MVVNL Transformer Test Report

7/27/2019 MVVNL Transformer Test Report

1/24

A Di

10 M

M/s

gnostic Test Report

On

A Power Transformer

At

PPTCL, Lucknow

July 2013

Submitted By

tekpro Technologies Pvt. Ltd.


2/24

A

10

Ph:

A DIAG

0 MVA

U

M

B 22

011 4617 3

GNOS

A POW

UPPTCJU

/s Mtekp

9, LGF, Gre

333 / Fax:

STIC TON

WER TAT

CL, LUULY 2

Submitt

ro Techn

ter Kailash

11 4182 5

ww.mtekp

TEST R

TRANS

UCKNO013

d By

logies P

1, New D

62 / info@

ro.com

REPO

SFORM

OW

t. Ltd.

lhi 110048

mtekpro.c

ORT

MER

m / Web:

.


3/24

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.

Mtekpro Technologies Pvt. Ltd.

.


4/24

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


.


5/24

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


.


6/24

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.


.


7/24


.


8/24


.


9/24

.


.


10/24

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


Position 1 15.8 13.9 18.4

Position 2 17.4 18.4 21.8


Position 1 38.8 43.1 44.7

Position 2 42.8 39.7 45.7


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

6

Remarks: For details on report refer executive summary clause

number 3.1 and for recommendations clause number 4.2.

Testing Engineer


.


11/24

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.

7


.


12/24

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.

.

8


.


13/24

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.

9


.


14/24

Remarks: For details on report refer executive summary clause number 3.2

and for recommendations clause number 4.3.

Testing Engineer


.


15/24

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


.


16/24

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

12


.


17/24

(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.

13


.


18/24

Remarks: For details on report refer executive summary clausenumber 3.3 and for recommendations clause number 4.3.

Testing Engineer


.


19/24

Remarks: For details on report refer executive summary clausenumber 3.3 and for recommendations clause number 4.3.

Testing Engineer


.


20/24


.


21/24

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:

17


.


22/24

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

18


.


23/24

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

19


.


24/24

THANK YOU!www.mtekpro.com

.

Documents

MVVNL Transformer Test Report