1. NTPC Tamilnadu Energy Company Ltd
Velammal
Engineering
College
Report on Training
underwent at Vallur
Thermal Power Project
29-06-2015 to 12-07-2015
Er.R.S.RAJPRASAD

2. ACKOWLEDGEMENT
I express my sincere thanks to NTPC TamilNadu Energy
Company Ltd for offering me this opportunity to be trained at
Vallur Thermal Power station, Chennai.
I express my profound sense of gratitude to
Shri.Rajendran, Deputy Manager(Electrical Maintainance),
NTPC for his valuable guidance during the course of the
training programme.
I take this opportunity to thank all the Engineers ,
Supervisors and other workers on site for their support during
the course of this training programme.

3. ABSTRACT
This report inculcates the quantum of knowledge
grasped as a part of the training programme that was offered
at the Vallur Thermal Power Project.
Based on the experience imbibed by virtue of understanding
the nuances of Practical applications, the observations carried
out are briefed out in this report.
The Entire course of training can be
sectionalized into following…
- Testing of Switchgear Relays
- Battery Capacitance Test
- Testing of Transformers
- Stability Test for H.T motor Relays
- Study of the Plant profile

4. TESTING OF SWITCHGEAR RELAYS
Switchgear devices are situated at the key points of electrical
energy transmission and distribution systems.
Their reliability has a decisive influence on the availability,
safety and economic efficiency of electricity supply systems.
Only regular, on-site tests can ensure that switchgear devices
function perfectly throughout their operational life.
The CMC 256plus is the first choice for applications requiring
very high accuracy. This unit is not only an excellent test set
for protection devices of all kinds but also a universal
calibrator.
Its high precision allows the calibration of a wide range of
measuring devices.
Its unique accuracy and flexibility make the CMC 256plus
ideal for protection and measurement equipment
manufacturers for research and development, production and
type testing.

5. The Various tests carried out on the Swithgear relay using
CMC 256 Plus are as follows :
- Overcurrent Protection Test
- Differential Protection Test
- Earth Fault Protection Test
OVERCURRENT PROTECTION TEST:
To evaluate the feasibility for overcurrent
protection offered by the Relay, the pick up value for the
relay is set and corresponding current above the pick up
value is injected into the C.T input of the relay.
If the Relay triggers the trip signal
depending on the time setting (instantaneous or definite
time), then the relay is said to reliable in its operation.
DIFFERENTIAL PROTECTION TEST:
In Differential protection test, the currents
corresponding to the inputs from the two C.T’s are injected
into the relay and is checked .If the relay reacts to the
differential current and executes the corresponding logic
depending upon the magnitude of the differential current,

6. then the relay is considered to be fit for differential
protection.
EARTH FAULT PROTECTION TEST:
A low level arcing ground fault can destroy
switchgear in seconds, before the main service overcurrent
protection will operate. A 480/277 volt solidly grounded
system has sufficient voltage to maintain an arc between one
phase and a ground but not enough current to cause a large
main breaker or fuse to clear the fault quickly. The resulting
arc is similar to an electric weld, consuming large amounts of
metal in the seconds it takes the breaker or fuse to operate. A
properly installed and operating ground fault protection
system will detect and clear the fault in milliseconds, fast
enough to limit damage to acceptable levels.
Using CMC 256 plus, an earth fault is simulated
and checked if the relay reacts effectively to it, within the
ensured response time.
These are the major tests associated
with the testing of Switchgear relays.

7. BATTERY CAPACITANCE TEST
The Battery capacitance test is an important test,
that has to be carried out regularily , so as to ensure the
healthiness of the battery banks and assure reliable support
in case of crisis.
The Various steps involved in the Battery
charging test are as follows :
 Initially check the charging unit if it is in proper
condition to charge the battery unit after it is
discharged. For this, boost the battery from the charger
unit and check.
 Now, isolate the load side from the DCDB (DC
distribution board) .
 Connect a resistive load bank to the rectifier output
terminals of the charging unit, after proper isolation of
the previous load terminals.

8.  Now, close the load isolator switch in the DCDB and add
the load from the resistive load bank.
 After discharging the entire battery bank, check for the
electrolyte parameters, clean if needed and carry out
other maintenance work if required.
 Now remove the Resistive load and start boost charging
the battery bank from the charger unit.
Thus the battery capacitance test is carried out to
ensure the healthiness and reliability of the battery bank so
that it is assured to be available whenever it is needed.

9. TESTING OF TRANSFORMERS
For confirming the specifications and performances
of an Electrical power transformer, it has to go through
numbers of testing procedures. Some tests are done at
manufacturer premises before delivering the transformer. In
addition to that some transformer tests are also carried out at
the consumer site before commissioning and also periodically
in regular & emergency basis throughout its service life.
During the course , UNIT II was shut down and all the
associated auxiliaries were taken for annual maintainance.
So, the tests carried out on the Generator Transformers (G.T)
are listed below.
The various tests carried out on site on the
single phase Generation Transformers are as follows :
Insulation Resistance Test
Magnetizing Current Test
Short Circuit Test
Turns Ratio Test
Winding Resistance Test
Tan-delta Test

10. Test 1 : INSULATION RESISTANCE TEST:
Basically, the Insulation Resistance test is
carried out to verify the insulation levels of the windings of
the transformer as insulation is the most important factor
that determines the substantial quality of operation of an
electrical component.
Testing Apparatus: HV Digital Megger
 The applied voltage from the megger is 5KV
 The resultant IR value obtained will be in GΩ and is
measured at 60 seconds.
 The test point terminals between which the IR value is
measured are
- HV to Ground
- LV to Ground
- HV to LV

11. Test 2 : MAGNETIZING CURRENT TEST:
The Magnetizing current test is carried out , so as to
measure the approximate magnetizing currents flowing
through the winding.
NOTE: As it is practically impossible to determine the exact
magnetizing currents flowing in HV winding, a low voltage
is injected and checked.
z
t
 Apart from the winding to be tested, the other terminal
is kept open .
 On the winding to be tested, inject voltage on the
terminals and measure the current flowing through the
winding using clamp meter
 The injected voltage is 242.7 V
Transformer
SUPPLY
MEASURING NODE

12. Test 3 : SHORT CIRCUIT TEST:
The Short circuit Test is another important test to be
carried out in a transformer, to assess the magnitude of
current flowing in the HV side due to any short circuit faults
in the LV side.
z
t
 Initially the LV side is shorted using shorting cable
 Now, voltage of 246.8 (approx) is injected on the HV
terminals
 The corresponding current flowing through the HV and
LV windings are measured
 The value measured in LV side would be in mA, while the
value measured in HV side would be in A .
Transformer
LV
HV
SUPPLY

13. Test 4 : TURNS RATIO TEST:
The turns ratio test is carried out to analyze the
actual ratio of turns within the transformer windings and
the percentage of error associated with it.
Testing Apparatus: MEGGER TTR320
 Connect the cables “CABLE H” and “CABLE X”
 Ground the Kit
 Connect H1 and H2 to the HV side
 Connect X1 and X2 to the LV side
HV LV
H1
H2
X1
X2

14. Diagram selected in kit for test:
Voltage Rating:
HIGH LOW
230.900
21.000
TAPS 7
On entering the data, the following parameters will
automatically be calculated by the kit :
 Actual Ratio
 % Error
 Excitation Current
 Phasor Deviation
K (Turns ratio)=V2/V1= N2/N1=I1/I2
1:1 1:2 2:1 2:2

15. Test 5 : WINDING RESISTANCE TEST:
The winding Resistance Test is carried out to calculate and
analyze the resistance offered by the winding to the flow of
current.
Testing Apparatus: MEGGER TTR320
 The C+ and C- wires are connected at the terminals of
the winding to be tested
 The V+ and V- wires are connected on the path of C+
and C- respectively as shown in figure.
C+
C-
V+
V-

16.  The Injected DC current is 10A
The observations made on the HV and LV windings are
as follows :
HV winding : R=165 mΩ
LV winding : R=880 mΩ
Test 6 : TAN-DELTA TEST:
The Tan-delta test is one of the most important
tests carried out in a transformer. The Tan-delta test is
mainly carried out to determine the capacitance and
dissipation factor of the transformer.
Dissipation factor = IR/IC
Testing Apparatus: OMICRON CPC 100 and CP TD1
 After all the connections are made, the kit is switched
ON.
 There are two modes of testing: - UST mode and GST
mode
 UST- Ungrounded Specimen Test
GST- Grounded Specimen Test
 In UST mode, tests are run between HV-Tandelta point
and HV-LV

17.  In GST mode, tests are run between HV-Ground and
Tandelta point-Ground
 Guard is used whenever accuracy in results are required
 The Injected Voltages are as follows:
-For higher capacitance : 2kV,5kV and 10kV
-For lower capacitance : 300V and 500V
Thus , depending on the dissipation factor, the ageing of
the transformer is determined.

18. STABILITY TEST FOR HT MOTOR RELAY
The Stability test for HT motor Relay is
mainly done to assure the reliability of the Motor protection
Relay towards Internal Faults.
In this test, an internal fault is simulated by
manually charging the winding terminals with a variac
connected to an external source.
Now, it is observed whether the relay
picks up the fault immediately and trips .
Thus, the stability test ensures that the
relay acts in a feasible manner for any kind of internal faults.

19. STUDY OF PLANT PROFILE
Vallur Thermal Power Station is a
power plant located in Athipattu village, Vallur in Thiruvallur
district, North Chennai, India. The power plant is operated by
NTPC Tamil Nadu Energy Company Limited, a joint venture
between NTPC Limited and TANGEDCO and has three units
with 500 MW each.
In January 2014, the units in the power plant achieved a
record generation of 24.09 million units of electricity.[1] The
project adds nearly 24 million units a day to the grid. Tamil
Nadu is the major beneficiary of power generated from this
facility (about 750 MW), while some of it is supplied
to Andhra Pradesh, Karnataka, Kerala, and Puducherry.
The plant will consume 4.62 mt of coal a year. Coal for the
plant will be brought from Orissa through ship to Ennore
Port, from where it will be transported by closed belt
conveyor system.
The boiler systems at the plant consists of single- or two-pass
type, with front/rear/side mill layout, which can have
single/bi-drum arrangement with natural or controlled
circulation. There is constant or sliding pressure operation,
and hot or cold primary air systems. Steam turbine operates at
a speeds of 3,000 rpm. The main steam is at 130–250 bar at
500–540 °C. Steam reheat is at 30–70 and 500–600 °C. The
back pressure is between 20 and 300 mbar.
The plant has six induced draft cooling towers (IDCTs), which
have a capacity of 30,000 m3/h with nine cells of 21 × 14
m each.The IDCTs use seawater, which is drawn from the
intake channel of North Chennai Thermal Power Station, and
fresh water requirement is met from a desalination plant. The
plant has adopted closed cycle re-circulating type cooling
water system for its operations.

20. The coal conveyor system in the plant includes a 4.4-km-long
pipe conveyor with a capacity of 4,000 tonnes/hour, which is
the world's largest pipe conveyor.
The plant requires 13,400 tonnes of coal per day, and 53
percent of the need is met from domestic coalfields and the
remainder through coal imports.
Following is the unit wise capacity of the 1500 MW plant.
Stage Unit Number Installed Capacity (MW)
Stage I 1 500
Stage I 2 500
Stage I 3 500
GAS INSULATED SWITCHYARD :
A Gas Insulated Switchgear substation (GIS substation) uses
Sulfur hexafluoride gas (SF6 Gas) whose dielectric strength is
higher than air, to provide the phase to ground insulation for
the switchgear of an electrical substation. This works where
by the conductors and contacts are insulated by pressurized
SF6 gas meaning clearances required are smaller than that of
AIS substations. The main advantage of the GIS substation is
that this phase to phase spacing can be reduced significantly
resulting in a substation with comparable load capability to
an AIS substation but with a much smaller compound

21. footprint. This is particularly advantageous in an urban
environment where land size is at a premium. It also results in
a smaller visual impact on a landscape as it can result in a
significantly smaller footprint than its AIS counterpart.
The GIS switch gear shall be of modular design offering high
degree of flexibility. Each module shall be complete with SF6
gas circuit breaker, Disconnectors, Maintenance Grounding
switches, fast Earthing switches, voltage transformers,
Current transformers, bus & elbow sections, cable end
enclosures, L.A., local control cubicle and all necessary
components required for safe & reliable operation and
maintenance. All the three phases of the busbars and
associated equipments like breakers, disconnectors,
instrument transformers & earthing switches etc., are to be
encapsulated in a single gas filled metallic enclosure for 66 &
132 kV voltage class and phase wise separate metallic
enclosures for 400 kV class. The bus bars shall be sub-divided
into compartments including the associated bus bar
disconnector. Bus bars are partitioned at each bay with an
objective to isolate Busbar compartment for the purpose of
extension and at the same time avoid damage to adjacent
bays in the event of fault.
In the past, there was also a concern that only the original
manufacturer of an installation would be willing to accept the
risk of offering an expansion to that installation. The concern
was the integrity of the seals at the point where the original
installation and the expansion came together. As a result, a
purchaser who committed to a GIS installation was

22. perpetually tied to the supplier of that installation for any
future expansion needs, and this put the purchaser at the
mercy of that supplier in future expansions. In recent years,
manufacturers have overcome the technical issues of assuring
the reliability of the seals between dissimilar equipment, so
this problem is less significant today.
Thus, the Vallur Thermal Power Project boasts for its
effectively designed Gas insulated switchgear, thereby
proving to be space efficient in design and pioneering in the
art of keeping pace with the growing electrical technology
and trends.

23. CONCLUSION:
In review, this internship has been an excellent and
rewarding experience. I have been able to meet and network
with so many people , which I would carry ahead in the years
to come.
My experience at Vallur Thermal Power Project has been
invaluable. I thoroughly enjoyed my position and learned a
great deal about all the various aspects of a major Generating
utility.
During the course of training, the insight into professional
practices helped me acquire Practical skills and link theory to
practice in the real Power System workspace.
This training was beneficial for me and I’m thankful that I got
experience to learn many things.