STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
LIST OF CONTENTS
1. PLANT DETAILS
2. TESTING OBJECTIVES
3. TESTING PROPOSALS
4. SERVICES REQUIRED
5. SAFETY PRECAUTIONS
6. EMERGENCY PROCEDURES
7. STATE OF THE PLANT
8. COMMISSIONING PROCEDURE
9. COMPLETION CRITERIA
10. APPENDICES
Page 1 of 12
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 2 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
1. PLANT DETAILS:
This Aux. transformer provides LT service supply to switchyard control
room. It takes 11 KV source supply from 11KV Station Switchboard and
extends 415 volts to the switchyard service board.
TECHNICAL DATA:
1. Auxiliary Transformer
Make : Crompton Greaves Ltd
Rating
Voltage
: 11000 / 433 Volts
Vector Group : Dyn11
Current
: 52.5
/ 1333.4 A
No of taps : 5
Cooling
: 1 MVA
: ONAN
Variation of voltage/tap : 2.5 %
% Impedance : 6
Load loss
: 12000 W
2. AC Service Switchboard
Make : Crompton Greaves Ltd
Voltage : 415 V AC 3 Phase 50Hz
Current : 1250 A
Short circuit current : 45 KA for 1 sec.
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 3 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
2. TESTING OBJECTIVE:
2.1 To test and charge the Aux. Transformer
2.2 To charge the LT switchgear(415 V switchyard Service board)
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
3. TESTING PROPOSAL:
3.1 To carry out following electrical tests for Aux. Transformer
i.
Insulation resistance measurement
ii.
Winding resistance measurement at all taps
iii.
Ratio test at all taps
iv.
Magnetic balance test
v.
Magnetising Current measurement
vi.
Vector group test
vii.
Hi-pot test for HT cable
viii.
Differential Stability test
ix.
REF trip test
x.
Bucholtz, OTI, WTI trip tests
3.2 To carry out the following tests for LT Switchboard
i.
Insulation resistance measurement
ii.
Busbar resistance measurement
Page 4 of 12
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
4. SERVICES REQUIRED:
4.1 Calibrated Test Kit
a. 5 KV Hand/Motorised Megger
b. 500 V Megger
c. Digital Multimeter
d. Micro Ohm meter / Kelvin’s Double bridge
e. Clamp-on meter for current measurement
f. Motwane analog multimeter
g. Thermometer
4.2 Hi- pot AC/DC source Kit.
4.3 3 Phase 415 V AC 50 Hz Supply
4.4 1 Phase 230 V AC 50 Hz Supply
4.5 9 V Battery cell for checking the polarity of Neutral CT
Page 5 of 12
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 6 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
5. SAFETY PRECAUTIONS:
5.1 The engineer-in-charge of the testing team will inform each member of
the test as
to exact nature and extent of his contribution and
responsibilities towards tests carried out.
5.2 Only nominated persons will take part in the tests. All others will remain
clear of the area.
5.3 All persons must acquaint themselves with use and location of fire
extinguishers and First-Aid Box.
5.4 Each test will be carried out under the control of test team leader
5.5 A strict and safe method of applying test leads shall be practiced. Bare
wires should not be used in stead proper lugs must be used. All test
connections shall be tightened and rechecked.
5.6 A record of any alterations made during the tests such as shorts or
disconnections shall be made and annexed to the relevant test
procedures.
5.7 Each test will be carefully planned so that there is no mechanical or
electrical damage to the equipment under test.
5.8 Test area will be kept clean ,clearly defined and cardoned off.
5.9 When high voltage test are being made “Danger/Warning” notices shall
be fixed at relevant points to ensure safety and a sanction for test taken.
All isolating points to be manned.
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 7 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
6. EMERGENCY PROCEDURE:
6.1 Shock treatment chart and first-aid box will be made available.
6.2 Emergency telephone numbers for hospital and fire services shall be
prominently displayed.
6.3 A telephone will be available nearby
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 8 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
7. STATE OF THE PLANT:
7.1 Erection of Aux Transformer,415 V AC Distribution board completed.
7.2 Earthing of the Aux Transformer Neutral & Distribution Board completed
7.3 Clearance from erection department for carrying out various tests obtained.
7.4 Area of test is completely isolated from illegal entry of trespassers
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 9 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
8. COMMISSIONING PROCEDURE:
8.1 Aux Transformer is tested as per the standard Checklist
Insulation resistance test has to be carried out for checking the
healthiness of the Insulation. A 5 / 2.5 kV Megger is used for testing the
insulation between Primary terminal and earth. Same test is repeated
between primary and secondary windings.
However, a 500 V Megger is used for testing Insulation between secondary
and earth. If CT has more than one secondary windings, then insulation is
measured between secondary windings also.
Winding resistance measurement is taken using Micro-Ohm Meter across
phase to phase in primary side and phase to neutral in secondary side.
Secondary side value will be direct reading of winding resistance. Primary
side value will be calculated by adding three measurements and divide it by
two. Then the value of each phase will be this factor minus the combined
resistance of other two phases measured.
Ratio Test is the measurement of secondary voltage while applying known
voltage at the primary side and ensuring that the ratio of Primary voltage to
secondary voltage is equal to Turns ratio or Voltage ratio.
Magnetic Balance Test is the measurement of voltage at other terminals
while applying voltage across any two terminals of primary windings. The
summation of voltage across one of the applied terminal and third terminal
and another applied terminal and third terminal will be equal to the applied
voltage itself at the primary side. The same will be reflected in the secondary
side also.
Magnetizing Current Measurement is the measurement of current of each
phase of primary windings when applying three phase 415 V AC supply
across its terminals.
Vector group test is checking the equality and inequality of vector group of
the Transformer i.e. Dyn11. For which, U phases of Primary and secondary
winding will be shorted together and Voltage will be applied across U & V of
Primary terminals and then check that the following conditions are satisfied.
1U-2V=1U-2W ; 1V-2V=1V-2W ; 2U-2N=2V=2N ; 1U-1V=1U-1W=1V-1W ;
1V-2V > 1V-2W
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 10 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
Hi-pot test for HT cable is the measurement of leakage current (in mA)
through the cable while a high voltage of around 80 % of factory test value
i.e. around 17 KV is applied across each cable and earth.
Differential Stability test is the test to check the stability of Transformer
Differential CTs for its balance under normal operation. For this, Short 3
Phases of Secondary windings and Apply a 3 Phase 415 V AC of
415*52.5/(11000*0.06) = 33 A (approx.) across primary terminals and check
that the corresponding secondary current is reflected in the secondary side
and both the currents at secondary side of CTs are balanced in each phase
and hence no differential current in each phase is flown, can be measured
in the control panel.
REF Trip test is done along with Differential stability test and is carried out
as follows.
1. In the above test, The current through neutral is measured
which will be Zero
2. Short CT secondary of any one of the phases (say U
Phase) at secondary side of Transformer.
3. Due to unbalance, there will be a flow of current through
neutral and REF relay senses this current & enables its
trip contact to give a trip command to transformer.
Field Test consists of Testing the operation of Bucholtz relay, WTI and OTI
switches. Their alarm and trip points are tested either by contact simulation
or by actuating the instruments. The set values of Alarm and Trip points are
as mentioned in their Standard Check list.
8.2 AC DB is tested as per its standard check list.
Insulation Resistance Measurement is carried out using a 500 V megger
across each phase of busbar and earth & across two phases of busbars.
These Values must be more than 2 M Ohms.
`
Bus bar resistance Measurement is a measurement of the resistance of
busbars across its end-to-end joints using a Micro-Ohm meter. This
measurement may be called as millivolt drop measurement of Bus Bar.
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 11 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
9. COMPLETION CRITERIA:
ALL MEASUREMENTS TAKEN DURING TESTS HAVE BEEN
RECORDED AND FOUND IN ACCEPTANCE LIMITS. AUX
TRANSFORMER AND 415 V ACDB ARE READY FOR CHARGING.
STATION: NTPC SIMHADRI
BHEL REF NO : PS-DC-186-500NTPC REF NO : SIM/1/TS/1/
Page 12 of 12
PLANT AREA : 400 KV SWITCHYARD
TESTING SCHEDULE : 11/0.433 KV AUX. TRANSFORMER
10. APPENDICES:
DRAWING :
1. O & M MANUAL OF AUX TRANSFORMER (No. TB-DG-186-3160704,REV 00)
2. GA DRAWINGS OF AUX. TRANSFORMER (No. TB-DG-186-3160701,REV 01)
3. GA DRAWINGS OF AC DB (No. TB-DG-186-316-0381,REV 01)
4. WIRING DIAGRAM OF AUX. TRANSFORMER –TJ BOX (No. TB-DG186-316-0709,REV 01)
5. SCHEMATIC DRAWINGS OF AC DB (No. TB-DG-186-316-0382,R01)