Transformer Site Tests
Content
T/P&T..54820.261/76.03.R0
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SEC (CRB) – TRANSMISSION DEPARTMENT
STANDARD PROCEDURE
1
INDEX NUMBER
DATE OF ISSUE
2
3
T/P&T
54820
4a
261/76
4b
5
06
6
R0
28-5-2000
TITEL:
SITE PRE-COMMISSIONING TESTS
FOR POWER TRANSFORMERS
PREPARED:
MUKHTAR FAZAL
CONCURRED BY :
MOHAMMED AL-RAFAA
MANAGER ,PROTECTION & TESTING
APPROVED BY:
HAMAD SAUD ALMOHAIDEB
DIRECTOR, TRANSMISSION
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SEC – CENTRAL REGION BRANCH
TRANSMISSION DEPARTMENT
DISTRIBUTION OF STANDARD PROCEDURE
LOCATION
DATE
VICE PRESIDENT(OPERATIONS SECTOR) OFFICE
DIRECTOR TECHNICAL STUDIES
DIRECTOR PROJECT MANAGEMENT
DIRECTOR GENERATION DEPARTMENT
DIRECTOR GENERATION ENGINEERING DEPT.
DIRECTOR SYSTEM OPERATIONS
DIRECTOR TELECOMMUNICATIONS
DIRECTOR DISTRIBUTION DEPARTMENT
MANAGER O & M AL-QASSIM
MANAGER SUBSTATION MAINTENANCE
MANAGER TRANSMISSION OPERATIONS
MANAGER NETWORK MAINTENANCE
MANAGER PROTECTION AND TESTING
TRANSMISSION REPRESENTATIVE AL-KHARJ
TRANSMISSION REPRESENTATIVE AL-DAWASIR
TRANSMISSION REPRESENTATIVE AL-AFLAG
PROGRAMMING AND RESOURCES DIVISION
TRANSMISSION O&M HAIL
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SITE PRE-COMMISSIONING TESTS FOR POWER TRANSFORMERS
Contents
1.0 GENERAL INFORMATION
1.
TRANSFORMER
2.
TAP CHANGER
2.0 Mechanical checks and visual inspection
3.0 ELECTRICAL TESTS
1.
Insulation tests on auxiliary circuits and control wiring
2.
Core insulation test
3.
Measurement of Insulation Resistance with Polarization Index
and Dissipation Power Factor for main windings insulation.
4.
Ratio test and magnetizing current measurement test
5.
Vector group symbol confirmation test
6.
Winding resistance tests
7.
Calibration of oil and winding temperature gauges
8.
Operation test and current measurements for fans
9.
Fan motors insulation tests and inspection
10. Operation tests for Protection supervisory devices
11. On-load tap changer with motor drive mechanism inspections
12. Test equipment calibration certificates
13. Oil Break Down Voltage test and Dissolved Gas Analysis
4.0
Test Format
5.0 - Load Balancing Check after Energization
1.0 GENERAL INFORMATION
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1.
2.
3.
Before testing collect factory routine and type test reports.
Manufacturers Site test procedure for the particular transformer.
SEC-CRB testing comments during approval stage.
1.1 Transformer Data
From the name plate data collect information about following.
1.
2.
3.
4.
5.
6.
7.
Make.
Type.
Rated current.
Rated voltage.
MVA rating.
Vector group.
Serial no.
1.2 Tap changer data
From the name plate data collect information about following
1. Make.
2. Type.
3. Serial no.
4. No of taps.
5. Motor drive mechanism type.
2.0 MECHANICAL CHECKS AND VISUAL INSPECTION
1. Inspect for physical damage, defects and oil leakage.
2. Check nameplate information correctness and as per contract specifications.
3. Check quality of paint-work and lifting lugs.
4. Check tightness of all bolted connections.
5. Check all grounding are securely connected specially the HV neutral and tank grounds.
6. Check all the valves between tank and radiators are open.
7. Check wheel stoppers.
8. Check the color of silicagel in the breather is blue.
9. Check oil present in temperature sensors pockets.
3.0 ELECTRICAL TESTS
3.1 --Insulation Tests on Auxiliary Circuits and Control Wiring
Perform following tests.
1. Insulation test (By 500v Insulation Tester) for all wiring to ground.
2. Insulation test (By 500v Insulation Tester) for all fan motor and pump motor windings to
ground.
3.2 CORE INSULATION TEST
With 1000v Insulation Tester perform insulation tests as under.
1.
Core lamination to ground.
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2.
3.
Core-clamp to ground.
Core lamination to core-clamp + ground.
14. 3.3 - Measurement of Insulation Resistance with Polarization Index
and Dissipation Power Factor for main windings insulation
3.3.1- Measurement of Insulation Resistance with Polarization Index
Test Diagram
POWER TRANSFORMER
HV WINDINGS
MV WINDINGS
Test leads
INSUL.
TESTER
short
short
GROUND
P RO C E D U R E
Measure insulation resistance(IR) by 5kv Insulation Tester as under.
1.
2.
3.
4.
Record oil/winding temperature and measure IR value as under.
HV TO MV+TERTIARY+GROUND.
MV TO HV+TERTIARY+GROUND.
TERTIARY TO HV + MV+ GROUND.
Note: Normally for new transformers the insulation resistance shall be above 5000
megga ohms
1.
2.
Take reading every minute and upto 10minutes in each case 1,2,3 above.
And estimate polarization indexes (PI) as the ratio of
One minute/ 10minutes megga ohm values
Analyze the results as under.
1. PI less than 1 unsatisfactory.
2. PI between 1.0 to 1.5 doubtful.
3. PI between 1.5 to 2.0 satisfactory
4. PI between 2.0 to 4.0 good.
5. PI more than 4.0 excellent.
Note: Normally PI value above 1.5 is acceptable.
3.3.2 –Measurement of cap. & %Dissipation Power Factor
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Test Diagram
POWER TRANSFORMER
HV WINDINGS
MV WINDINGS
Test leads
short
short
10kv
double
set
GROUND
PROCEDURE
Record the oil/winding temperature.
1. Measure cap. & %Dissipation Power Factor for each winding to ground
capacitance and Dissipation Power Factor measuring equipment.
2.
with
Measure the dissipation factor at 10kv ac applied from the set and calculate the % DF as under.
Power factor = (watts x 100)/(mA x input KV)
Analyze the result as under.
For well dried new power transformer insulation shall have %Dissipation Power Factor value
less than 0.5 % at 20 C .
If the measurements are performed at temperature other than 20 C, then the value shall be corrected
by multiplying with correction factor available in the double set reference data book. . Few CF values are
being tabulated below
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Temp.
correction factor
Temp.
correction factor
(C)
% value
(C)
% value
10
1.38
50
0.28
20
1.0
60
0.17
30
0.63
70
0.12
40
0.42
80
0.09
3.4 - RATIO TEST AND MAGNETIZING CURRENT MEASUREMENT TEST
3.4.1 - By Transformer Turns Ratio Meter (TTR) Method.
Test Diagram
Test leads
test leads
TTR
PROCEDURE
1.
2.
3.
4.
5.
6.
7.
8.
Use TTR test set
Calculate ratio from the name plate data for each tape.
Take care when the vector group is STAR/ DELTA.
Turn ratio = voltage ratio /1.732 in case of star / delta winding group.
Set ratio on dials of TTR.
Refer to TTR catalogue for polarity and dial settings.
Measure deviation in each phase and phase to phase.
Measure exciting current for each phase measured.
ANALYSIS
% Deviation shall not be more than +/-0.5%Error at principal tap.
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Refer to test equipment manufacturers manual for detailed information about the correct use of
that instrument or SEC (CRB) procedure T/T&P..65820.173/34.15.R0.
3.4.2 - BY VOLTAGE METHOD.
Test Diagram.
IR
IY
Vy
3 X 220
IB
V 60HZ
VrSUPPLY
VRN
VYN
VBN
vrn
vyn vbn
PROCEDURE
Connect three phase balanced supply voltage 3X220 V( 60 HZ) on HV side of transformer.
Measure voltage and magnetizing currents in each phase at all taps as under.
1. VRN/Vrn
IR(ma)
2. VYN/Vyn
IY(ma)
3.
VBN/Vbn
IB(ma)
Compare the measured ratio with calculated ratio from nameplate data and calculate % deviation
as
% Deviation = Measured Ratio - Cal Ratio/Cal Ratio X 100 .
ANALYSIS.
% Deviation shall not be more than 0.5 at normal tap.
Magnetizing current should gradually increase in regular steps as the tap changes.
Any abrupt change in the magnetizing current indicates turn to turn short.
Refer to test equipment manufacturers manual for detailed information about the correct use of
that instrument or SEC (CRB) procedure T/T&P..54820.310/105.03.R0.
3.5 - VECTOR GROUP SYMBOL CONFIRMATION TEST.
Following vector groups are available in SEC (CRB) s/s transformers.
Yy0
Yd1
For Main Power Transformers.
For Main Power Transformers.
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DYN11 FOR AUXILIARY TRANSFORMERS
Zyn11 For Auxiliary Earthing Transformers.
1. Vector group is automatically confirmed while testing by TTR.
2. By voltage method various combinations are checked from the actual vector diagram
after measuring the voltages floating upon each other through jumper at one point say at red
phases such as example given below.
EXAMPLE
VECTOR GROUP = Yd1
Rr
conditions to satisfy for verifying Yd1
By = Yy
Yb > Yy
Bb < Yy
ry +yN =RN
b
y
N
B
Y
3.6 - WINDING RESISTANCE TESTS
HV WDG
MV WDG
TRO
1. Use transformer ohm meter (TRO) for test purpose..
2. Record oil & winding temperature.
3. Measure resistance in each tap and on all phases and all windings.
Refer to test equipment manufacturers manual for detailed information about the correct use
of that instrument.
3.7 - CALIBRATION OF OIL AND WINDING TEMPERATURE GAUGES
Following types of oil and winding temperature gauges are installed in SEC (CRB) substations.
1. MESSKO.
2. KIHL-STROMS.
3. TOSHIBA.
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3.7.1 - Thermal Calibration.
Put the sensors in thermal calibrator thermo-well.
Set the temperature on control as under.
1. Set at 40C.
2. Set at 80C.
3. Set at 120C.
4. Set at 160C.
And wait for temperature stability between each set value above for gauge temperature
comparison.
3.7.2 - Thermal Replica by Current Injection.
Check the full load current from nameplate data for the winding under test.
Check the CT ratio for thermal image use.
Calculate the secondary injection current as under.
Injection Current = Full Load Primary Amperes / CTR.
Example.
Full load current = 532 amp
CTR = 532/1.5
532/CTR = 1.2A
3.7.3 - Hot Spot Temperature Rise Calculation.
1. Check in the factory test report for temperature rise test.
2. Take the average value of winding temperature rise above oil at max. rated power or
current.
3. Calculate as under.
Winding Hot spot rise = Av. Winding temp. rise (above oil) x 1.3
Example.
Average winding temp. rise above oil =17.5C
Winding Hot spot rise = 17.5 x 1.3 = 22.75C
1. Take the initial gauge reading before current injection.
2. Inject the specified current say 1.2 amperes.
3. Wait for one hour.
4. Take the final gauge reading and calculate the difference of initial and final readings.
5. Compare with calculated value. If the rise is more or less than calculated rise, then
adjust the resister value according to graph provided.
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Note: Normally it should be 15C to 22C depending on the transformer size and temperature rise
design.
3.7.4 - Temperature Gauges Setting.
For oil temp gauge.
1.
2.
Alarm 1st stage at 85C.
Alarm 2nd stage at 110C.
For Winding temp. Gauge.
1. Fan /pump group one start at 75C.
2. Fan /pump group two start at 85C.
3. Alarm at 110C.
4. TRIP AT 125C.
NOTE: However the temp settings depend upon manufacturers recommendation and
approved by SEC (CRB).
3.8 - OPERATION TEST AND CURRENT MEASUREMENTS FOR FANS
For each fan check and measure following values.
1.
Check motor connection for supply voltage.
2.
3.
Delta connections for 220 volt supply.
Star connection is used for 380-volt supply.
4.
Check fan rotation and air direction.
5. Measure starting current.
6. Measure running current.
7. Measure trip time for MCB by taking one phase out.
8. Check over current alarm initiated.
9. Confirm no bucholze trip during start/stop of pumps.
10. Confirm the correct direction of oil flow during pump operation.
11. Confirm 10-15 seconds delayed operation between two pumps (if provided more than
one pumps)
3.9 - Fan motor insulation tests and inspection
Note down the motor data as under.
9.
10.
11.
12.
13.
14.
15.
Sr no.
Power.
Supply voltage.
Connections delta or star (for delta connection 220v and for star 380v supply).
Insulation class (should be class F).
Speed (rpm).
Rated current.
٣,٩,١ – TESTS ON FAN/PUMP MOTORS
1.
Perform insulation resistance for motor winding with 500volt Insulation Resistance
Tester for one minute.
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2. Motor shaft free to rotate without jamming (in case of fan only).
3. Blades not touching the frame (in case of fan only).
4. Rotation checks in right direction (air flow towards radiators in case of fan and oil flow
towards main tank from radiators in case of pumps).
5. Supply voltage phase sequence check.
Check all motors one by one.
3.10 - Operation tests for Protection Supervisory Devices.
The following types of protection devices are installed on transformers.
3.10.1 - Gas Relays (Bucholze Relays).
To check alarm and trip contacts operation bucholze relays can be tested.
By push button provided.
By gas (dry nitrogen) injection method.
Both methods shall be adopted for test purpose.
3.10.2 - Pressure Relief Vents.
Alarm contacts shall be checked by jumpering the output terminals.
3.10.3 - Pressure Relays.
To be tested by air pressure injection through the valves provided.
3.10.4 - Oil Level Indicator.
During oil filling process the float of this device can be checked for function checks.
Alarm contacts shall be checked by jumpering the output terminals.
3.10.5 - Oil temperature gauges
Fan/pump start/stop, alarm stage 1 and stage2 can be checked by moving the driving shaft of
temperature indicator carefully and confirm the signals are initiated at right settings applied
3.10.6 - Winding temperature gauges
For fan/pump group 1 & fan/pump group 2 the start and stop action, alarm stage 1 and trip
signals initiations can be checked by moving the driving shaft of temperature indicator at
confirm the signals are initiated at right settings applied.
3.10.7 - On Line Dissolved Gas Monitoring Device.
Check alarm stage 1 and 2 through the keyboard provided according to the manufacturer
instructions.
3.10.8 - Oil Leak Detector in the Conservator.
Alarm contacts shall be checked by jumpering the output terminals.
3.10.9 - AC/ DC Supervision Relays
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Alarm Signal initiations are checked by switching of the MCBS or taking out the supply
wires.
3.11 - On-Load Tap Changer with Motor Drive Mechanism Inspections
Check following point on the tap changer panel.
1. The position indicator in motor drive mechanism and tap changer as well as on
AVC/remote control panel showing same tap position
2. Shaft coupling gears lubricated with grease.
3. Check end limits for tap position increase decrease.
4. Check tap change at local and remote position.
5. Check setting of motor protection MCB.
6. No electrical operation while driven by handle.
7. Check tap changer operation.
Manual- local – raise-lower
Auto-local –raise-lower
Indication of tap position for raise and lower action.
Emergency trip and return to normal position on tap upon supply restored.
3.12 - Oil Break down Voltage test and Dissolved Gas Analysis.
Oil samples shall be taken from
1.
2.
3.
4.
Main tank bottom.
Main tank top.
Main conservator.
Tap changer compartment.
At site oil flash test on all a/m samples shall be performed as per IEC 296
with 2.5mm gap.
Average break down value shall not be lower than 50kv ac effective.
For dissolved gas analysis tests sample from main tank bottom shall be taken by the
contractor and send to an independent lab. for analysis purpose.
Another set of samples shall be sent to transmission department oil testing lab. For their
own analysis/comparison purpose.
3.13 - Test Equipment Calibration Certificates
For all test instruments being used by the contractor shall have valid test and calibration
certificates not older than two years from date of issue.
4.0 - Test Formats.
Contractor shall use approved test formats.
No test shall be started until the correct formats are available at site.
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5.0 - Load Balancing Check after Energization
1.
Upon loading the transformer after commissioning, measure the current in each core of
single core cables on 33kv or 13.8kv side of transformer.
2. The current sharing between various cores of same phase shall be nearly equal.
3. Check all the radiators for equal temperature rise and confirm all the radiator valves are in
open position.
14
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SEC (CRB) – TRANSMISSION DEPARTMENT
STANDARD PROCEDURE
1
INDEX NUMBER
DATE OF ISSUE
2
3
T/P&T
54820
4a
261/76
4b
5
06
6
R0
28-5-2000
TITEL:
SITE PRE-COMMISSIONING TESTS
FOR POWER TRANSFORMERS
PREPARED:
MUKHTAR FAZAL
CONCURRED BY :
MOHAMMED AL-RAFAA
MANAGER ,PROTECTION & TESTING
APPROVED BY:
HAMAD SAUD ALMOHAIDEB
DIRECTOR, TRANSMISSION
1
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SEC – CENTRAL REGION BRANCH
TRANSMISSION DEPARTMENT
DISTRIBUTION OF STANDARD PROCEDURE
LOCATION
DATE
VICE PRESIDENT(OPERATIONS SECTOR) OFFICE
DIRECTOR TECHNICAL STUDIES
DIRECTOR PROJECT MANAGEMENT
DIRECTOR GENERATION DEPARTMENT
DIRECTOR GENERATION ENGINEERING DEPT.
DIRECTOR SYSTEM OPERATIONS
DIRECTOR TELECOMMUNICATIONS
DIRECTOR DISTRIBUTION DEPARTMENT
MANAGER O & M AL-QASSIM
MANAGER SUBSTATION MAINTENANCE
MANAGER TRANSMISSION OPERATIONS
MANAGER NETWORK MAINTENANCE
MANAGER PROTECTION AND TESTING
TRANSMISSION REPRESENTATIVE AL-KHARJ
TRANSMISSION REPRESENTATIVE AL-DAWASIR
TRANSMISSION REPRESENTATIVE AL-AFLAG
PROGRAMMING AND RESOURCES DIVISION
TRANSMISSION O&M HAIL
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SITE PRE-COMMISSIONING TESTS FOR POWER TRANSFORMERS
Contents
1.0 GENERAL INFORMATION
1.
TRANSFORMER
2.
TAP CHANGER
2.0 Mechanical checks and visual inspection
3.0 ELECTRICAL TESTS
1.
Insulation tests on auxiliary circuits and control wiring
2.
Core insulation test
3.
Measurement of Insulation Resistance with Polarization Index
and Dissipation Power Factor for main windings insulation.
4.
Ratio test and magnetizing current measurement test
5.
Vector group symbol confirmation test
6.
Winding resistance tests
7.
Calibration of oil and winding temperature gauges
8.
Operation test and current measurements for fans
9.
Fan motors insulation tests and inspection
10. Operation tests for Protection supervisory devices
11. On-load tap changer with motor drive mechanism inspections
12. Test equipment calibration certificates
13. Oil Break Down Voltage test and Dissolved Gas Analysis
4.0
Test Format
5.0 - Load Balancing Check after Energization
1.0 GENERAL INFORMATION
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1.
2.
3.
Before testing collect factory routine and type test reports.
Manufacturers Site test procedure for the particular transformer.
SEC-CRB testing comments during approval stage.
1.1 Transformer Data
From the name plate data collect information about following.
1.
2.
3.
4.
5.
6.
7.
Make.
Type.
Rated current.
Rated voltage.
MVA rating.
Vector group.
Serial no.
1.2 Tap changer data
From the name plate data collect information about following
1. Make.
2. Type.
3. Serial no.
4. No of taps.
5. Motor drive mechanism type.
2.0 MECHANICAL CHECKS AND VISUAL INSPECTION
1. Inspect for physical damage, defects and oil leakage.
2. Check nameplate information correctness and as per contract specifications.
3. Check quality of paint-work and lifting lugs.
4. Check tightness of all bolted connections.
5. Check all grounding are securely connected specially the HV neutral and tank grounds.
6. Check all the valves between tank and radiators are open.
7. Check wheel stoppers.
8. Check the color of silicagel in the breather is blue.
9. Check oil present in temperature sensors pockets.
3.0 ELECTRICAL TESTS
3.1 --Insulation Tests on Auxiliary Circuits and Control Wiring
Perform following tests.
1. Insulation test (By 500v Insulation Tester) for all wiring to ground.
2. Insulation test (By 500v Insulation Tester) for all fan motor and pump motor windings to
ground.
3.2 CORE INSULATION TEST
With 1000v Insulation Tester perform insulation tests as under.
1.
Core lamination to ground.
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2.
3.
Core-clamp to ground.
Core lamination to core-clamp + ground.
14. 3.3 - Measurement of Insulation Resistance with Polarization Index
and Dissipation Power Factor for main windings insulation
3.3.1- Measurement of Insulation Resistance with Polarization Index
Test Diagram
POWER TRANSFORMER
HV WINDINGS
MV WINDINGS
Test leads
INSUL.
TESTER
short
short
GROUND
P RO C E D U R E
Measure insulation resistance(IR) by 5kv Insulation Tester as under.
1.
2.
3.
4.
Record oil/winding temperature and measure IR value as under.
HV TO MV+TERTIARY+GROUND.
MV TO HV+TERTIARY+GROUND.
TERTIARY TO HV + MV+ GROUND.
Note: Normally for new transformers the insulation resistance shall be above 5000
megga ohms
1.
2.
Take reading every minute and upto 10minutes in each case 1,2,3 above.
And estimate polarization indexes (PI) as the ratio of
One minute/ 10minutes megga ohm values
Analyze the results as under.
1. PI less than 1 unsatisfactory.
2. PI between 1.0 to 1.5 doubtful.
3. PI between 1.5 to 2.0 satisfactory
4. PI between 2.0 to 4.0 good.
5. PI more than 4.0 excellent.
Note: Normally PI value above 1.5 is acceptable.
3.3.2 –Measurement of cap. & %Dissipation Power Factor
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Test Diagram
POWER TRANSFORMER
HV WINDINGS
MV WINDINGS
Test leads
short
short
10kv
double
set
GROUND
PROCEDURE
Record the oil/winding temperature.
1. Measure cap. & %Dissipation Power Factor for each winding to ground
capacitance and Dissipation Power Factor measuring equipment.
2.
with
Measure the dissipation factor at 10kv ac applied from the set and calculate the % DF as under.
Power factor = (watts x 100)/(mA x input KV)
Analyze the result as under.
For well dried new power transformer insulation shall have %Dissipation Power Factor value
less than 0.5 % at 20 C .
If the measurements are performed at temperature other than 20 C, then the value shall be corrected
by multiplying with correction factor available in the double set reference data book. . Few CF values are
being tabulated below
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Temp.
correction factor
Temp.
correction factor
(C)
% value
(C)
% value
10
1.38
50
0.28
20
1.0
60
0.17
30
0.63
70
0.12
40
0.42
80
0.09
3.4 - RATIO TEST AND MAGNETIZING CURRENT MEASUREMENT TEST
3.4.1 - By Transformer Turns Ratio Meter (TTR) Method.
Test Diagram
Test leads
test leads
TTR
PROCEDURE
1.
2.
3.
4.
5.
6.
7.
8.
Use TTR test set
Calculate ratio from the name plate data for each tape.
Take care when the vector group is STAR/ DELTA.
Turn ratio = voltage ratio /1.732 in case of star / delta winding group.
Set ratio on dials of TTR.
Refer to TTR catalogue for polarity and dial settings.
Measure deviation in each phase and phase to phase.
Measure exciting current for each phase measured.
ANALYSIS
% Deviation shall not be more than +/-0.5%Error at principal tap.
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Refer to test equipment manufacturers manual for detailed information about the correct use of
that instrument or SEC (CRB) procedure T/T&P..65820.173/34.15.R0.
3.4.2 - BY VOLTAGE METHOD.
Test Diagram.
IR
IY
Vy
3 X 220
IB
V 60HZ
VrSUPPLY
VRN
VYN
VBN
vrn
vyn vbn
PROCEDURE
Connect three phase balanced supply voltage 3X220 V( 60 HZ) on HV side of transformer.
Measure voltage and magnetizing currents in each phase at all taps as under.
1. VRN/Vrn
IR(ma)
2. VYN/Vyn
IY(ma)
3.
VBN/Vbn
IB(ma)
Compare the measured ratio with calculated ratio from nameplate data and calculate % deviation
as
% Deviation = Measured Ratio - Cal Ratio/Cal Ratio X 100 .
ANALYSIS.
% Deviation shall not be more than 0.5 at normal tap.
Magnetizing current should gradually increase in regular steps as the tap changes.
Any abrupt change in the magnetizing current indicates turn to turn short.
Refer to test equipment manufacturers manual for detailed information about the correct use of
that instrument or SEC (CRB) procedure T/T&P..54820.310/105.03.R0.
3.5 - VECTOR GROUP SYMBOL CONFIRMATION TEST.
Following vector groups are available in SEC (CRB) s/s transformers.
Yy0
Yd1
For Main Power Transformers.
For Main Power Transformers.
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DYN11 FOR AUXILIARY TRANSFORMERS
Zyn11 For Auxiliary Earthing Transformers.
1. Vector group is automatically confirmed while testing by TTR.
2. By voltage method various combinations are checked from the actual vector diagram
after measuring the voltages floating upon each other through jumper at one point say at red
phases such as example given below.
EXAMPLE
VECTOR GROUP = Yd1
Rr
conditions to satisfy for verifying Yd1
By = Yy
Yb > Yy
Bb < Yy
ry +yN =RN
b
y
N
B
Y
3.6 - WINDING RESISTANCE TESTS
HV WDG
MV WDG
TRO
1. Use transformer ohm meter (TRO) for test purpose..
2. Record oil & winding temperature.
3. Measure resistance in each tap and on all phases and all windings.
Refer to test equipment manufacturers manual for detailed information about the correct use
of that instrument.
3.7 - CALIBRATION OF OIL AND WINDING TEMPERATURE GAUGES
Following types of oil and winding temperature gauges are installed in SEC (CRB) substations.
1. MESSKO.
2. KIHL-STROMS.
3. TOSHIBA.
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3.7.1 - Thermal Calibration.
Put the sensors in thermal calibrator thermo-well.
Set the temperature on control as under.
1. Set at 40C.
2. Set at 80C.
3. Set at 120C.
4. Set at 160C.
And wait for temperature stability between each set value above for gauge temperature
comparison.
3.7.2 - Thermal Replica by Current Injection.
Check the full load current from nameplate data for the winding under test.
Check the CT ratio for thermal image use.
Calculate the secondary injection current as under.
Injection Current = Full Load Primary Amperes / CTR.
Example.
Full load current = 532 amp
CTR = 532/1.5
532/CTR = 1.2A
3.7.3 - Hot Spot Temperature Rise Calculation.
1. Check in the factory test report for temperature rise test.
2. Take the average value of winding temperature rise above oil at max. rated power or
current.
3. Calculate as under.
Winding Hot spot rise = Av. Winding temp. rise (above oil) x 1.3
Example.
Average winding temp. rise above oil =17.5C
Winding Hot spot rise = 17.5 x 1.3 = 22.75C
1. Take the initial gauge reading before current injection.
2. Inject the specified current say 1.2 amperes.
3. Wait for one hour.
4. Take the final gauge reading and calculate the difference of initial and final readings.
5. Compare with calculated value. If the rise is more or less than calculated rise, then
adjust the resister value according to graph provided.
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Note: Normally it should be 15C to 22C depending on the transformer size and temperature rise
design.
3.7.4 - Temperature Gauges Setting.
For oil temp gauge.
1.
2.
Alarm 1st stage at 85C.
Alarm 2nd stage at 110C.
For Winding temp. Gauge.
1. Fan /pump group one start at 75C.
2. Fan /pump group two start at 85C.
3. Alarm at 110C.
4. TRIP AT 125C.
NOTE: However the temp settings depend upon manufacturers recommendation and
approved by SEC (CRB).
3.8 - OPERATION TEST AND CURRENT MEASUREMENTS FOR FANS
For each fan check and measure following values.
1.
Check motor connection for supply voltage.
2.
3.
Delta connections for 220 volt supply.
Star connection is used for 380-volt supply.
4.
Check fan rotation and air direction.
5. Measure starting current.
6. Measure running current.
7. Measure trip time for MCB by taking one phase out.
8. Check over current alarm initiated.
9. Confirm no bucholze trip during start/stop of pumps.
10. Confirm the correct direction of oil flow during pump operation.
11. Confirm 10-15 seconds delayed operation between two pumps (if provided more than
one pumps)
3.9 - Fan motor insulation tests and inspection
Note down the motor data as under.
9.
10.
11.
12.
13.
14.
15.
Sr no.
Power.
Supply voltage.
Connections delta or star (for delta connection 220v and for star 380v supply).
Insulation class (should be class F).
Speed (rpm).
Rated current.
٣,٩,١ – TESTS ON FAN/PUMP MOTORS
1.
Perform insulation resistance for motor winding with 500volt Insulation Resistance
Tester for one minute.
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2. Motor shaft free to rotate without jamming (in case of fan only).
3. Blades not touching the frame (in case of fan only).
4. Rotation checks in right direction (air flow towards radiators in case of fan and oil flow
towards main tank from radiators in case of pumps).
5. Supply voltage phase sequence check.
Check all motors one by one.
3.10 - Operation tests for Protection Supervisory Devices.
The following types of protection devices are installed on transformers.
3.10.1 - Gas Relays (Bucholze Relays).
To check alarm and trip contacts operation bucholze relays can be tested.
By push button provided.
By gas (dry nitrogen) injection method.
Both methods shall be adopted for test purpose.
3.10.2 - Pressure Relief Vents.
Alarm contacts shall be checked by jumpering the output terminals.
3.10.3 - Pressure Relays.
To be tested by air pressure injection through the valves provided.
3.10.4 - Oil Level Indicator.
During oil filling process the float of this device can be checked for function checks.
Alarm contacts shall be checked by jumpering the output terminals.
3.10.5 - Oil temperature gauges
Fan/pump start/stop, alarm stage 1 and stage2 can be checked by moving the driving shaft of
temperature indicator carefully and confirm the signals are initiated at right settings applied
3.10.6 - Winding temperature gauges
For fan/pump group 1 & fan/pump group 2 the start and stop action, alarm stage 1 and trip
signals initiations can be checked by moving the driving shaft of temperature indicator at
confirm the signals are initiated at right settings applied.
3.10.7 - On Line Dissolved Gas Monitoring Device.
Check alarm stage 1 and 2 through the keyboard provided according to the manufacturer
instructions.
3.10.8 - Oil Leak Detector in the Conservator.
Alarm contacts shall be checked by jumpering the output terminals.
3.10.9 - AC/ DC Supervision Relays
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Alarm Signal initiations are checked by switching of the MCBS or taking out the supply
wires.
3.11 - On-Load Tap Changer with Motor Drive Mechanism Inspections
Check following point on the tap changer panel.
1. The position indicator in motor drive mechanism and tap changer as well as on
AVC/remote control panel showing same tap position
2. Shaft coupling gears lubricated with grease.
3. Check end limits for tap position increase decrease.
4. Check tap change at local and remote position.
5. Check setting of motor protection MCB.
6. No electrical operation while driven by handle.
7. Check tap changer operation.
Manual- local – raise-lower
Auto-local –raise-lower
Indication of tap position for raise and lower action.
Emergency trip and return to normal position on tap upon supply restored.
3.12 - Oil Break down Voltage test and Dissolved Gas Analysis.
Oil samples shall be taken from
1.
2.
3.
4.
Main tank bottom.
Main tank top.
Main conservator.
Tap changer compartment.
At site oil flash test on all a/m samples shall be performed as per IEC 296
with 2.5mm gap.
Average break down value shall not be lower than 50kv ac effective.
For dissolved gas analysis tests sample from main tank bottom shall be taken by the
contractor and send to an independent lab. for analysis purpose.
Another set of samples shall be sent to transmission department oil testing lab. For their
own analysis/comparison purpose.
3.13 - Test Equipment Calibration Certificates
For all test instruments being used by the contractor shall have valid test and calibration
certificates not older than two years from date of issue.
4.0 - Test Formats.
Contractor shall use approved test formats.
No test shall be started until the correct formats are available at site.
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5.0 - Load Balancing Check after Energization
1.
Upon loading the transformer after commissioning, measure the current in each core of
single core cables on 33kv or 13.8kv side of transformer.
2. The current sharing between various cores of same phase shall be nearly equal.
3. Check all the radiators for equal temperature rise and confirm all the radiator valves are in
open position.
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