAD LOSS
(Watts)
160 8.4 222.6 300 1600
315 16.5 438.2 515 2750
630 33.1 876.5 800 4700
990 52 1377 1250 6200
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Magnetic Balance Test:
rn yn bn
rn= 240 240 156 84
yn= 240 120 240 120
bn =240 84 156 240
Applied 240V on LV side and voltage measured on respective LV terminals
as under.
Division should 65:35 between central and the other extreme limb if one
of the extreme limbs is excited and is 50:50 for central limb excitation
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Break down voltage test of Oil
Transformer oil is used insulation as well as cooling
purpose.
BDV tester ranging from 0-100KV used for test.
Gap between two electrodes must be maintain 2.5mm.
BDV of new insulating oil
Should be more than 60KV.
37
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Acidity test of Oil
In this test we will measure the value of free carbonic and non-carbonic acid in oil and this will be measured
with the help of acidity testing kit.(mgKOH/gm)
Acidity must be less than 0.03 for new insulating oil.
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Distribution Transformer
Construction of Transformer
Transformer Name plate details
Routine Test
Factory test
Transformer failure and causes
Type Test
Principle of transformer actions
39
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Factory Test
In addition to routine test some more test are carryout at factory, This
type of test required some specific testing instruments and testing
facilities, even through some of the test carryout at site also.
Winding resistance test
Vector group test
Separate source voltage test
Temperature rise test
Induced overvoltage test
40
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Distribution Transformer
Construction of Transformer
Transformer Name plate details
Routine Test
Factory test
Transformer failure and causes
Type Test
Principle of transformer actions
41
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Over and above routine test some important test are carried out at
factory or laboratory like ERDA & CPRI, this type of test required
some special testing instrument and testing facility.
Impulse Voltage Test - 95KVp
Short circuit withstand test - 18.4 KA for 3 sec
Partial discharge test
Type Test
42
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Distribution Transformer
Construction of Transformer
Transformer Name plate details
Routine Test
Factory test
Transformer failure and causes
Type Test
Principle of transformer actions
43
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Failure & Causes
Insufficient Oil level.
Seepage of water in oil.
Prolonged Over loading.
Single Phase loading.
Unbalanced loading.
Faulty Termination (Improper sized lugs etc)
Power Theft.
Prolonged Short Circuit.
Faulty operation of tap changer switch.
Lack of installation checks.
Faulty design
Poor Workmanship Improper formation of core.
Improper core bolt insulation.
Burr to the lamination blades
Improper brazing of joints.
Burr /sharp edges to the winding conductor.
Incomplete drying.
Bad insulation covering.
Insufficient cooling ducts in the winding.
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Failure & Causes
Faulty design
Poor Workmanship
Improper formation of core. Improper core bolt insulation. Burr to the lamination blades Improper brazing of joints. Burr /sharp edges to the winding conductor. Incomplete drying. Bad insulation covering. Insufficient cooling ducts in the winding.
Bad Quality of raw material.
Transit damaged transformers. After failure , transformer is removed and replaced with
new/repaired one without removing the cause of failure which results in immediate or short time failure.
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Thank You