sarvesh training report final

8/4/2019 Sarvesh Training Report Final

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A Report on Vocational Training

in NTPC-Singrauli

Shaktinagar, Sonebhadara (U.P.)

Guided By:- Presented By:-Mr. Brajesh Kumar Sarvesh Yadav

Dy. Supdt. (C&I) B.Tech. (EEE)


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S.S.T.P.S. Roll- 0805621057

Acknowledgement

I am very grateful and thankful to all those who were a part of this

project and helped me towards its smooth and efficient completion. I feel

especially thankful to Mr.Brijesh kumar and many others for their helpful

contribution and knowledge without which my project would not be a

reality. I am also thankful to my friends to encourage me & who helped me

to learn such valuable things.

SARVESH YADAV

B.Tech. 4th Year

(ELECTRICAL &ELECTRONIC ENGINEERING)

N.I.E.C.(LUCKNOW)

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CONTENT

About Singrauli Super Thermal Power Station

Introduction

Types of Power Generating Plants

Journey From coal to Electricity

BOILER AND ITS AUXILIARIES

GENERATOR AND ITS AUXILIERIES

SWITCHYARD

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About Singrauli Super Thermal Power Station

Set up in 1975 NTPC, the MAHANAVARATNA Power Company of the country,

and rank 6th, largest thermal power generating utility in the world.

Every 4th Bulb of India is lit by NTPC

SSTPS is the flageship station of NTPC. Its total generating capacity is

2000MW. It is located at a distance of 200KM south from varanasi on the bank

of Gobind Ballabh Pant Sagar in Shaktinagar at Sonebhadra District in Uttar

Pradesh.

In Singrauli there are two(02) stage of power generating units.In St-I there are

fives(05) units of 200 Mw ,while in St-II two (02) units of 500 Mw.

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Introduction

Development of a country like India depends much upon its industrial developmentwhich, in turn, depends upon the development of infrastructures required to carry out

industrial activity. Power ( Electricity) is one of the most important requirement in

infrastructure. Power sector, therefore, has to play a very important role in

development.

Types of Power Generating Plants

1.Thermal:-

Turbine is rotated by steam in this type of power plant. Fuel

used coal or gas.

2. Hydro:-

Turbine is rotated with the help of water jet.

3. Nuclear:-

Turbine is rotated by steam . Fuel used radio-active elements.

4. Renewable:-

Used non-conventional energy sources.

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Why Coal Based Thermal Power Plants Are WidelyUsed In India?

Advantages of Coal Fuel-

Abundantly available in India

Low cost

Technology for Power Generation well developed.

Easy to handle, transport, store and use

Shortcomings of Coal-

Low Calorific Value

Large quantity to be Handled

Produces pollutants, ash

Disposal of ash is Problematic

Reserves depleting fast

Indias Coal Reserves are estimated to be 206 billion tonnes. Presentconsumption is about 450 million tonnes.

Cost of coal for producing 1 unit of electricity (Cost of coal Rs

1000/MT)is Rs 0.75.

Cost of Gas for producing 1 unit of electricity (Cost of Gas Rs

6/SMC)is Rs 1.20.

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Coal MinCoal MinCoal

Journey From coal to Electricity

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W a tW a t

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BOILER AND ITS AUXILIARIESMECHANICAL STEAM GENERATOR:

The steam generator for this plant has a

primary steam flow of 700t/hr. at 139kg/square cm. & 535 degree C at superheatedoutlet. It has 11000 MT of weight.

The boiler is tangentially fired, balanced draught, natural circulation,

radiant single reheat, dry bottom, open door type & direct fired with Indian

bituminous pulverized coal. The steam generator has single drum equipped with steam

purifying unit such as cyclone. To limit the carry-over of dissolved solids to the

stipulated requirement the drum supplies the water to the water walls adequately

through the down comers so as to permit the unrestricted circulation.

The main boiler has following accessories:1: FURNACE:

Steam generator has a single furnace with negative draught, with fusion

welded panels having width of 13.868 m and depth of 10.529 m. Furnace is made of

water walls of 60.5 dia. and 6mm thickness of carbon steel. The rear wall has a goose

neck formation. Additional heating area is provided by 4 platen water walls suspended

on front at the top of the combustion chamber. Furnace is fired with the help of 24

tilting type tangentially fired burners located in each corner of furnace at 6 different

elevations interposed between coal burners. There are 3 oil burners in each corners of

furnace to ignite the crushed coal incoming from coal burners.

2: ECONOMIZERS:

The economizer is continuos unfinned loop type & water flows

in upward direction & gas is in the downward direction. This is a good proposition as

it is used to recover the heat of exit flue gases economically by using plane

economizer tubes. Modern size of economizers is relatively small as compared to

earlier economizers. Since in modern plant feed water heaters are used to increase the

feed water temperature and efficiency of turbine unit

3) BOILER DRUM:

The boiler drum serves two functions:

1) To separate steam from the mixture of water and steam discharged into it.

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2) To house all the equipments used for purification of steam after being separated

from water. This equipment is commonly known as drum internals. Boiler drum

is made of C steel plates. The quantity of water contained in the boiler below the

water level is relatively small as compared to the total steam outlet as result,

regardless the drum size, the worthy point to be noted is that the drum size is not

primarily determined by the water storage. It is determined by the space required to

accommodate the steam separating and purifying equipments. The steam space

provided should be significant to prevent priming and foaming. Drum diameter and

length should be sufficient to provide accessibility for installation, inspection &

servicing of the drum internals. The drum length depends on furnace width or

steam separating devices. For this purpose the drum length is kept at least 900 mm

more than the furnace width.

The technical data about drum for 200 MW and 500 MW units is given respectively as

follows:Weight: 127 & 237 MT (metric tones).

Length: 17 & 22 mt.

Made of: 1676 & 2130 mm OD, 133 & 152.4 mm thickness steel plates.

Location at: 53.340 & 72 mt. from ground level.

The function of drum internals is to separate water and steam from the mixture

generated in water walls. The drum internals reduces the dissolved solids of the steam

to below the acceptable limit of 1 ppm.

4: WATAR WALLS AND DOWN COMERS:

Water walls and down comers serve asthe only means of heating & evaporating the feed water supplied to the boiler from the

economizer. Water walls consist of tangential vertical tubes & are connected at the top

& bottom to the headers. These tubes receive water from the boiler drum by means of

down comers connected between water walls lower header and drum. In a boiler

approx. 50% of heat released by the combustion of fuel in the furnace is absorbed by

the water walls. Heat so absorbed by the water walls is used in evaporation of water

supplied by the boiler drum. The mixture of steam & water is discharged from the top

of the water walls tubes into the upper wall header & then passes through the riser

tubes to the steam drum where the steam is separated from water & the accompanying

water together with in coming feed water is returned to the water walls through thedown comers.

5: SUPER HEATERS:

Super heating is done in 3 phases by radiation & convection

mode of heat transfer. The super heaters are continuous tube type with the horizontal

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primary section located above the economizer & pendant platen secondary section at

furnace exit i.e. the convective SH is suspended in the second pass, the radiant SH is

in the radiant zone & final SH is between first and second pass.

The side panels of first pass & roof of the first & second pass both also

from the super heating surface. A spray type attemporator is also envisaged to control

the super heater outlet temperature for varying load.

Classification of super heaters:

The super heaters are classified on the basis of:

1: Position and shape:

1) Pendant type SH.

2) Horizontal type SH.

3) Platen type SH.

2: Method of heat receiving:

1) Radiant type SH.

2) Convection type SH.

3) Combined SH.

Super heaters are meant to raise the temperature of the saturated steam absorbing the

heat from flue gas & thus increase the cycle efficiency economically.

There are 4 sections of SH:

1) Roof section-located above the furnace with radiation mode heat transfer.

2) Steam cooled-made of 51mm OD tubes forms all 3(side, front, rear) walls &

roof of vertical gas pass.

3) Platen-directly above the furnace consisting of 29 assemblies of 51 mm OD

tube by radiation h/t.

4) Pendant located behind screen tube & is connected between super heater

vertical spaced inlet & outlet header.

5) Convection horizontal-located in rear vertical gas pass above the

economizer. It is called LTSH (Low Temperature Super Heater).

Saturated steam from drum = LTSH (via roof section SH and steam

cooled walls) = Platen SH (through inter stage de-super heater) = pendant

convection type SH =Turbine (via 2 MS lines of 323.9*42 square mm connected to

2 ends of SH).

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6: REHEATER:

Reheater is used for further increasing the cycle thermal efficiency by

raising the temperature of already expanded steam up to 540 degree C again. It is

placed in the hotter zone so that minimum surface requirement is kept.Reheating is done by pendant type of coils of the RH suspended

vertically inside the furnace between platen & exit of super heater. Reheater

temperature is 535 degree C at 582 tones/hr. at 24.5 cm 2 pressure. Burner tilt is used

for controlling Reheater temperature.

This is a part of boiler which receives steam back from the turbine after

it has given up some of its energy in the high pressure section of the turbine. The

Reheater raises the temperature of this steam, usually to its original value, for further

expansion in the turbine. The purpose of this reheating is to add energy to the partially

used steam.

7: BURNERS:

In stage 1, there are 24 total pulverized coal burners for corner fired

C.E. type boiler & 12 oil burners provided each in between 2 coal burners.

The pulverized coal burners are arranged in such a way that 6 mills supply

the coals to the burners at 4 corners of the furnace. All the nozzles of the burners are

interred linked & can be tilted as a single unit from 30 to -30 degree.

The oil burners are fed with heavy fuel oil till boiler load reaches to about 25%.

8: IGNITERS:

Igniters are used for lighting the main oil gun. In stage 1, there are 2

igniters air fans which supplies air for combustion of igniters oil.

Mainly 2 types of igniters are used:

1) Eddy plate igniters.

2) High energy arc type igniters.

There are 12 side HEA type igniters for boiler. The atomizing air for

igniters is taken from plate air compressor at 7 kg/square cm (gauge). The burners arelocated at 3 elevations. Each elevation has 4 oil burners & igniters. These elevations

are normally known as AB elevation, CD elevation & EF elevation.

In our plant HEA igniters have been used. It can directly ignite the heavy

fuel oil.

The main part of these igniters:

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1) An Exciter unit: this stores the energy and releases it at a high voltage & for

short duration.

2) A spark rod which is designed to convert the electrical energy into an intensive

spark.

3) A pneumatically operated retracts mechanism which is used to position the

spark in the firing position & to retract it in non firing position.

9: AIR PRE HEATERS:

For stage 1, there are 2 no. of trisector, regenerative type

air pre heaters forming 2 parallel passes and heating the primary air and secondary air

with flue gases. It has 900 square m surfaced of heating are a pre air heaters. Theses

are electrically rotated at 14 rpm. 4 no. of swiveling type soot blowers with steam as

media are used to remove the soot from APH. 2no. of steam coil APH are also used

with medium as secondary air at FD fan discharge with heating surface area 770

square m per air heater. There are 2 sets of each of FD, ID & PA fans.Air pre heating is done by the rotation of rotor with 14 rpm. When the

coils of pre heater comes in contact with hot flue gases from furnace they absorbs the

energy of flue gases with the rotation of coils this energy is transferred to the second

pass air heading towards the furnace again for combustion.

10: DE-SUPER HEATER:

These are direct spray type de super heaters. Two DSHs

are located between rear horizontal outlet header & platen inlet header & CRH

towards RH inlet header. These are used to reduce the steam temperature when

necessary & to maintain the temperature at designed value.

It is done by injecting water spray into the path of the steam through a

nozzle at the entering end of the DSH. Spray water source is from boiler feed water

system, in order to prevent chemical deposition in the super heater & RH & carry over

of the solids to the turbine.

11: FANS:

There are many types of fan used in the power plant; some of them are

given as follows for stage 2:

1: PA FAN:

Primary Air fan is used to suck the air from atmosphere to deliver it tothe coal mills to fly the pulverized coal from coal mills to the furnace. There are two

passes provided through PA fan, hot & cold air pass with the help of their mixture we

control the humidity in coal. The PA fan having radial design with over hung

impeller, coupled with motor & having inlet vane control.

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PRINCIPLE:

It is based on the energy transformation principle due to centrifugal

forces. Some amount of the velocity energy is converted into pressure energy in the

spiral casing.

2: FD FAN:

Forced draught fan is used to supply the air for combustion in the furnace.

This air is called secondary air which is being supplied with the help of 2 no. of axial

reaction FD fans with variable pitch control coupled with motor.

3: ID FAN:

Before stack, one no. of impulse type ID fan with inlet vane control

coupled with motor is provided for each stream. Fans have been designed for 60%

MCR flow conditions of the boiler keeping in view the specified coal characteristics.

PRINCIPLE:

This fan works according to impulse energy principle. The major part of

the energy transformed to the gas is velocity energy after the impeller. The velocity

energy is converted into pressure energy by diffuser. Flow is controlled by changing

the direction of gas entering to the impeller blades by providing adjustable guidevanes.

12: AUXILIARY BOILER:

To provide steam at 16 kg/square cm & at 215 degree C to

various auxiliaries at initial stages of the operation of the main plant & for heating the

heavy fuel oil of 10500 kcal/kg HCV a package type aux. boiler of 55 tones/hr.

capacity has been installed. It is front fixed, natural circulation, bi drum boiler with

bottom support.

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GENERATOR AND ITS AUXILIERIES

The generator is of 3 phase, 2 pole, cylindrical rotor, and 3000 rpm. For stage 1, Therated o/p is 235.3 MVA at 0.85 pf. The terminal voltage is 15.75 Kv at 50 Hertz

frequency at .5 SCR & 8625 Ampere current. Stator winding is designed for

connection in double star with 3 phase and 6 neutral terminals brought out on the slip

rings side. The terminal brushings are of porcelain & housed in the lower part of stator

terminal box made of non magnetic steel plates. The stator body is totally enclosed

gas tight, explosion proof fabricated structure. The shaft and the body are forged in the

one piece of Cr-Mo-V steel. The rotor is balanced to a high accuracy & subjected to

20% over speeding for 2 minutes as per standards. The field windings consist of

formed coils made up of hard drawn silver bearing copper with bonded insulation.

Gap pick up system is employed for direct hydrogen cooling of rotor winding.

HYDROGEN COOLING SYSTEM:

The rotor winding is cooled by hydrogen flowing

through the radial ventilating ducts. It is designed for hydrogen pressure up to 3

kg/square cm gauge. Hydrogen is cooled by gas cooler mounted on the stator body.

Hydrogen cooling water is cooled by suitable water to water heat exchanger external

to machine.

Since hydrogen is of lower density than air & superior thermal properties. The stator

temperature limit is 105 degree C.

WATER COOLING SYSTEM:

The stator is cooled by the circulating D.M. water

through hollow conductors. The system is designed to maintain a constant rate of

cooling water flow to the stator windings at a nominal water inlet temperature of 40

deg. C.

The cooling water is again cooled by water which is also demineralised

to avoid contamination with any impure water in case of cooler tube leakage. The

cooling water is in turn cooled by clarified water taken from clarified water header.

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SEAL OIL SYSTEM:

Shaft seal operating with a flow of oil under pressure are used

to prevent the escape of hydrogen along with generator shaft. A pressure regulating

valve maintains a constant differential pressure of seal oil over hydrogen pressure in

the generator. Vacuum treated oil from the seal oil supply unit is fed to the center ofthe seal ring assembly from where it flows between rings and shaft in the both

direction, and a film thus established in the constricted area prevents the leakage of

hydrogen. A SOP is provided for maintaining pressure.

EXCITATION:

To have increased transient stability & capability of generator in

leading p.f. zone a fully static thyristorized excitation system is provided.

Power required for excitation system is tapped off from generator bus

duct, steeped down, rectified in thyristor bridges & fed to the generator slip rings.

During start up the system shall be fed from the station AC power suitably rectified bya separate rectifier.

BUS BARS:

Generator main bus bars consist of natural air cooled, continuous

enclosure type isolated phase bus. There is no connection between generator and main

transformer. Al alloy is for conductor material.

GENERATOR T/F:

For each unit of 200 MW, one 250 MVA, 15.75 KV/400 KV, 3 phase, out door type t/f has been installed in the t/f yard. It is connected to the

generator through isolated phase duct. LV winding is delta connected & HV winding

is star connected. The percentage impedance is about 14%. The GT is oil cooled.

Rating is 250 MVA, quantity is 5, type is of two windings, VR (voltage ratio) is 15.75

KV/400 KV and temperature rise is 40 deg. C by oil and 60 deg. C by windings.

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RELAY :

Protective relays are devices that detect abnormal conditions in electrical circuits byconstantly measuring the electrical quantities.

The basic quantities, which may change during faulty conditions, are voltage, current,

frequency, phase angle etc.

It disconnects the faulty parts as quickly as possible.

It disconnects the faulty part from the healthy part, causing least disturbance to the

healthy system.

It sounds an alarm, so that the operator may take some corrective action.

COST OF ELECTRICITY :

The direct cost of electric energy produced by a thermal power station is the result of

cost of fuel, capital cost for the plant, operator, labor, maintenance, and factors such as

ash handling and disposal.

Indirect, social or environmental costs such as the economic value of environmental

impacts, or environmental and health effects of the complete fuel cycle and plant

decommissioning, are not usually assigned to generation costs for thermal stations in

utility practice, but may form part of an environmental impact assessment.

In now a day A.B.T(Availability Based Tariff) concept is used by grid for pay the cost

of generated electricity by power house .In this system power house has to declare its

availability of Mega Units generation for next 24 hours and if power house get fail

then penalty is forced on it and in some special circumstance if power demand

increase and power house helps to over-come this problem then for this extra amount

is pay on increased rate . This whole concept is based to balance the difference

between demand and supply because power is unique commodity and it cannot be

seen ,store and packed .

SWITCHYARD

It is a switching station which has the following credits :

Main link between generating plant and Transmission system, which has a large

influence on the security of the supply.

Step-

Up and/or Step-down the voltage levels depending upon the Network Node.

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Switching ON/OFF Reactive Power Control devices, which has effect on

Quality of power.

SWITCHYARD EQUIPMENTS

Following equipments are used in switchyard :

Lightening arrestor

Current transformer

Voltage transformer

Power transformers / I.C.T.

Bus bar and clamp fittings

Support structure

Isolators

Circuit BreakerWave traps

Earthling switch

FUNCTION OF VARIOUS EQUIPMENTS USED:

Transformers :

- Transforms the voltage levels from higher to lower level or vice versa, keeping the

power constant.

Circuit breakers :

- Automatically breaks the electrical circuits under loaded condition.

Isolators

OPERATES UNDER NO LOAD CONDITION

INTERLOCKED WITH BREAKERS AND EARTHSWITCHES SHOULD WITHSTAND EXTREME WIND PRESSURES

MOTOR DRIVEN AND HAND DRIVEN

LOCAL AS WELL AS REMOTE OPERATION POSSIBLE

ISOLATES SECTIONS FOR MAINTENANCE

USED TO SELECT BUS BARS

CT SWITCHING FOR BUS BAR PROTECTION

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Instrument transformers :

- For stepping-down the electrical parameter (Voltage or Current) to a lower and safe

value for Metering and Protection logics.

Earth switch :

- Used to connect the charged body to ground to discharge the trapped charge to havea safe maintenance zone.

Lightning arrestors :

The distance of L.A. from Generator Transformer should be as minimum as possible

to avoid passing of traveling surges to Generator Transformer. However, it should not

be too close to cause damage to transformer bushing in case of shattering of LAs.

Further possibility of using shatter proof L.As needs to be checked in the market.

It is observed that the counter / leakage current monitors of most of the L.As are not

operating properly only due to breakage of glass or rusting of enclosures or entry of

dust / water in the enclosures. It is necessary to provide rugged enclosures with IP67

degree of protection. Further the leakage current measured at works should be

indicated on the name plate. In case the leakage current increases more than two times

the factory recorded current, the L.A. should be replaced

Overhead earth wire :

- Protects the overhead transmission line from Lightning strokes.

Bus bar:

- Conductors to which a number of circuits are connected.

Wave Traps/Line traps :

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- Wave trap is used for Protection of the transmission line and communication

between the Substations.

Reactive Power control devices :

- Controls the reactive power imbalance in the grid by switching ON/OFF the Shunt

Reactors, Shunt Capacitors etc.

Current Limiting Reactors :

- Limits the Short circuit currents in case of faulty conditions.

CURRENT TRANSFORMERS

Current transformers are used to step-down the high magnitude of current to a safe

value for Measuring and Protection logics

Current transformers are used for the instrumentation, protection or metering of

power systems.

VOLTAGE TRANSFORMERS :

Voltage transformers are to step-down the high magnitude of voltage to a safe value

for Measuring and Protection logics.

Voltage transformers serve a number of functions in a power system. They are

required for the operation of many types of instrumentation and relay protective

Factors effecting the selection of Switching Scheme

System Security

Operational Flexibility

Simplicity of Protection arrangements

Ability to limit the Short Circuit levels

Maintenance

Ease of extension

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Total land area Cost

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