SUMMER INTERNSHIP AT PGCIL 400/220KV WARANGAL SUB-STATION

1. INTERNSHIP ON
ERECTION, COMMISSIONING AND PRE-
COMISSIONING OF 500MVA TRANSFORMER
PRESENTED BY
AKINAPELLI RAHUL
161230007
Internship at
400/220KV POWER GRID
WARANGAL-SS
Submitted at
NATIONAL INSTIUTE OF TECHNOLOY DELHI

2. PGCIL
PGCIL –POWERGRID CORPORATION OF INDIA LIMITED
Incorporated on 23 October 1989 under the Companies Act, 1956 with an authorized share capital of Rs. 5,000
Crore.
POWERGRID transmits about 50% of the total power generated in India on its transmission network.
Its transmission network consists of roughly 148,838 circuit kilometres and 236 EHVAC and HVDC substations,
which provide total transformation capacity of 332,163 MVA. POWERGRID's interregional capacity is 75,050 MW.

3. POWER TRANSMISSION
THROUGH GRID SYSTEM

4. SINGLE LINE DIAGRAM
OF POWER GRID

5. DUTIES OF 400/220KV PGCIL WARANGAL-SS
Connects three power
plants with 400KV lines
Khammam
Bhupalpally
Ramagundam
Supplies power to two
cities with 220KV lines
Nagaram
Durshed
Uses ICT’s to step down
voltage from 400KV to
220KV.
One 500MVA
ICT
Two 315MVA
ICT

6. 500MVA INTER CONNECTING TRANSFORMER
AND ITS PARTS
Provided with 3 windings
•Primary winding of 400KV and star type
•Secondary winding of 220KV and star type
•Tertiary winding of 33KV and delta type
Parts of 500MVA ICT
•Main Tank
•Laminated Core
•Windings
•Transformer Oil
•Conservator Tank
•Breather
•Radiator
•Buchholz Relay
•Pressure relief valve
•Tap Changer

7. ERECTION AND UNLOADING TRANSFORMER
Unloading of transformer
Erection process
• External and internal inspection
• Final tightness test with vacuum and pressure.
• Oil filling
• Hot oil circulation using oil filter machine

8. PRE-COMMISSIONING CHECKS
• 1st step is to prepare testing program schedule.
• Next step is pre-commissioning checks
Examples :-
a. Should be from visible defects,
b. All the valves are tightened properly,
c. Oil is filled up to desired level in bushings, main tank, conservator tank and also in
OLTC etc,.
d. All the cables are tightened and etc,.

9. PRE-COMMISSIONING TESTS
SFRA test:
Sweep Frequency Response Analysis is
to evaluate the mechanical integrity of core,
windings and clamping structures by
measuring their electrical transfer functions
over a wide frequency range.
Performed at 10V AC from 20Hz-20MHz
supply
Eg :-
Voltage and Turns ratio measurement:
1. Voltage ratio test uses digital multi
meter performed at 415V.
2. Transformer turns ratio test uses
automatic transformer turns ratio(TTR)
meter performed at 110V.

10. • Performed to locate defect
in magnetic core structure,
shifting of windings, failure
in turn to turn insulation or
problem in tap changer.
• Performed at 440V AC on
HV side and LV side is open
• Carried on min, normal and
max tap positions.
Magnetizing
current test:
• Performed to check balance in the
magnetic circuit.
• 1-phase 230V supplied between phase
and neutral and measure the voltage
induced in other two phases of the
same winding.
• Equipment used is digital multimeter.
• When voltage is applied at R-phase, Y-
phase should be 50-90% and B- phase
should be in 20-40%
• When voltage is applied at Y-phase,
other two phases induced voltage
should be in 30-70%.
Magnetic
balance
test:

11. • Performed to detect winding
movement which occurs due to
heavy fault current or mechanical
damage during transportation.
• A 3 phase 440V supply is given to
HV winding and LV is shorted .
• Measure primary voltage and
current in primary and secondary
• Performed on min, normal and
maximum tap positions.
• Acceptance values should be
within 3 % of impedance specified.
Short
circuit
impedance
test
• BDV test
acceptance value > 70KV
• PPM test
Moisture content < 5ppm
Tan delta at 90 degree
<0.01 Moisture content <
5ppm
Oil
characteristics
test

12. OTHER REMAINING TESTS
Capacitance and tan delta measurement
Verification of vector group and polarity test
Measurement of winding resistance
Winding insulation resistance measurement
Core insulation test
Testing on bushing CT’s
Measurement of earthing resistance

13. FINAL COMMISSIONING CHECKS
All the test results are verified and compared with factory results before commissioning.
No leakage oil in any part of unit. Ensure oil level in the Bushings
Ensure that tertiary winding terminals are insulated, when they are not used.
Ensure earthing of Neutral, main tank body, radiator frame structure, fans and motor.
And all the final verifications, continuity between switchyard and transformer meters, connections, sensors, fans attached and etc,.

14. ENERGISATION OF UNIT
1st charge the transformer under no load for 24 – 48 hours.
Gradually load the transformer observing the noise, vibration, temperature rise, oil leakage etc.
Check OLTC operation.
Carry out Thermo vision scanning of HV/LV terminals and tank body.
Carry out DGA test of oil as per schedule given in flow chart of this manual.

15. THANK YOU!!!