mvvnl transformer test report
TRANSCRIPT
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A Di
10 M
M/s
gnostic Test Report
On
A Power Transformer
At
PPTCL, Lucknow
July 2013
Submitted By
tekpro Technologies Pvt. Ltd.
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GENERAL SAFETY
Safety is right at Mtekpro Technologies Pvt. Ltd., not a privilege! Comply with all the safety
regulations and recommendations of the equipment manufacturers and plant operators.
A LIFE LOST HAS UNRECOVERABLE DAMAGES! So take following Precautions;
Ensure that the DEVICE UNDER TEST (DUT) is de-energized/isolated from all sources.
Ensure that safety grounds are put before making any connections to the DUT.
Ensure that connections to the supply sources for tests are tight and FUSES/MCB of adequate
rating is used. The connection should preferably be taken from metal clad switches instead of
plug points. Supply cables should not lie on ground but should be suitably supported.
Instrument should be arranged at height convenient for operation
DUT and test area should be cordoned off. Only authorized persons should enter the area.
Ensure that necessary authorization for testing the equipment has been obtained as per safety
tagging procedure.
Ensure that all connections to the equipment are tight. Ground connections should be neat if
proper size. Cleaned and properly tightened.
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Index
Sr. No. Contents Page Number
01 Executive Summary 01 - 02
02 Partial Discharge Measurement Introduction 03 - 05
03 Partial Discharge Measurement Report 06
04 Transformer Turns Ratio Introduction 07 - 09
05 Turns Ratio Report 10
06 Winding Resistance Measurement Introduction 11 - 13
07 Winding Resistance Measurement Report 14 - 15
08 Physical Observation 16
09 Service Brochure
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Executive Summary on Condition Assessment
Test of 10 MVA Power Transformer
1. Introduction:
M/s MVVNL, Lucknow invited M/s Mtekpro Technologies Pvt. Ltd., New Delhi to demonstrate the
testing equipments for Electrical Power System. M/s Mtekpro Technologies Pvt. Ltd., New Delhi has
deputed their Condition Assessment Team on 25th July 2013 to M/s MVVNL, Lucknow to demonstrate
the Condition Assessment Equipments at Railway Power House. During the mobilization for
Demonstration Transformer assessment testing was executed in the presence of M/s MVVNL, Lucknow
officials.
2. Scope of Work:
In this visit at M/s MVVNL, Lucknow following Testings are done for demonstration:
2.1 10 MVA, 33/11 kV Power Transformer
2.1.1 Partial Discharge Measurement
2.1.2 Transformer Winding Turns Ratio Test
2.1.3 DC Winding Resistance Measurement
3. Detailed Analysis of the Report:
3.1 Partial Discharge Measurement was done on the Power Transformer by Acoustic Sensor Method.
Measurement was done on all directions of Transformer tank body on various locations.
Result does not show any critical partial discharge through the Winding and Insulating Oil. For more
detailed report please refer partial discharge report on page number 06.
3.2 As Transfomer Tap Changer was damaged / not in operating condition turns ratio measurement was
done only on one tap which was also not accessible. And the same was informed to M/s MVVNL,
Lucknow officials to take necessary action for changing or repairing of Tap Changer.
Winding Turns ratio measurement between the Phases are identical. In the absence of Tap position
we are unable to check the ratio error of the winding.
If transformer will run in this condition for any more time their may be possibility to burn down due
to contact loss and heating in Tap Changer. For detail report on Winding Turns Ratio Measurement
refer page number 10. 1
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3.3 Transformer winding resistance measurement was done by injecting DC 40 A current. The winding
resistance measurement between Y and B phases are approximately same while R phase resistance
differs from them. This might be possible due to loose contacts in tap connections.
As Tap changer was damaged resistance measurement was possible at only one tap.
The winding resistance measurement on LT 11 kV side was found satisfactory. For detail report refer
page numbers 14 and 15.
4. Observations & Recommendations:
4.1 During the Testing of Transformer oil leakages are observed on entire tank body of the transformer
and the same was informed to M/s MVVNL, Lucknow officials. This needs to be rectified as soon as
possible.
4.2 The Partial Discharge measurement does not show any discharge abnormal condition. It is
recommended to check PD after Six month or One year. It is also require to employ alternate
technologies for PD measurement.
For demonstration purpose we have carried Acoustic Sensor based technologies, while we have
alternate technologies like ULD-40 & HFCT are available for PD measurement.
4.3 The Transformer is running with damaged tap changer from many years. That needs to be changed
or repaired as soon as possible to increase the life and smooth operation of the transformer.
The Winding Resistance and Turns Ratio Measurement was done on only one Tap it is
recommended that after rectification of tap change these tests must be repeated.
4.4 Transformer oil BDV needs to be checked and if it falls below the standard value then needs to be
filtered to make it free from dust and moisture.
4.5 M/s Mtekpro Technologies Pvt. Ltd., New Delhi also recommends M/s MVVNL, Lucknow to make
complete assessment test on transformers and associated switchyard equipments to reduce the
chances of breakdown during its operating period Please refer page number 17 & 18.
4.6 For Condition Monitoring and Diagnostic Testing (CMD) details refer our service brochure.
All testings mentioned in brochure needs to be done once in a year or after a interval of two year to
ensure the health condition of power equipments. For Power Transformer other recommended tests
to chek the health of transformer refer page numbers 17 and 19. 219.
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Measurement At Channel 1 (mV) Channel 2 (mV) Channel 3 (mV)
Position 1 33.9 32.8 35.3
Position 2 41.2 38.4 33.6
Measurement At Channel 1 (mV) Channel 2 (mV) Channel 3 (mV)
Position 1 15.8 13.9 18.4
Position 2 17.4 18.4 21.8
Measurement At Channel 1 (mV) Channel 2 (mV) Channel 3 (mV)
Position 1 38.8 43.1 44.7
Position 2 42.8 39.7 45.7
Measurement At Channel 1 (mV) Channel 2 (mV) Channel 3 (mV)
Position 1 10.3 12.1 9.7
Position 2 16.6 16.2 12.4
Open Side PD Measurement
Transformer Partial Discharge Test Report
HT Side (33kV) PD Measurement
LT Side (11kV) PD Measurement
OLTC Side PD Measurement
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Remarks: For details on report refer executive summary clause
number 3.1 and for recommendations clause number 4.2.
Testing Engineer
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2.0 TRANSFORMER TURNS RATIO TEST
2.1 SCOPE
The function of a transformer is to transform power from one voltage level to another .The ratio
test ensures that the transformer windings have the proper turns to produce the voltages required.
2.2 INSTRUMENTS
220V ,50H Turns ratio tester with a capability of measuring ratios from 0.8 to 15,000,three
phase Excitation current ,Phase angle reading and can measure the turns ratio of phaseshifting
transformer.
Make-VANGURD, USA
Model-ATRT-01B
2.3 PREPARATIONS, PRECAUTIONS & WARNINGS
The voltages should be applied only HV winding in order to avoid unsafe voltage.
2.4 TEST PROCEDURE
The turns ratio is measure of the RMS voltage applied to the primary terminals to the RMS
voltage measured at the secondary terminals.
R= Np / NsWhere,
R-Voltage ratio
Np- Number of turns at primary winding.
Ns- Number of turns at secondary Winding.
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2.5 EVALUATION OF TEST RESULTS AND ACCEPTANCE LIMIT
The IEEE standard (IEEE Standard 62) states that when rated voltage is applied to one winding
of the transformer, all other rated voltages at no load shall be correct within one half of one
percent of the nameplate readings. It also states that all tap voltages shall be correct to the
nearest turn if the volts per turn exceed one half of one percent desired voltage .The ratio test
verifies that these conditions are met.
The IEC60076-1 standard defines the permissible deviation of the actual to declared ratio as
follows:
Principal tapping for a specified first winding pair: the lesser 0.5% of the declared voltage ratio
or 0.1 times the actual short circuit impedance. Other taps on the first winding pair and other
winding pair must be agreed upon, and must be lower than the smaller of the two values stated
above.
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Deviations in turns ratio readings indicate problems in one or both windings .In particular ,the
TTR test is useful for identifying shorted turns or open circuits in the windings, incorrect
winding connections ,and other internal faults or tap changer defects. If possible, the ratio at
each tap setting should be checked against the nameplate ratio for each tap.
Measurements are typically made by applying a known low voltage across the high voltage
winding so that the induced voltage on the secondary is lower, thereby reducing hazards while
performing the test .For three phase delta/wye or wye/delta transformer, a three phase
equivalency test is performed, i.e. the test is performed across corresponding single winding.
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Remarks: For details on report refer executive summary clause number 3.2
and for recommendations clause number 4.3.
Testing Engineer
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3.0 WINDING RESISTANCE MEASUREMENT
3.1 SCOPE
Transformer winding resistance is measured in the field in order to check for any abnormalities
due to loose connections, broken strands and high contact resistance in tap changers as pre
commissioning checks and compare the measured values with factory test values.
3.2 PREPARATION, PRECAUTIONS & WARNINGS
As the transformer winding have low resistance, the measurement has to be carried out with the
help of Kelvin double bridge/Transformer Ohmmeter. To reduce the high inductive effect it is
advisable to use a sufficiently high current to saturate the core. This will reduce the time
required to get a stabilized reading. It is essential that a temperature of the winding be
accurately noted because resistance is temperature sensitive.
Care also must be taken to ensure that direct current circulating in the winding has settled down
before the measurement is done. In some cases this may take several minutes depending upon
the winding inductance.
3.3 PROCEDURE
Winding resistance measurement are performed with low-resistance ohmmeter. For a three
phase Wye-connected transformer, the resistance is measured for each phase-to-neutral
winding: Note that for delta-connected transformer, the measured resistance for each phase is
composed of parallel combination of the winding under test and the series combination of the
remaining winding .It is therefore recommended to make three measurements for each phase-
to-phase winding in order obtain the most accurate results. It is also recommended to allow the
transformer to sit de- energized until temperatures are equalized (difference between top andbottom temperature does not exceed 5CANSI / AIEEE C57.12.90) before making resistance
measurements. 11
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According to IEC 60076-1, in order to reduce measurement errors due to changes in
temperature, some precautions should be taken before the measurement is made.
For Star connected winding the neutral brought out, the resistance shall be measured between
the line and neutral terminal and average of three sets of reading shall be the tested value. For
Star connected auto transformers the resistance of the HV side is measured between HV
terminal and IV terminal, then between IV terminal and the neutral. For Delta connected
windings, such tertiary winding of auto-transformers measurement shall be done between pairs
of line terminals and resistance per winding shall be calculated as per the following formula:
Resistance per Winding = 1.5 X Measured Value
For Dry type transformers, the transformer shall be at rest in a constant ambient temperature for
at least three hours.
For Oil immersed transformers, the transformers should be under oil and without excitation for
at least three hours. In addition, it is important to ensure that the average oil temperature
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(average of the top and bottom oil temperatures) is approximately the same as the winding
temperature.
In order to diagnose possible problems, the measured results are compared to the factory
values, values of other phases of the same transformer, or sister units, if available. Before
making such comparisons, the resistance has to be converted to a common temperature base of
75C or 85C, depending on what is reported on the transformer factory test sheet.
The corrected resistance is calculated as:
Rs = Rmeas X
Where,
Rmeas = Measured Winding Resistance
Rs = Corrected Winding Resistance = Reference Temperature at which the resistance is corrected (75C)
= Temperature at which the resistance is measured (25C)
= 234.5 for copper windings / 225C for Al windings
Consistency in measurements and record keeping are the keys to making the proper analysis
using this test. If the unit has a Tap Changer, it is important to compare resistances for the same
tap position. The contact resistance of other tap positions can be investigated by moving taps
and repeating the measurements.
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Remarks: For details on report refer executive summary clausenumber 3.3 and for recommendations clause number 4.3.
Testing Engineer
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Remarks: For details on report refer executive summary clausenumber 3.3 and for recommendations clause number 4.3.
Testing Engineer
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A-1 Electrical Tests
1. Turns - Ratio Test
2. Insulation Resistance Test
3. Polarization Index (PI) and Dielectric Adsorption Test
4. Capacitance and Tandelta Measurement for winding & Bushing
5. Impedance Measurement
6. Magnetizing Current Test7. Core Ground Test
8. Magnetic Balance Test
9. Vector Group Check
10. Winding Resistance Test
A-2 Oil Test
1. Dielectric breakdown
2. Neutralization number
3. Interfacial tension
4. Specific gravity
5. Colour and visual condition6. Water content
7. Power factor
8. PCB
9. DGA
10. Furan
11. Inhibitors
12. Degree of polymerization of paper
A-3 Transformer Visula Examination
1. Infrared thermography
2. Main tankstructure/leak3. Radiators and cooling fans
4. Conservator Tank
5. Tap - Changer contacts / Control Mechanism
6. Gas detector and sudden pressure relays
7. Pressure relief device
Power Transformer Routine TestingM/s Mtekpro Technologies Pvt. Ltd. Performs industry standard inspection Testing including:
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8. Bushing Insulator, gasket, leak
9. Oil and Winding temperature gauges
10. High and low voltage bushings
11. Valves and Piping
12. Control, VT and CT wiring
A-4 Tap-Changer Test
1. Tap position Indicators
2. Gaskets and seals
3. Current carrying contacts
4. Drive Mechanism
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B-1 Dielectric Frequency Response (DFR)
Dielectric Frequency Response Testing is performed on the transforme primary to
estimate the moisture content of insulation. DFR is alos used to check the electical
intergrity of the transformers. DFR assesses the insulation of High Voltage (HV) to tank,
Low Voltage (LV) to core, and insulation between HV and LV. The transformer must be
offline and preferably disconnected from all connection hardware such as disconnect
switches, buses, cables , and surge arrestors.
In the DFR test, , by applying a variable frequency voltage between the HV and LV
winding , the current is recorded by a high resolution electrometer. Some calculation is
required to extract the dissipation factor plot versus applied frequency. DFR testing can
detect paper moisture, insulation contamination, series contact issues and most
abnormalities insided the winding insulation and oil.
B-2 Frequency Response Analysis (FRA)
Kinectrics, (formerly the Ontario Hydro R 7 D Division ) pioneered FRA, which is a
technique currently being used by several utilities to detect winding damage and winding
losseness in power transformers. FRA is performed off-line . It is recommended that this
test be performed at least once to extract the baseline transfer function of the winding ,
which is essential for future comparision. FRA measures the mutual transfer function of
the transformer winding in a frequency range of 10 Hz to 2 MHz.
B-3 Frequency Response Stray Losses (FRSL)
FRSL is used to detect short strands within a conductor . In the FRSL test, the AC
resistance of the windings is measured from 20 Hz to 4000 Hz . As the frequency
increases the skin effect becomes more pronounced, resulting in higher resistance. The
AC resistance of 3 phases is compared to identify the faulty phase.
Advanced Diagnostic Testing
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THANK YOU!www.mtekpro.com
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