Report of Industrial training at a thermal powerplant

1. SHRI SINGAJI THERMAL POWER PLANT
(SSTPP)
INDUSTRIAL
TRAINING-REPORT
Submitted to
Rajiv Gandhi Proudyogiki Vishwavidyalaya
towards Partial Fulfillment of the Degree of
BACHELOR OF ENGINEERING
(Electrical & Electronics Engineering)
GUIDED BY
Mr. Kamlesh Gupta
SUBMITTED BY
Utkarsh Chaubey
ELECTRICAL & ELECTRONICS
ENGINEERING DEPARTMENT
INSTITUTE OF ENGINEERING & SCIENCE
IPS ACADEMY INDORE
2019-20

2. ELECTRICAL & ELECTRONICS
ENGINEERING DEPARTMENT
INSTITUTE OF ENGINEERING & SCIENCE
IPS ACADEMY INDORE
2019-20
CERTIFICATE
I are pleased to certify that the Industrial Training (EX-705) entitled Industrial training at “Shri Singaji
Thermal Power Plant (SSTPP)” submitted by following student is accepted.
Utkarsh Chaubey Roll No. 0808EX141074
INTERNAL EXAMINER EXTERNAL EXAMINER
Date: Date:

3. INDUSTRIAL-CERTIFICATE

4. A C K N OW L E D G E M E N T
It is our great pleasure to express our profound gratitude to our esteemed guide Mr. Kamlesh
Gupta, Electrical and Electronics Engg. Deptt., IES, IPS Academy Indore for their valuable
inspiration, able guidance and untiring help, which enabled us to carry out and complete this work.
We are grateful to Mr. Manish Sahajwani, Professor & Head-Department of Electrical and
Electronics Engineering IES, IPS Academy Indore, for his keenness towards this work and efforts
put in, and also for sharing his valuable time to our problems and providing useful solutions.
I express our sincere gratitude to Dr. Archana Keerti Chowdhary, Principal, IES, IPS Academy,
Indore for extending all the facilities during the course of study.
At this juncture I also take this opportunity to express our deep gratitude to all the faculties of
Electrical and Electronics Engineering Department, for their appreciation and moral support.
I’m also thankful to all our friends who helped us directly or indirectly to bring the dissertation
work to the present shape.
Date: Name of Student
Utkarsh Chaubey

5. ABSTRACT
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated,
turns into steam and spins a steam turbine which drives an electrical generator. After it passes
through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this
is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to
the different fuel sources. Some prefer to use the term energy centre because such facilities convert
forms of heat energy into electricity. Some thermal power plants also deliver heat energy for
industrial purposes, for district heating, or for desalination of water as well as delivering electrical
power. A large part of human CO2 emissions comes from fossil fueled thermal power plants;
efforts to reduce these outputs are various and widespread. At present 54.09% or 93918.38 MW
(Data Source CEA, as on 31/03/2011) of total electricity production in India is from Coal Based
Thermal Power Station. A coal based thermal power plant converts the chemical energy of the coal
into electrical energy. This is achieved by raising the steam in the boilers, expanding it through the
turbine and coupling the turbines to the generators which converts mechanical energy into electrical
energy.

6. CONTENT

Power Plant Overview 1

Thermal Power Plant 2

Rankine Cycle 3

Classification of Thermal Power Plant 5
1) By Fuel 5
2) By Prime Mover 5

Typical View of a Thermal Power Plant 7

Site Selection 9

Working of SSTPP 12

Generator 15

Switch-Yard 16
1) Bus-Bar 17
2) Lightening Arrester 17
3) SF6 Circuit Breaker 18
4) Isolator 20
5) Current Transformer 21
6) Potential Transformer 22

Power Transformer 23
1) Transformer Oil 24
2) Insulation Resistance Test 27

Protection of Transformer 29
1) Breather 29
2) Radiator 30
3) Conservator Tank 31
4) Buchholz Relay 32

Transformer Noise 33

Safety Measures 34

Conclusion 35

7. 1 | P a g e
POWER PLANT OVERVIEW
Shree Singaji Super Thermal Power Project is a coal-fired power plant located near Dongaliya
village near by Mundi of Khandwa District in Madhya Pradesh state of India. This project is
owned by MPPGCL (Madhya Pradesh Power Generating Company limited). The water required
is taken from Indira Sagar Reservoir on Narmada River. Coal linkage is achieved with South
Eastern Coalfields Limited.
The Project was originally envisaged to be constructed in three development phases, but only
two of the three phases have been approved for construction.
The first phase consists of 2 units with a generation capacity of 600 MW each. First unit was
commissioned in February 2014 and, as of June 2014, the second unit is expected to complete
in October 2014.
The second phase consists of 2 units with generation capacity of 660 MW each. These units
would be super critical thermal plants. As of December 2014, construction of phase two had not
yet started.
Staage
Unit
Number
Installed
Capacity
(MW)
Date of
Commission
ing
Statu
s
First 1 600
2014,
February
Runn
ing
First 2 600
2014,
December
Runn
ing
Second 3 660
2018,
November
Runn
ing
Second 4 660 2019, March
Runn
ing

8. 2 | P a g e
THERMAL POWER PLANT
A thermal power station is a power plant in which the prime mover is steam driven. Water is
heated, turns into steam and spins a stream turbine which drives an electrical generator. After it
passes through the turbine, the steam is condensed in a condenser and recycled to where it was
heated, this is known as rankine cycle.

9. 3 | P a g e
RANKINE CYCLE
The rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into
mechanical work. The heat is supplied externally to a close loop, which usually uses water as the
working fluid.
Process 1-2: The working fluid is pumped from low to high pressure. As the fluid is a liquid at
this stage, the pump requires little input energy.

10. 4 | P a g e
Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an
external heat source to become a dry saturated vapour. The input energy required can be easily
calculated using mollier diagram or h-s chart or enthalpy-entropy chart also known as steam
tables.
Process 3-3’
: Super-heating of steam because compression by the pump and expansion in the
turbine is not isentropic. So as the water condenses, water droplets hit the turbine blades causing
pitting and erosion of the turbine, so by super-heating we make the steam dry.
Process 3’
-4’
: The dry saturated vapour expands through a turbine, generating power. This
decreases the temperature and pressure of the vapour, and some condensation may occur. The
output in this process can be easily calculated using the enthalpy-entropy chart or the steam
tables.
Process 4’
-1: The wet vapour then enters a condenser where it is condensed at a constant
pressure to become a saturated liquid.

11. 5 | P a g e
CLASSIFICATION OF THERMAL POWER PLANTS
Thermal power plants are classified by the type of fuel and the type of prime
mover installed.
1) By Fuel
• Nuclear power plants use nuclear heat to operate a steam turbine generator.
• Fossil fueled power plants may also use a steam turbine generator or in the case
of natural gas fired plants may use a combustion turbine.
• Geothermal power plants use steam extracted from hot underground rocks.
• Renewable energy plants may be fueled by waste from sugar cane, municipal
solid waste, landfill methane, or other forms of biomass.
• In integrated steel mills, blast furnace exhaust gas is a low-cost, although low-
energy-density, fuel.
• Waste heat from industrial processes is occasionally concentrated enough to
use for power generation, usually in a steam boiler and turbine.
• Solar thermal electric plants use sunlight to boil water, which turns the generator.
2) By Prime Mover
• Steam turbine plants use the dynamic pressure generated by expanding steam to
turn the blades of a turbine. Almost all large non-hydro plants use this system.
• Gas turbine plants use the dynamic pressure from flowing gases to directly
operate the turbine. Natural-gas fueled turbine plants can start rapidly and so are
used to supply "peak" energy during periods of high demand, though at higher
cost than base-loaded plants. These may be comparatively small units, and
sometimes completely unmanned, being remotely operated. This type was
pioneered by the UK, Prince town being the world's first, commissioned in 1959.
• Combined cycle plants have both a gas turbine fired by natural gas, and a steam
boiler and steam turbine which use the exhaust gas from the gas turbine to
produce electricity. This greatly increases the overall efficiency of the plant, and
many new base load power plants are combined cycle plants fired by natural gas.

12. 6 | P a g e
• Internal combustion Reciprocating engines are used to provide power for isolated
communities and are frequently used for small cogeneration plants. Hospitals,
office buildings, industrial plants, and other critical facilities also use them to
provide backup power in case of a power outage. These are usually fueled by
diesel oil, heavy oil, natural gas and landfill gas.

13. 7 | P a g e
TYPICAL VIEW OF A COAL FIRED
THERMAL POWER PLANT
1. Cooling tower 2. Cooling water Pump
3. Transmission line (3-phase) 4. Step-up transformer (3-phase)
5. Electrical generator (3-phase) 6. Low pressure steam turbine
7. Condensate pumps 8. Surface condenser
9. Intermediate pressure steam turbine
10. Steam Control valve
11. High pressure steam turbine 12. Deaerator
13. Feed water heater 14. Coal conveyor
15. Coal hopper 16. Coal pulverizer
17. Boiler steam drums 18. Bottom ash hopper
19. Super heater 20. Forced draught (draft) fan
21. Re heater 22. Combustion air intake
23. Economizer 24. Air pre heater
25. Precipitator 26. Induced draught (draft) fan
27. Flue gas stack

14. 8 | P a g e

15. 9 | P a g e
SITE SELECTION OF THERMAL POWER PLANT
In general, both the construction and operation of a power plant requires the
existence of some conditions such as water resources and stable soil type. Still
there are other criteria that although not required for the power plant, yet should
be considered because they will be affected by either the construction or
operation of the plants such as population centers and protected areas. The
following list corresponds most of the factors that was studied and considered in
selection of proper site for Dongalia power plant construction:
• Transportation Network: Easy and enough access to transportation network is
required in both power plant construction and operation periods.
• Power Transmission Network: To transfer the generated electricity to the
consumers, the plant should be connected to electrical transmission system.
Therefore the nearness to the electric network can play a roll.
• Geology and Soil Type: The power plant should be built in an area with soil and
rock layers that could stand the weight and vibrations of the power plant.
• Earthquake and Geological Faults: Even weak and small earthquakes can
damage many parts of a power plant intensively. Therefore the site should be
away enough from the faults and previous earthquake areas.
• Topography: It is proved that high elevation has a negative effect on production
efficiency of gas turbines. In addition, changing of a sloping area into a flat site
for the construction of the power plant needs extra budget. Therefore, the
parameters of elevation and slope should be considered.
• Rivers and Flood-ways: obviously, the power plant should have a reasonable
distance from permanent and seasonal rivers and flood-ways.

16. 10 | P a g e
• Water Resources: For the construction and operating of power plant different
volumes of water are required. This could be supplied from either rivers or
underground water resources. Therefore to meet the requirement of water supply
a 18m high dam is constructed over narmada river.
• Environmental Resources: Operation of a power plant has important impacts on
environment. Therefore, priority will be given to the locations that are far enough
from national parks, wildlife, protected areas, etc.
• Population Centers: For the same reasons as above, the site should have an
enough distance from population centers.
• Need for Power: In general, the site should be near the areas that there is more
need for generation capacity, to decrease the amount of power loss and
transmission expenses.
• Climate: Parameters such as temperature, humidity, wind direction and speed
affect the productivity of a power plant and always should be taken into account.
• Land Cover: Some land cover types such as forests, orchard, agricultural land,
pasture are sensitive to the pollutions caused by a power plant. The effect of the
power plant on such land cover types surrounding it should be counted for.
• Area Size: Before any other consideration, the minimum area size required for
the construction of power plant should be defined.
• Distance from Airports: Usually, a power plant has high towers and chimneys
and large volumes of gas. Consequently for security reasons, they should be away
from airports.

17. 11 | P a g e
• Archaeological and Historical sites: Usually historical building are fragile and
at same time very valuable. Therefore the vibration caused by power plant can
damage them, and a defined distance should be considered.

18. 12 | P a g e
WORKING OF SHRI SINGAJI THERMAL
POWER PLANT
1) Coal is conveyed with the help of trucks from the nearby captive coal mines
to the coal handling plant.
2) In coal handling plant (CHP) coal is separated as high grade coal and low
grade coal. High grade coal is conveyed to JPL and low grade coal is
conveyed to SSTPP. Pulverization of coal is also takes place in CHP.
3) From CHP coal is transported to boiler there it is mixed with preheated air
driven by the Forced draught fan.
4) The hot air-fuel mixture is forced at high pressure into the Boiler where it
rapidly ignites.
5) Water of a high purity flows vertically up the tube-lined walls of the boiler,
where it turns into steam, and is passed to the boiler drum, where steam is
separated from any remaining water.
6) Water is supplied from DE-mineralized plant (DM) plant.
7) The steam passes through a manifold in the roof of the drum into the pendant
Super heater where its temperature and pressure increase rapidly to around
136 bar and 535°C, sufficient to make the tube walls glow a dull red.
8) The steam is piped to the high-pressure turbine, the first of a three-stage
turbine process.
9) A Steam governor valve allows for both manual control of the turbine and
automatic set point following.
10) The steam is exhausted from the high-pressure turbine, and reduced in both
pressure and temperature, is returned to the boiler re-heater.
11) The reheated steam is then passed to the Intermediate pressure turbine, and
from there passed directly to the low pressure turbine set.
12) The exiting steam, now a little above its boiling point, is brought into thermal
contact with cold water (pumped in from the cooling tower) in the Condenser,
where it condenses rapidly back into water, creating near vacuum-like
conditions inside the condenser chest.

19. 13 | P a g e
13) The condensed water is then passed by a feed pump through a deaerator
(device that is widely used for the removal of oxygen and other dissolved
gases from the feed water to steam-generating boilers) and pre-warmed, first
in a feed heater powered by steam drawn from the high pressure set, and then
in the Economizer, before being returned to the boiler drum.
14) The cooling water from the condenser is sprayed inside a Cooling tower,
creating a highly visible plume of water vapor, before being pumped back to
the Condenser in cooling water cycle.
15) The three turbine sets are coupled on the same shaft as the three-phase
electrical Generator of 135 MW which generates an intermediate level
voltage (typically 13-15 kV).
16) This is stepped up by the generating transformer of 180 MVA to a voltage
more suitable for transmission (typically 220-250 kV) and is sent out onto the
three-phase transmission system.
17) Exhaust gas from the boiler is drawn by the induced draft fan through an
Electrostatic Precipitator (ESP) and is then vented through the Chimney stack.
18) ESP is a device which removes dust or other finely divided particles from flue
gases by charging the particles inductively with an electric field, then
attracting them to highly charged collector plates also known as precipitator.
The process depends on two steps. In the first step the suspension passes
through an electric discharge area where ionization of the gas occurs. The
charged particles drift toward an electrode of opposite sign and are deposited
on the electrode where their electric charge is neutralized. Among the
advantages of the ESP is its ability to handle large volumes of gases, at
elevated temperatures if necessary, with a reasonably small pressure drop, and
the removal of particles in the micrometer range.
19) Fly ash is captured and removed from the flue gas by ESP located at the
outlet of the furnace and before the induced draft fan. The fly ash is
periodically removed from the collection hoppers below the precipitators.
Generally, the fly ash is pneumatically transported to storage silos for
subsequent transport by trucks.
20) Flue gases coming out of the boiler carry lot of heat. Function of economizer
is to recover some of the heat from the heat carried away in the flue gases up
the chimney and utilize for heating the feed water to the boiler. It is placed in
the passage of flue gases in between the exit from the boiler and the entry to
the chimney. The use of economizer results in saving in coal consumption,

20. 14 | P a g e
increase in steaming rate and high boiler efficiency but needs extra
investment and increase in maintenance costs and floor area required for the
plant.
21) The remaining heat of flue gases is utilized by air preheater. It is a device
used in steam boilers to transfer heat from the flue gases to the combustion air
before the air enters the furnace. Also known as air heater; air-heating system.
It is kept at a place nearby where the air enters in to the boiler. The purpose of
the air pre-heater is to recover the heat from the flue gas from the boiler to
improve boiler efficiency by burning warm air which increases combustion
efficiency, and reducing useful heat lost from the flue. After extracting heat
flue gases are passed to ESP.

21. 15 | P a g e
GENERATOR
In SSTPP, there are four synchronous generators of rating 600 MW are used. It is
a 3-phase, two pole synchronous generator. It also has brush-less excitation
system. Its rated current is 7060 A and rated power factor is 0.8 lagging. Its
efficiency is about 98.65% at full load. Its r.p.m. is 3000. Generators are used to
convert mechanical energy to electrical energy. It works on the principle of
Faraday’s law of induction. It contains a stationary stator and a spinning rotor.
Each generator is mechanically coupled with turbine through a shaft. Shaft is
further connected to a coil of a copper wire known as armature. On either side of
the armature, on the casing of the generator, we have two polar field magnets that
create a magnetic field inside the space within the generator. As the rotor, shaft
and armature rotates, they move within the magnetic field created by the magnets.

22. 16 | P a g e
SWITCH-YARD
Switch-yard forms an integral part of any power plant. Switch-Yard provides the
facility of switching, control and protection of electric power. Here voltage is
transformed from low (13.6 KV) to high (220 KV). In SSTPP switch-yard there
are total 16 bays. All switch-yard Equipments are grounded by two earthing
connections.
It consists of following Equipments:
 BUS-BAR
 LIGHTENING ARRESTER
 SF6 CIRCUIT BREAKER
 ISOLATOR
 CURRENT TRANSFORMER
 POWER TRANSFORMER
 POTENTIAL TRANSFORMER
A VIEW OF switch-yard

23. 17 | P a g e
1. BUS-BAR
In electrical power distribution, a bus-bar is a strip or bar of copper, brass or aluminum
that conducts electricity within a switchboard, distribution board, substation, battery
bank or other electrical apparatus. Its main purpose is to conduct a substantial current of
electricity.
The cross-sectional size of the bus-bar determines the maximum amount of current that
can be safely carried. Bus-bar can have a cross-sectional area of as little as 10 mm2
but
electrical substations may use metal pipes of 50 mm in diameter (20 cm2
) or more as
BUS-BARs.
2. LIGHTENING ARRESTER
A surge arrester is a product installed near the end of any conductor which is long
enough before the conductor lands on its intended electrical component. The purpose is
to divert damaging lightning-induced transients safely to ground. This equipment is
always placed before the costliest equipments to provide better safety.
When an electrically charged cloud comes nearby an electrical transmission line, the
cloud induces an electric charge in the line. When the charge cloud is suddenly
discharged through lightening the induced charge is no longer static. It starts travelling
and originate dynamic transient over voltage. The transient over voltage travel towards
both load and source side on transmission line because of distributed line inductance and
stray capacitance. This surge voltage travels with speed of light. At the end of

24. 18 | P a g e
transmission line as the surge impedance changes surge voltage wave reflected back.
This forward and backward travelling of surge voltage wave continues until the energy of
impulse is attenuated by line resistance. This causes stress on transmission line. So, to
prevent equipments we use lightening arrester.
3. SF6 CIRCUIT BREAKER
A circuit breaker is an automatically operated electrical switch designed to protect an
electrical circuit from damage caused by overload or short circuit. Its basic function is to
detect a fault condition and interrupt current flow. A circuit breaker, in which the current
carrying contacts operate in SF6 gas.
SF6 has excellent insulating property and has high electronegativity that means it has
high affinity of absorbing free electron whenever a free electron collides with SF6 gas
molecule it is absorbed by that gas molecule and forms a negative ion.
SF6 + e-
SF6
-
SF6 + e-
SF5
-
+ F
These negative ion obviously much heavier than free e-
and therefore over all mobility of
the charged particle in the SF6 gas is much less as compared to other gas. We know that
mobility of charged particle is majorly responsible for conducting current through a gas.

25. 19 | P a g e
Hence, for heavier and less mobile charged particle in SF6 gas, it acquires very high
dielectric strength. Gas also has very good heat transfer property due to its low gaseous
viscosity.
Working of SF6 Circuit Breaker
The working of SF6 CB of first generation was quite simple it is some extent similar to
air blast circuit breaker. Here SF6 gas was compressed and stored in high pressure
reservoir. During operation of SF6 circuit breaker this highly compressed gas is
released through the arc in breaker and collected to relatively low pressure reservoir and
then it pumped back to the high pressure reservoir for re utilize.
The working of SF6 circuit breaker is little bit different in modern time. Innovation of
puffer type design makes operation of SF6 CB much easier. In buffer type design, the arc
energy is utilized to develop pressure in the arcing chamber for arc.
Here the breaker is filled with SF6 gas at rated pressure. There are two fixed contact
fitted with a specific contact gap. A sliding cylinder bridges these to fixed contacts. The
cylinder can axially slide upward and downward along the contacts. There is one
stationary piston inside the cylinder which is fixed with other stationary parts of the SF6
circuit breaker, in such a way that it cannot change its position during the movement of
the cylinder. As the piston is fixed and cylinder is movable or sliding, the internal
volume of the cylinder changes when the cylinder slides.

26. 20 | P a g e
During opening of the breaker the cylinder moves downwards against position of the
fixed piston hence the volume inside the cylinder is reduced which produces compressed
SF6 gas inside the cylinder. The cylinder has numbers of side vents which were blocked
by upper fixed contact body during closed position. As the cylinder move further
downwards, these vent openings cross the upper fixed contact, and become unblocked
and then compressed SF6 gas inside the cylinder will come out through this vents in high
speed towards the arc and passes through the axial hole of the both fixed contacts. The
arc is quenched during this flow of SF6 gas.
During closing of the circuit breaker, the sliding cylinder moves upwards and as the
position of piston remains at fixed height, the volume of the cylinder increases which
introduces low pressure inside the cylinder compared to the surrounding. Due to this
pressure difference SF6 gas from surrounding will try to enter in the cylinder. The higher
pressure gas will come through the axial hole of both fixed contact and enters into
cylinder via vent and during this flow; the gas will quench the arc.
4. ISOLATOR
Circuit breaker always trip the circuit but open contacts of breaker cannot be visible
physically from outside of the breaker and that is why it is recommended not to touch
any electrical circuit just by switching off the circuit breaker. So for better safety there
must be some arrangement so that one can see open condition of the section of the circuit
before touching it. Isolator is a mechanical switch which isolates a part of circuit from
system as when required. Electrical isolators separate a part of the system from rest for
safe maintenance works.
So definition of isolator can be rewritten as Isolator is a manually operated mechanical
switch which separates a part of the electrical power system normally at off load
condition.
Operation
As no arc quenching technique is provided in isolator it must be operated when there is
no chance current flowing through the circuit. No live circuit should be closed or open by
isolator operation. A complete live closed circuit must not be opened by isolator
operation and also a live circuit must not be closed and completed by isolator operation
to avoid huge arcing in between isolator contacts. That is why isolators must be open
after circuit breaker is open and these must be closed before circuit breaker is closed.
Isolator can be operated by hand locally as well as by motorized mechanism from remote
position. Motorized operation arrangement costs more compared to hand operation;
hence decision must be taken before choosing an isolator for system whether hand

27. 21 | P a g e
operated or motor operated economically optimum for the system. For voltages up to
145KV system hand operated isolators are used whereas for higher voltage systems like
245 KV or 420 KV and above motorized isolators are used.
5. CURRENT TRANSFORMER
A CT is an instrument transformer in which the secondary current is substantially
proportional to primary current and differs in phase from it by ideally zero degree. It is
used in electrical power system for stepping down currents of the system for metering
and protection purpose. Actually relays and meters used for protection and metering, are
not designed for high currents and voltages. High currents or voltages of electrical power
system cannot be directly fed to relays and meters. CT steps down rated system current
to 1 Amp or 5 Amp. The relays and meters are generally designed for 1 Amp and 5 Amp.
Turns ratio of current transformer is 2000/1.
A CT functions with the same basic working principle of electrical power transformer,
but here is some difference. In an electrical power transformer or other general purpose
transformer, primary current varies with load or secondary current. In case of CT,
primary current is the system current and this primary current or system current
transforms to the CT secondary, hence secondary current depends upon primary current
of the current transformer.

28. 22 | P a g e
6. POTENTIAL TRANSFORMER
Potential transformer or voltage transformer gets used in electrical power system for
stepping down the system voltage to a safe value which can be fed to low ratings meters
and relays. Commercially available relays and meters used for protection and metering,
are designed for low voltage. Primary of this transformer is connected across the phase
and ground. Just like the transformer used for stepping down purpose, potential
transformer i.e. PT has lower turns winding at its secondary. The system voltage is
applied across the terminals of primary winding of that transformer, and then
proportionate secondary voltage appears across the secondary terminals of the PT. The
secondary voltage of the PT is generally 110 V.

29. 23 | P a g e
POWER TRANSFORMER
A transformer is a static machine used for transforming power from one circuit to another
without changing frequency. This is a very basic definition of transformer. Generation of
electrical power in low voltage level is very much cost effective. Hence electrical power
is generated in low voltage level. Theoretically, this low voltage level power can be
transmitted to the receiving end. But if the voltage level of a power is increased, the
electric current of the power is reduced which causes reduction in ohmic or I2
R losses in
the system, reduction in cross sectional area of the conductor i.e. reduction in capital cost
of the system and it also improves the voltage regulation of the system. Because of these,
low level power must be stepped up for efficient electrical power transmission. This is
done by step up transformer at the sending side of the power system network. As this
high voltage power may not be distributed to the consumers directly, this must be
stepped down to the desired level at the receiving end with the help of step down
transformer. These are the uses of electrical power transformer in the electrical power
system.
In SSTPP there are basically 4 different ratings of transformers are used:
1. GENERATING TRANSFORMER (GT)
2. SUBSTATION TRANSFORMER (ST)
3. UNIT AUXILARY TRANSFORMER (UAT)
4. MINES SUBSTATION TRANSFORMER (MST)

30. 24 | P a g e
GENERATING TRANSFORMER:
There are total 4 generating transformer of rating 180 MVA each, which is used to step
up the voltage from 13.6 KV to 220 KV. Windings in GT are star-delta connected.
SUBSTATION TRANSFORMER:
There are total 3 substation transformers of 40 MVA each. This is used when the plant
shut down or any unit shut down takes place. So, to start the plant/unit they take the
power from JPL so to step down the voltage. Windings in ST are star-star connected.
Unit 3 and 4 are connected to a common ST.
UNIT AUXILIARY TRANSFORMERS:
There are total 4 unit auxiliary transformers of 25 MVA each. This is used to run the
auxiliaries of the plant means once with the help of ST unit is started then the generated
power is utilized with the help of UAT. Windings in UAT are delta-star connected.
MINES SUBSTATION TRANSFORMER:
Near SSTPP there is a Dongalia captive coal mines through which coal is supplied to the
plant. To supply power to the mines 2 MST’s are installed in the plant of 50 MVA each.
 TRANSORMER OIL
In SSTPP oil immersed transformers are used. Oil in transformer used is called mineral
oil. Transformer oil serves mainly two purposes one it is liquid insulation in electrical
power transformer and two it dissipates heat of the transformer i.e. acts as coolant. In
addition to these, this oil serves other two purposes, it helps to preserve the core and
winding as these are fully immersed inside oil and another important purpose of this oil
is, it prevents direct contact of atmospheric oxygen with cellulose made paper insulation
of windings, which is susceptible to oxidation.
TESTING OF TRANSFORMER OIL
There are basically 2 tests which are performed generally:
Dissolved gas analysis (DGA) test
Whenever electrical power transformer goes under abnormal thermal and
electrical stresses, certain gases are produced due to decomposition of
transformer insulating oil. Which affect the insulation of windings. when the fault
is major, the production of decomposed gases are more and they get collected in

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Buchholz relay. But when abnormal thermal and electrical stresses are not
significantly high the gasses due to decomposition of transformer insulating oil
will get enough time to dissolve in the oil. Hence by only monitoring the
Buchholz relay it is not possible to predict the condition of the total internal
healthiness of electrical power transformer. That is why it becomes necessary to
analyse the quantity of different gasses dissolved in transformer oil in service.
Actually in dissolved gas analysis of transformer oil or DGA of transformer oil
test, the gases in oil are extracted from oil and analyze the quantity of gasses in a
specific amount of oil. By observing percentages of different gasses present in
the oil, one can predict the internal condition of transformer.
Generally the gasses found in the oil in service are hydrogen (H2), methane(CH4),
Ethane (C2H6), ethylene(C2H4), acetylene (C2H3), carbon monoxide (CO), carbon
dioxide (CO2), nitrogen(N2) and oxygen(O2).
EQUIPMENT IN WHICH OIL IS STORED DISSOLVED GAS ANALYSIS
KIT

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GAS APPROVED
LIMIT(ppm)
H2 100
CO2 2500
C2H2 2
CO 350
C2H4 50
C2H6 65
CH4 120
RESULT OF SAMPLE OIL
BREAKDOWN VOLTAGE TEST
Dielectric strength of transformer oil is also known as breakdown voltage of
transformer oil or BDV of transformer oil. Break down voltage is measured by
observing at what voltage, sparking strands between two electrodes immerged in
the oil, separated by specific gap. low value of BDV indicates presence of

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moisture content and conducting substances in the oil. In this kit, oil is kept in a
pot in which one pair of electrodes are fixed with a gap of 2.5 mm between them.
Now slowly rising voltage is applied between the electrodes. Rate of rise of
voltage is generally controlled at 2 KV/s and observe the voltage at which
sparking starts between the electrodes.
That means at which voltage dielectric strength of transformer oil between the
electrodes has been broken down. Generally this measurement is taken 3 to 6
times in same sample of oil and the average value of these reading is taken.
Minimum breakdown voltage of transformer oil or dielectric strength of
transformer oil at which this oil can safely be used in transformer, is considered
as 50 KV.
BDV KIT
 INSULATION RESISTANCE TEST (MEGGER TEST)
The insulation resistance (IR) test (also commonly known as a Megger) is a spot
insulation test which uses an applied DC voltage (typically either 250V dc, 500V
dc or 1,000V dc for low voltage equipment <600V and 2,500V dc and 5,000V dc
for high voltage equipment) to measure insulation resistance in either KΩ, MΩ or
GΩ. Test should be run between each winding and ground and between each pair
of winding. Low resistance value indicates that the transformer is the problem.

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Polarization index is a variation of the IR test. It is the ratio of IR measured after
voltage has been applied for 10 minutes (R10) to the IR measured after one
minute (R1), i.e.
PI = R10/R1
Low value of PI indicates that the winding may have been contaminated with oil,
dirt etc. or absorbed moistures.
IR is measured with a ‘mega-ohmmeter’. Sometimes this is called Megger Tester
after the name of the instrument first developed for this purpose. Mega-ohmmeter
generates and applies a regulated DC supply. It measures the flow of current and
IR is directly read on its dial.
In general IR & PI test are an excellent means of ascertaining winding conditions that are
contaminated or soaked with moisture. The tests are also good detecting major flaws
where the insulation is cracked or has been cut through. The test can also detect thermal
deterioration for form wound stators using thermoplastic insulation system.
Polarization
index
Condition
of
winding
Measures to
be taken
<1 Hazardous Dry winding
1-1.5 Bad Dry winding
1.5-2 Doubtful Drying is
recommended
2-3 Adequate
3-4 Good
>4 Excellent

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PROTECTION OF TRANSFORMER
1) Breather- Most of the power generation companies use silica gel breathers
fitted to the conservator of oil filled transformers. The purpose of these silica
gel breathers is to absorb the moisture in the air sucked in by the transformer
during the breathing process.
When load on transformer increases or when the transformer under full load,
the insulating oil of the transformer gets heated up, expands and gets expel out
in to the conservator tank present at the top of the power transformer and
subsequently pushes the dry air out of the conservator tank through the silica
gel breather. This process is called breathing out of the transformer.
When the oil cools down, air from the atmosphere is drawn in to the
transformer. This is called breathing in of the transformer.
During the breathing process, the incoming air may consist of moisture and
dirt which should be removed in order to prevent any damage. Hence the air is
made to pass through the silica gel breather, which will absorb the moisture in
the air and ensures that only dry air enters into the transformer. Silica gel in
the breather is blue when installed and they turn to pink colour when they
absorb moisture which indicates that the crystal should be replaced. These
breathers also have an oil cup fitted with so that dust particles get settled
down.

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2) Radiator- When an electrical transformer is loaded, the current starts
flowing through its windings. Due to this flowing of electric current, heat is
produced in the windings, this heat ultimately rises the temperature of
transformer oil. We know that the rating of any electrical equipment depends
upon its allowable temperature rise limit. Hence, if the temperature rise of the
transformer insulating oil is controlled, the capacity or rating of transformer
can be extended up to significant range. Oil immersed power transformer is
generally provided with detachable pressed sheet radiator with isolating valves.
The working principle of radiator is very simple. It just increases the surface
area for dissipating heat of the oil. In case of electrical power transformer, due
to the transport limitation, these units are sent separately and assembled at site
with transformer main body.
Under loaded condition, warm oil increases in volume and comes to the upper
portion of the main tank. Then this oil enters in the radiator through top valve
and cools down by dissipating heat through the thin radiator wall. This cold
oil comes back to the main tank through the bottom radiator valve. This cycle
is repeated continuously till the load is connected to the transformer.
Dissipation of heat in the transformer radiator; can be accelerated further by
force air provided by means of fans. These fans are fitted either on the radiator
bank itself or fitted nearby the bank but all the fans must be faced towards the
radiator.
Sometime, the
cooling rate of
convectional
circulation of
oil is not
sufficient. That
time an oil
pump may be
used for
speeding up
circulation.
Oil temperature indicator
600
-650
– ALARM – FAN ON
900
-950
– TRANSFORMER TRIP

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3) CONSERVATOR TANK- This is a cylindrical tank mounted on
supporting structure on the roof the transformer main tank. The main function
of conservator tank of transformer is to provide adequate space for expansion
of oil inside the transformer. When volume of transformer insulating oil
increases due to load and ambient temperature, the vacant space above the oil
level inside the conservator is partially occupied by the expanded oil.
Consequently, corresponding quantity of air of that space is pushed away
through breather. On other hand, when load of transformer decreases, the
transformer is switched off and when the ambient temperature decreases, the
oil inside the transformer contracts.
CONSERVATOR
INSIDE VIEW OF A CONSERVATOR

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4) BUCHHOLZ RELAY- Buchholz relay in transformer is an oil container
housed the connecting pipe from main tank to conservator tank. It has mainly
two elements. The upper element consists of a float. The float is attached to a
hinge in such a way that it can move up and down depending upon the oil
level in the Buchholz relay Container. One mercury switch is fixed on the
float. The alignment of mercury switch hence depends upon the position of the
float.
The Buchholz relay working principle of is very simple. Buchholz relay
function is based on very simple mechanical phenomenon. It is mechanically
actuated. Whenever there will be a minor internal fault in the transformer such
as an insulation faults between turns, break down of core of transformer, core
heating, the transformer insulating oil will be decomposed in different
hydrocarbon gases, CO2 and CO. The gases produced due to decomposition
of transformer insulating oil will accumulate in the upper part the Buchholz
container which causes fall of oil level in it. Fall of oil level means lowering
the position of float and thereby tilting the mercury switch. The contacts of
this mercury switch are closed and an alarm circuit energized. Sometime due
to oil leakage on the main tank air bubbles may be accumulated in the upper
part the Buchholz container which may also cause fall of oil level in it and
alarm circuit will be energized. By collecting the accumulated gases from the
gas release pockets on the top of the relay and by analyzing them one can
predict the type of fault in the transformer.

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TRANSFORMER NOISE (HUMMING NOISE)
Transformer noise is caused by a phenomenon which causes a piece of magnetic sheet
steel to extend itself when magnetized. When the magnetization is taken away, it goes
back to its original condition. This phenomenon is scientifically referred to as
magnetostriction. A transformer is magnetically excited by an alternating voltage and
current so that it becomes extended and contracted twice during a full cycle of
magnetization.
The magnetization of any given point on the sheet varies, so the extension and
contraction is not uniform. A transformer core is made from many sheets of special steel
to reduce losses and moderate the ensuing heating effect. The extensions and
contractions are taking place erratically all over a sheet and each sheet is behaving
erratically with respect to its neighbor. Applying voltage to a transformer produces a
magnetic flux, or magnetic lines of force in the core. The degree of flux determines the
amount of magnetostriction and hence, the noise level
TRANSFORMER
SOUND
CORE SOUND
MAGNETOSTRICTIVE
FORCES
MAGNETIC FORCES
SOUNDLOAD
WINDINGS STRUCTURAL PARTS
TANK AND WALL
SHUNTS
SOUND GENERATED
BY COOLING
EQUIPMENTS
COOLING FANS AND
PUMPS

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SAFETY MEASURES
• Safety helmets
• Fire extinguishers
• Emergency Exit
• First Aid Box
• Shock proof circuit system
• Maintenance of machines at regular interval
• Proper circuit breakers to protect instruments
• Welding goggles should be used during welding
• Proper alarm system
• Safe distance from rolling parts of the machines
• Safety training & tips to employees
• Arrangements for sufficient and pure drinking water
• Healthy environment for all workers
• Proper lighting system
• Proper ventilation

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CONCLUSION
The first phase of in-plant training has proved to be fruitful. It provides
opportunity to experience the working environment of such huge plant
comprising high-tech machineries.
It provides an opportunity to learn how lean low technology used at proper
place and time can save a lot of time. The employees in the plant helped a lot
and shared useful knowledge.
In- plant training has allowed the student to get an exposure for the practical
implementation to theoretical fundamentals, which would be of great use in
coming future.