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CHAPTER-1

INTRODUCTION OF NTPC

1.1 INTRODUCTION

NTPC Limited (Company) was incorporated in November 1975 with the objective to

plan and promote development of thermal power in the country. In May 1998, NTPC

diversified its objectives to include new business activities like development of hydro

power and power through nonconventional or renewable energy sources. As on 31 March

2010, NTPC with an installed power generating capacity of 28,902 mega watt (MW)

from 15 coal based thermal power stations and seven gas/liquid fuel based power stations

was the largest thermal power generating company of the country. NTPC contributed 28

per cent of the total electricity generation of the country as of 31 March 2010. NTPC is a

Government Company wherein Government of India holds 84.50 per cent of the total

equity.

In line with the objective of National Electricity Policy (February 2005) to increase

annual per capita consumption of electricity from the existing level of 631 units to 1,000

units, NTPC planned (April 2007) a Capacity Addition Programmed to become a

50,000MW Company by 2012. Since, NTPC had installed capacity of 27404 MW up to

31st March 2007, the Company planned to increase the capacity by 22,600 MW (83

percent) during next five years (2007-2012). However, due to non-fructification,

rescheduling or substitution, the Company revised (2007-08) its target downward to

22,430 MW to be achieved during 2007-2012. In order to achieve this target, NTPC

decided (2006-07) to adopt a multi-pronged growth strategy. A list of projects identified

for capacity addition during the above period is placed at Annexure-I based on type of

fuel to be used (i.e. Thermal, Hydro or Wind) and nature of project (i.e. Greenfield or

Expansion).

The Management stated (November 2010) that the capacity addition target of 22,430 MW was approved

neither by the Planning Commission nor by the Ministry of Power. Analysis should be done only against

the target for capacity addition of 17,760 MW fixed by Planning Commission for NTPC for 11th Plan.

We do not agree with the Management as the capacity addition target of 22,430 MW was set by the

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Company itself as per the Corporate Plan. The Company had in fact identified projects to augment

capacity for 22,430 MW during 2007-12 and had also initiated action on these projects.

Of the target of 22,430 MW fixed involving 24 projects, the Company commissioned only five thermal

projects involving 4,220 MW (19 percent) till August 2010 of which Ratnagiri project was a revival

project. Further, out of above target, two projects involving 760 MW have not been so far (August 2010)

awarded. Out of balance 17,450 MW involving 17 projects, the size of Muzaffarpur Expansion project

was reduced by 110 MW. The Company anticipates achieving another 5,000 MW out of 17,340 MW on

firm basis by March 2012.

Thus, against the target of 22,430 MW, Company would be able to achieve only 9,220 MW resulting in a

shortfall of 13,210 MW (59 per cent). Analysis of progress made so far reveals that although the

Company anticipates to achieve additional 4,530 MW involving six projects on best effort basis,

commissioning of these projects appears to be difficult by March 2012 as present status of progress of

work is far from satisfactory.

1.2 INSTALLED CAPACITY $ GENERATION

Fig. 1.1 GROWTH OF NTPC

In October 2004, NTPC launched its Initial Public Offering (IPO) consisting of 5.25% as

fresh issue and 5.25% as offer for sale by Government of India. NTPC thus became a

listed company in November 2004 with the Government holding 89.5% of the equity

share capital. In February 2010, the Shareholding of Government of India was reduced

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from 89.5% to 84.5% through Further Public Offer. The rest is held by Institutional

Investors and the Public.

Fig. 1.2 NTPC CONTRIBUTION IN GENERATION

1.3 STRATEGIES

Fig. 1.3 STRATEGIES

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1.3.1 TECHNOLOGICAL INITIATIVES

Introduction of steam generators (boilers) of the size of 800 MW.

Integrated Gasification Combined Cycle (IGCC) Technology.

Launch of Energy Technology Centre -A new initiative for development of

technologies with focus on fundamental R&D.

The company sets aside up to 0.5% of the profits for R&D.

Roadmap developed for adopting Clean Development.

Mechanism to help get / earn Certified Emission Reduction.

1.3.2 CORPORATE SOCIAL RESPONSIBILITY

As a responsible corporate citizen NTPC has taken up number of CSR initiatives.

NTPC Foundation formed to address Social issues at national level

NTPC has framed Corporate Social Responsibility Guidelines committing up

to0.5% of net profit annually for Community Welfare.

The welfare of project affected persons and the local population around NTPC

projects are taken care of through well drawn Rehabilitation and Resettlement

policies.

The company has also taken up distributed generation for remote rural areas

1.3.3 PARTNERING GOVERNMENT IN VARIOUS INITIATIVES

Consultant role to modernize and improvise several plants across the country.

Disseminate technologies to other players in the sector.

Consultant role Partnership in Excellence Programmed for improvement of PLF

of 15 Power Stations of SEBs.

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Rural Electrification work under Rajiv Gandhi Garmin Vidyutikaran.

1.3.4 ENVIRONMENT MANAGEMENT

All stations of NTPC are ISO 14001 certified.

Various groups to care of environmental issues.

The Environment Management Group.

Ash utilization Division.

A forestation Group.

Centre for Power Efficiency & Environment Protection.

Group on Clean Development Mechanism.

NTPC is the second largest owner of trees in the country after the Forest

department

1.4 VISION

To be the worlds largest and best power producer, powering Indias growth.

1.5 MISSION

Develop and provide reliable power, related products and service at competitive prices,

integrating multiple energy sources with innovative and eco-friendly technologies and

contribute to society.

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1.6 JOURNEY OF NTPC

Fig. 1.4 JOURNEY OF NTPC

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CHAPTER-2

ABOUT BADARPUR THERMAL POER STATION

2.1 INTRODUCTION

BADARPUR THERMAL POWER STATION was established on 1973 and it was the

part of Central Government. On 01/04/1978 is given as No Loss No Profit Plant of

NTPC. Since then operating performance of NTPC has been considerably above the

national average. The availability factor for coal stations has increased from 85.03 % in

1997-98 to 90.09 % in 2006-07, which compares favorably with international standards.

The PLF has increased from 75.2%in1997-98 to 89.4% during the year 2006-07 which is

the highest since the inception of NTPC.

Badarpur thermal power station started with a single 95 mw unit. There were 2 more

units (95 MW each) installed in next 2 consecutive years. Now it has total five units with

total capacity of 720 MW. Ownership of BTPS was transferred to NTPC with effect from

01.06.2006 through GOIs Gazette Notification.

The power is supplied to a 220 KV network that is a part of the northern grid. The ten

circuits through which the power is evacuated from the plant are:

1. Mehrauli

2. Okhla

3. Ballabgarh

4. Indraprastha

5. UP (Noida)

6. Jaipur

Given below are the details of unit with the year theyre installed.

Address Badarpur,New Delhi-110044

Installed capacity 720MW

Derated capacity 705MW

Location New Delhi

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Coal Source Jharia coal fields

Water Source Agra Canal

Beneficiary states Delhi

Unit sizes 3*95MW

2*210MW

Units commissioned Unit 1-95MW July 1973

Unit 2-95MW August 1974

Unit 3-95MW March 1975

Unit 4-210MW December 1978

Unit 5-210MW December 1981

International assistance Ownership of BTPS was transferred to

NTPC with

effect from 1-06-2006 GOIs Gazette

notification

Table 2.1 BTPS INFORMATION

2.2 STATION LOCATION

Badarpur is situated only 20 km away from Delhi. The plant is located on the left side of

the National Highway (Delhi-Mathura Road) and it comprises of 430 hectares (678 acres)

bordered by the Agra Canal from East and by Mathura-Delhi Road from West. However,

the area for ash disposal is done in the Delhi Municipal limit and is maintained with the

help of Delhi Development Authority. The plant is also close to the project of 220 kV

Double Circuit Transmission line between the I.P. station and Ballabgarh Cooling Water

is obtained from Agra Canal for the cooling system. Additional 60 cusecs channel has

also been constructed parallel to the Agra Canal so as to obtain uninterrupted watersupply during the slit removing operation in Agra Canal.

2.3 NTPC ENVIRONMENT POLICY

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NTPC is committed to the environment, generating power at minimal environmental cost

and preserving the ecology in the vicinity of the plants. NTPC has undertaken massive a

forestation in the vicinity of its plants. Plantations have increased forest area and reduced

barren land. The massive a forestation by NTPC in and around its Ramagundam Power

station (2600 MW) have contributed reducing the temperature in the areas by about 3c.

NTPC has also taken proactive steps for ash utilization. In 1991, it set up Ash Utilization

Division A.

"Centre for Power Efficiency and Environment Protection- CENPEE" has been

established in NTPC with the assistance of United States Agency for International

Development- USAID. CENPEEP is efficiency oriented, eco-friendly and eco-nurturing

initiative - a symbol of NTPC's concern towards environmental protection and continued

commitment to sustainable power development in India. As a responsible corporate

citizen, NTPC is making constant efforts to improve the socio-economic status of the

people affected by its projects. Through its Rehabilitation and Resettlement programmes,

the company endeavors to improve the overall socio economic status Project Affected

Persons. NTPC was among the first Public Sector Enterprises to enter into a

Memorandum of Understanding-MOU with the Government in 1987-88. NTPC has been

placed under the 'Excellent category' (the best category) every year since the MOU

system became operative. Harmony between man and environment is the essence of

healthy life and growth. Therefore, maintenance of ecological balance and a pristine

environment has been of utmost importance to NTPC. It has been taking various

measures discussed below for mitigation of environment pollution due to power

generation.

NTPC is the second largest owner of trees in the country after the Forest department.

As early as in November 1995, NTPC brought out a comprehensive document entitled

"NTPC Environment Policy and Environment Management System". Amongst the

guiding principles adopted in the document is companys proactive approach to

environment, optimum utilization of equipment, adoption of latest technologies and

continual environment improvement. The policy also envisages efficient utilization of

resources, thereby minimizing waste, maximizing ash utilization and providing green belt

all around the plant for maintaining ecological balance.

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2.3.1 ENVIRONMENT MANAGEMENT, OCCUPATIONAL HEALTH AND

SAFETY SYSTEMS:

NTPC has actively gone for adoption of best international practices on environment,

occupational health and safety areas. The organization has pursued the Environmental

Management System (EMS) ISO 14001 and the Occupational Health and Safety

Assessment System OHSAS 18001 at its different establishments. As a result of pursuing

these practices, all NTPC power stations have been certified for ISO 14001 & OHSAS

18001 by reputed national and international Certifying Agencies

2.3.2 POLLUTION CONTROL SYSTEMS:

While deciding the appropriate technology for its projects, NTPC integrates manyenvironmental provisions into the plant design. In order to ensure that NTPC complies

with all the stipulated environment norms, various state-of-the-art pollution control

systems / devices as discussed below have been installed to control air and water

pollution.

2.3.3 ELECTROSTATIC PRECIPITATORS:

The ash left behind after combustion of coal is arrested in high efficiency Electrostatic

Precipitators (ESPs) and particulate emission is controlled well within the stipulated

norms. The ash collected in the ESPs is disposed to Ash Ponds in slurry form.

2.3.4 LIQUID WASTE TREATMENT PLANTS & MANAGEMENT SYSTEM:

The objective of industrial liquid effluent treatment plant (ETP) is to discharge lesser and

cleaner effluent from the power plants to meet environmental regulations. After primary

treatment at the source of their generation, the effluents are sent to the ETP for further

treatment. The composite liquid effluent treatment plant has been designed to treat all

liquid effluents which originate within the power station e.g. Water Treatment Plant

(WTP), Condensate Polishing Unit (CPU) effluent, Coal Handling Plant (CHP) effluent,

floor washings, service water drains etc.

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CHAPTER-3

OPERATION OF A POWER PLANT

3.1 BASIC PRINCIPLE

As per FARADAYs Law-Whenever the amount of magnetic flux linked with a circuit

changes, an EMF is produced in the circuit. Generator works on the principle of

producing electricity. To change the flux in the generator turbine is moved in a great

speed with steam. To produce steam, water is heated in the boilers by burning the coal.

In a Badarpur Thermal PowerStation, steam is produced and used to spin a turbine that

operates a generator. 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; this is known as a Rankine cycle.

The electricity generated at the plant is sent to consumers through high-voltage power

lines The Badarpur Thermal Power Plant has Steam Turbine-Driven Generators which

has a collective capacity of 705MW. The fuel being used is Coal which is supplied from

the Jharia Coal Field in Jharkhand. Water supply is given from the Agra Canal.

3.2 BASIC STEPS OF ELECTRICITY GENERATIONThe basic steps in the generation of electricity from coal involves following steps:

Coal to steam

Steam to mechanical power

Mechanical power to electrical power

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Fig. 3.1 THERMAL POWER PLANT

3.2.1COAL TO ELECTRICITY:

Fig. 3.2 COAL TO ELECTRICITY

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Fig. 3.3 POWER PLANT CYCLE

3.3 FACTORS AFFECTING THERMAL CYCLE EFFICIENCY

Thermal cycle efficiency is affected by following

Initial stream pressure.

Initial stream temperature.

Whether reheat is used or not, and if used reheat pressure and temperature.

Condenser pressure.

3.4 PARTS OF A POWER PLANT

The various parts are listed below:-

1. COOLING TOWER

2. COOLING WATER PUMP

3. TRANSMISSION LINE (3-PHASE)

4. UNIT TRANSFORMER (3-PHASE)

5.

ELECTRIC GENERATOR (3-PHASE)6. LOW PRESSURE TURBINE

7. CONDENSATE EXTRACTION PUMP

8. CONDENSER

9. INTERMEDIATE PRESSURE TURBINE

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Fig. 3.4 PARTS OF A POWER PLANT

10.STEAM GOVERNOR VALVE

11.HIGH PRESSURE TURBINE 21

12.DEAERATOR

13.FEED HEATER

14.COAL CONVEYOR

15.COAL HOPPER

16.PULVERISED FUEL MILL

17.BOILER DRUM

18.ASH HOPPER

19.SUPER HEATER

20.FORCED DRAUGHT FAN

21.REHEATER

22.

AIR INTAKE

23.ECONOMISER

24.AIR PREHEATER

25.PRECIPITATOR

26.INDUCED DRAUGHT FAN

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27.FLUE GAS

3.4.1 COOLING TOWER

Cooling towers are heat removal devices used to transfer process waste heat to the

atmosphere. Cooling towers may either use the evaporation of water to remove process

heat and cool the working fluid to near the wet-bulb air temperature or in the case of

closed circuit dry cooling towers rely solely on air to cool the working fluid to near the

dry-bulb air temperature. Common applications include cooling the circulating water

used in oil refineries, chemical plants, power stations and building cooling. The towers

vary in size from small roof-top units to very large hyperboloid structures that can be up

to 200 meters tall and 100 meters in diameter, or rectangular structures that can be over

40 meters tall and 80 meters long. Smaller towers are normally factory-built, while larger

ones are constructed on site. The absorbed heat is rejected to the atmosphere by the

evaporation of some of the cooling water in mechanical forced-draft or induced Draft

towers or in natural draft hyperbolic shaped cooling towers as seen at most nuclear power

plants.

3.4.2 COOLING WATER PUMP

It pumps the water from the cooling tower which goes to the condenser.

3.4.3 THREE PHASE TRANSMISSION LINE

Three phase electric power is a common method of electric power transmission. It is a

type of polyphase system mainly used to power motors and many other devices. A three

phase system uses less conductive material to transmit electric power than equivalent

single phase, two phase, or direct current system at the same voltage. In a three phase

system, three circuits reach their instantaneous peak values at different times. Takingcurrent in one conductor as the reference, the currents in the other two are delayed in time

by one-third and two-third of one cycle .This delay between phases has the effect of

giving constant power transfer over each cycle of the current and also makes it possible

to produce a rotating magnetic field in an electric motor.

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At the power station, an electric generator converts mechanical power into a set of

electric currents, one from each electromagnetic coil or winding of the generator. The

current are sinusoidal functions of time, all at the same frequency but offset in time to

give different phases. In a three phase system the phases are spaced equally, giving a

phase separation of one-third of one cycle. Generators output at a voltage that ranges

from hundreds of volts to 30,000 volts.

3.4.4 UNIT TRANSFORMER (3-PHASE)

At the power station, transformers step-up this voltage to one more suitable for

transmission. After numerous further conversions in the transmission and distribution

network the power is finally transformed to the standard mains voltage (i.e. the

household voltage). The power may already have been split into single phase at this

point or it may still be three phase. Where the step-down is 3 phase, the output of this

transformer is usually star connected with the standard mains voltage being the phase-

neutral voltage. Another system commonly seen in North America is to have a delta

connected secondary with a centre tap on one of the windings supplying the ground and

neutral. This allows for 240 V three phase as well as three different single phase voltages(

120 V between two of the phases and neutral , 208 V between the third phase ( or wild

leg) and neutral and 240 V between any two phase) to be available from the same supply.

3.4.5 ELECTRICAL GENERATOR

An Electrical generator is a device that converts kinetic energy to electrical energy,

generally using electromagnetic induction. The task of converting the electrical energy

into mechanical energy is accomplished by using a motor. The source of mechanical

energy maybe water falling through the turbine or steam turning a turbine (as is the case

with thermal power plants). There are several classifications for modern steam turbines.

Steam turbines are used in our entire major coal fired power stations to drive the

generators or alternators, which produce electricity. The turbines themselves are driven

by steam generated in "boilers or "steam generators" as they are sometimes called.

Electrical power stations use large steam turbines driving electric generators to produce

most (about 86%) of the worlds electricity.

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These centralized stations are of two types: fossil fuel power plants and nuclear power

plants. The turbines used for electric power generation are most often directly coupled to

their-generators .As the generators must rotate at constant synchronous speeds according

to the frequency of the electric power system, the most common speeds are 3000 r/min

for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets rotate at

half those speeds, and have a 4-pole generator rather than the more common 2-pole one.

3.4.6 LOW PRESSURE TURBINE

Energy in the steam after it leaves the boiler is converted into rotational energy as it

passes through the turbine. The turbine normally consists of several stages with each

stages consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades

convert the potential energy of the steam into kinetic energy and direct the flow onto the

rotating blades. The rotating blades convert the kinetic energy into impulse and reaction

forces, caused by pressure drop, which results in the rotation of the turbine shaft. The

turbine shaft is connected to a generator, which produces the electrical energy. Low

Pressure Turbine (LPT) consists of 4x2 stages. After passing through Intermediate

Pressure Turbine steam is passed through LPT which is made up of two parts- LPC

REAR & LPC FRONT. As water gets cooler here it gathers into a HOTWELL placed in

lower parts of turbine.

3.4.7 CONDENSATION EXTRACTION PUMP

A Boiler feed water pump is a specific type of pump used to pump water into a steam

boiler. The water may be freshly supplied or returning condensation of the steam

produced by the boiler. These pumps are normally high pressure units that use suction

from a condensate return system and can be of the centrifugal pump type or positive

displacement type. Construction and operation: Feed water pumps range in size up to

many horsepower and the electric motor is usually separated from the pump body by

some form of mechanical coupling. Large industrial condensate pumps may also serve as

the feed water pump. In either case, to force the water into the boiler, the pump must

generate sufficient pressure to overcome the steam pressure developed by the boiler. This

is usually accomplished through the use of a centrifugal pump.

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Feed water pumps usually run intermittently and are controlled by a float switch or other

similar level-sensing device energizing the pump when it detects a lowered liquid level in

the boiler. Some pumps contain a two-stage switch. As liquid lowers to the trigger point

of the first stage, the pump is activated. If the liquid continues to drop, (perhaps because

the pump has failed, its supply has been cut off or exhausted, or its discharge is blocked)

the second stage will be triggered. This stage may switch off the boiler equipment

(preventing the boiler from running dry and overheating), trigger an alarm, or both.

3.4.8 CONDENSER

The steam coming out from the Low Pressure Turbine (a little above its boiling pump) 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.

3.4.9 INTERMEDIATE PRESSURE TURBINE

Intermediate Pressure Turbine (IPT) consists of 11 stages. When the steam has been

passed through HPT it enters into IPT. IPT has two ends named as FRONT & REAR.

Steam enters through front end and leaves from Rear end.

3.4.10 STEAM GOVERNOR VALVE

Steam locomotives and the steam engines used on ships and stationary applications such

as power plants also required feed water pumps. In this situation, though, the pump was

often powered using a small steam engine that ran using the steam produced by the boiler

a means had to be provided, of course, to put the initial charge of water into the boiler

(before steam power was available to operate the steam-powered feed water pump).The

pump was often a positive displacement pump that had steam valves and cylinders at oneend and feed water cylinders at the other end; no crankshaft was required. In thermal

plants, the primary purpose of surface condenser is to condense the exhaust steam from a

steam turbine to obtain maximum efficiency and also to convert the turbine exhaust

steam into pure water so that it may be reused in the steam generator or boiler as boiler

feed water.

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By condensing the exhaust steam of a turbine at a pressure below atmospheric pressure,

the steam pressure drop between the inlet and exhaust of the turbine is increased, which

increases the amount heat available for conversion to mechanical power. Most of the heat

liberated due to condensation of the exhaust steam is carried away by the cooling medium

(water or air) used by the surface condenser. Control valves are valves used within

industrial plants and elsewhere to control operating conditions such as temperature,

pressure, flow and liquid level by fully or partially opening or closing in response to

signals received from controllers that compares a set point to a process variable

whose value is provided by sensors that monitor changes in such conditions. The opening

or closing of control valves is done by means of electrical, hydraulic or pneumatic

systems.

3.4.11 HIGH PRESSURE TURBINE

Steam coming from Boiler directly feeds into HPT at a temperature of 540C and at a

pressure of 136 kg/cm2. Here it passes through 12 different stages due to which its

temperature goes down to 329C and pressure as 27 kg/cm2. This line is also called as

CRHCOLD REHEAT LINE. It is now passed to a REHEATER where its temperature

rises to 540C and called as HRH-HOT REHEATED LINE.

3.4.12 DEAERATOR

A Deaerator is a device for air removal and used to remove dissolved gases (an alternate

would be the use of water treatment chemicals) from boiler feed water to make it

noncorrosive. A dearator typically includes a vertical domed deaeration section as the

deaeration boiler feed water tank. A Steam generating boiler requires that the circulating

steam, condensate, and feed water should be devoid of dissolved gases, particularly

corrosive ones and dissolved or suspended solids. The gases will give rise to corrosion of

the metal. The solids will deposit on the heating surfaces giving rise to localized heating

and tube ruptures due to overheating. Under some conditions it may give rise to stress

corrosion cracking. Deaerator level and pressure must be controlled by adjusting control

valves the level by regulating condensate flow and the pressure by regulating steam flow.

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If operated properly, most deaerator vendors will guarantee that oxygen in the deaerated

water will not exceed 7 ppb by weight (0.005 cm3/L)

3.4.13 FEED WATER HEATER

A Feed water heater is a power plant component used to pre-heat water delivered to a

steam generating boiler. Preheating the feed water reduces the irreversibility involved in

steam generation and therefore improves the thermodynamic efficiency of the system.

This reduces plant operating costs and also helps to avoid thermal shock to the boiler

metal when the feed water is introduced back into the steam cycle. In a steam power

(usually modelled as a modified Rankin cycle), feed water heaters allow the feed water to

be brought up to the saturation temperature very gradually. This minimizes the inevitable

irreversibility associated with heat transfer to the working fluid (water).

3.4.14 COAL CONVEYOR

Coal conveyors are belts which are used to transfer coal from its storage place to Coal

Hopper. A belt conveyor consists of two pulleys, with a continuous loop of material- the

conveyor Belt that rotates about them. The pulleys are powered, moving the belt and

the material on the belt forward. Conveyor belts are extensively used to transport

industrial and agricultural material, such as grain, coal, ores etc.

3.4.15 COAL HOPPER

Coal Hoppers are the places which are used to feed coal to Fuel Mill. It also has the

arrangement of entering Hot Air at 200C inside it which solves our two purposes:-

1. If our Coal has moisture content then it dries it so that a proper combustion takes place.

2. It raises the temperature of coal so that its temperature is more near to its Ignite

Temperature so that combustion is easy.

3.4.16 PULVERIZED FUEL MILL

A pulveriser is a device for grinding coal for combustion in a furnace in a fossil fuel

power plant.

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3.4.17 BOILER DRUM

Steam Drums are a regular feature of water tube boilers. It is reservoir of water/steam at

the top end of the water tubes in the water-tube boiler. They store the steam generated in

the water tubes and act as a phase separator for the steam/water mixture. The difference

in densities between hot and cold water helps in the accumulation of the hotter -

water/and saturated steam into steam drum. Made from high-grade steel (probably

stainless) and its working involve temperature of 390C and pressure well above 350psi

(2.4MPa). The separated steam is drawn out from the top section of the drum. Saturated

steam is drawn off the top of the drum. The steam will re-enter the furnace in through a

super heater, while the saturated water at the bottom of steam drum flows down to the

mud-drum /feed water drum by down comer tubes accessories include a safety valve,

water level indicator and fuse plug.

3.4.18 ASH HOPPER

A steam drum is used in the company of a mud-drum/feed water drum which is located at

a lower level. So that it acts as a sump for the sludge or sediments which have a tendency

to accumulate at the bottom.

3.4.19 SUPER HEATER

A Super heater is a device in a steam engine that heats the steam generated by the boiler

again increasing its thermal energy. Super heaters increase the efficiency of the steam

engine, and were widely adopted. Steam which has been superheated is logically known

as superheated steam; non- superheated steam is called saturated steam or wet steam.

Super heaters were applied to steam locomotives in quantity from the early 20th century,

to most steam vehicles, and also stationary steam engines including power stations.

3.4.20 FORCE DRAUGHT FAN

External fans are provided to give sufficient air for combustion. The forced draught fan

takes air from the atmosphere and, warms it in the air preheater for better combustion,

injects it via the air nozzles on the furnace wall.

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3.4.21 REHEATER

Reheater is a heater which is used to raise the temperature of steam which has fallen from

the intermediate pressure turbine.

3.4.22 AIR INTAKE

Air is taken from the environment by an air intake tower which is fed to the fuel.

3.4.23 ECONOMIZERS

Economizer, or in the UK economizer, are mechanical devices intended to reduce energy

consumption, or to perform another useful function like preheating a fluid. The term

economizer is used for other purposes as well-Boiler, power plant, heating, ventilating

and air-conditioning. In boilers, economizer are heat exchange devices that heat fluids ,

usually water, up to but not normally beyond the boiling point of the fluid. Economizers

are so named because they can make use of the enthalpy and improving the boilers

efficiency. They are devices fitted to a boiler which save energy by using the exhaust

gases from the boiler to preheat the cold water used to fill it (the feed water). Modern day

boilers, such as those in cold fired power stations, are still fitted with economizer which

is decedents of Greens original design. In this context there are turbines before it is

pumped to the boilers. A common application of economizer in steam power plants is to

capture the waste heat from boiler stack gases (flue gas) and transfer thus it to the boiler

feed water thus lowering the needed energy input , in turn reducing the firing rates to

accomplish the rated boiler output . Economizer lower stack temperatures which may

cause condensation of acidic combustion gases and serious equipment corrosion damage

if care is not taken in their design and material selection.

3.4.24 AIR PREHEATER

Air preheater is a general term to describe any device designed to heat air before another

process (for example, combustion in a boiler). The purpose of the air preheater is to

recover the heat from the boiler flue gas which increases the thermal efficiency of the

boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases

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are also sent to the flue gas stack (or chimney) at a lower temperature allowing simplified

design of the ducting and the flue gas stack. It also allows control over the temperature of

gases leaving the stack.

3.4.25 PRECIPITATOR

An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device that

removes particles from a flowing gas (such as air) using the force of an induced

electrostatic charge. Electrostatic precipitators are highly efficient filtration devices, and

can easily remove fine particulate matter such as dust and smoke from the air steam.

ESPs continue to be excellent devices for control of many industrial particulate

emissions, including smoke from electricity-generating utilities (coal and oil fired), salt

cake collection from black liquor boilers in pump mills, and catalyst collection from

fluidized bed catalytic crackers from several hundred thousand ACFM in the largest coal-

fired boiler applications. The original parallel plate-Weighted wire design (described

above) has evolved as more efficient (and robust) discharge electrode designs, today

focus is on rigid discharge electrodes to which many sharpened spikes are attached ,

maximizing corona production. Transformer rectifier systems apply voltages of 50-100

Kilovolts at relatively high current densities. Modern controls minimize sparking and

prevent arcing, avoiding damage to the components. Automatic rapping systems andhopper evacuation systems remove the collected particulate matter while on line allowing

ESPs to stay in operation for years at a time.

3.4.26 INDUCED DRAUGHT FAN

The induced draft fan assists the FD fan by drawing out combustible gases from the

furnace, maintaining a slightly negative pressure in the furnace to avoid backfiring

through any opening. At the furnace outlet and before the furnace gases are handled by

the ID fan, fine dust carried by the outlet gases is removed to avoid atmospheric

pollution. This is an environmental limitation prescribed by law, which additionally

minimizes erosion of the ID fan.

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3.4.27 FLUE GAS STACK

A Flue gas stack is a type of chimney, a vertical pipe, channel or similar structure through

which combustion product gases called flue gases are exhausted to the outside air. Flue

gases are produced when coal, oil, natural gas, wood or any other large combustion 31

device. Flue gas is usually composed of carbon dioxide (CO2) and water vapour as well

as nitrogen and excess oxygen remaining from the intake combustion air. It also contains

a small percentage of pollutants such as particulates matter, carbon mono oxide, nitrogen

oxides and sulphur oxides. The flue gas stacks are often quite tall, up to 400 meters (1300

feet) or more, so as to disperse the exhaust pollutants over a greater area and thereby

reduce the concentration of the pollutants to the levels required by government's

environmental policies and regulations. The flue gases are exhausted from stoves, ovens,

fireplaces or other small sources within residential abodes, restaurants, hotels through

other stacks which are referred to as chimneys.

3.5 VARIOUS CYCLES AT POWER STATION

3.5.1 PRIMARY AIR CYCLE

Fig. 3.5 PRIMARY AIR CYCLE

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3.5.2 SECONDARY AIR CYCLE

Fig. 3.6 SECONDARY AIR CYCLE

3.5.3 ELECTRICITY CYCLE

Fig. 3.7 ELECTRICITY CYCLE

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3.5.4 CONDENSATE CYCLE

Fig. 3.8 CONDENSATE CYCLE

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3.5.5 FEED WATER CYCLE

Fig. 3.9 FEED WATER CYCLE

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3.5.6 STEAM CYCLE

Fig. 3.10 STEM CYCLE

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3.5.7 COAL CYCLE

Fig. 3.11 COAL CYCLE

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3.5.8 FLUE GAS CYCLE

3.12 FLUE GAS CYCLE

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CHAPTER-4

ELECTRICAL MAINTENANCE DEPARTMENT I

4.1MOTORSMotors can be classified as AC and DC.

4.1.1 AC MOTORS

1. Squirrel cage motor

2. Wound motor

3. Slip ring induction

motor In modern thermal power plant three phase squirrel cage induction motors are used

but sometime double wound motor is used when we need high starting torque e.g. in ball

mill.

4.1.2 THREE PHASE INDUCTION MOTOR

Ns (speed) =120f/p

Stator can handle concentrated single layer winding, with each coil occupying one stator

slot

The most common type of winding are:

DISTRIBUTED WINDING: This type of winding is distributed over a number

of slots.

DOUBLE LAYER WINDING: Each stator slot contains sides of two different

coils.

SQUIRREL CAGE INDUCTION MOTOR: Squirrel cage and wound cage

have same mode of operation. Rotor conductors cut the rotating stator magnetic

field. an emf is induced across the rotor winding, current flows, a rotor magnetic

field is produced which interacts with the stator field causing a turning motion.

The rotor does not rotate at synchronous speed, its speed varies with applied load.

The slip speed being just enough to enable sufficient induced rotor current to

produce the power dissipated by the motor load and motor losses motion. The

rotor does not rotate at synchronous speed, its speed varies with applied load.

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The slip speed being just enough to enable sufficient induced rotor current to

produce the power dissipated by the motor load and motor losses.

4.1.3 BEARINGS AND LUBRICATIONS

A good bearing is needed for trouble free operation of motor. Since it is very costly part

of the motor, due care has to be taken by checking it at regular intervals. So lubricating

plays an important role.

Two types of lubricating are widely used

1. Oil lubrication

2. Grease lubrication

3. Insulation

4.1.4 INSULATION

Winding is an essential part so it should be insulated. Following types of insulation are

widely used

TYPES OF INSULATION

CLASS TEMP UPTO WHICH THEY ARE

EFFECTIVE (DEGREE CENTIGRADE)

Y 90

A 105

E 120

B 130

F 150

H 180

C More than 180

Table 4.1 TYPE OF INSULATORS

F class insulation is generally preferred.

4.1.5 MAIN MOTOR USED IN BOILER AND OFF SIDE AREA

1. ID FAN( 2 PER UNIT)

It is located between EP and chimney used for creating induced draft in the

furnace.

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2. PA FAN(2 PER UNIT)

It is used for handling atmospheric air up to temperature 50 degree centigrade

3. FD FAN(2 PER UNIT)

It is used for handling secondary air for the boiler.

4. SCANNER FAN( 2 PER UNIT )

It is required for requisite air for scanner cooling.

5. IGNITOR FAN

It supplies air for cooling of igniters.

4.1.6 INSTRUMENTS SEEN

1. MICROMETER

This instrument is used for measuring inside as well as outside diameter of

bearing.

2. MEGGAR

This instrument is used for measuring insulation resistance.

3. VIBRATION TESTER

It measures the vibration of the motor. It is measured in three dimensions-axial,

vertical and horizontal.

4.2 SWITCHGEAR

4.2.1 INTRODUCTION

Switchgear is one that makes or breaks the electrical circuit. It is a switching device that

opens& closes a circuit that defined as apparatus used for switching, Lon rolling &

protecting the electrical circuit & equipments. The switchgear equipment is essentially

concerned with switching & interrupting currents either under normal or abnormal

operating conditions. The tubular switch with ordinary fuse is simplest form of

switchgear & is used to control & protect& other equipments in homes, offices etc. For

circuits of higher ratings, a High Rupturing Capacity (H.R.C) fuse in condition with a

switch may serve the purpose of controlling &protecting the circuit. However such

switchgear cannot be used profitably on high voltage system (3.3 KV) for 2 reasons.

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Firstly, when a fuse blows, it takes some time to replace it &consequently there is

interruption of service to customer. Secondly, the fuse cannot successfully interrupt large

currents that result from the High Voltage System. In order to interrupt heavy fault

currents, automatic circuit breakers are used. There are very few types of circuit breakers

in B.P.T.S they are VCB, OCB, and SF6 gas circuit breaker. The most expensive circuit

breaker is the SF6 type due to gas. There are various companies which manufacture these

circuit breakers: VOLTAS, JYOTI, and KIRLOSKAR. Switchgear includes switches,

fuses, circuit breakers, relays & other equipments.

4.2.2 EQUIPMENTS:-

ISOLATOR: An isolator is one that can break the electrical circuit when the

circuit is to be switched on no load. These are used in various circuits for isolating

the certain portion when required for maintenance etc. An operating mechanism

box normally installed at ground level drives the isolator. The box has an

operating mechanism in addition to its contactor circuit and auxiliary contacts

may be solenoid operated pneumatic three phase motor or DC motor transmitting

through a spur gear to the torsion shaft of the isolator. Certain interlocks are also

provided with the isolator

These are1. Isolator cannot operate unless breaker is open

2. Bus 1 and bus 2 isolators cannot be closed simultaneously

3. The interlock can be bypass in the event of closing of bus coupler breaker.

4. No isolator can operate when the corresponding earth switch is on

SWITCHING ISOLATOR

Switching isolator is capable of:1. Interrupting charging current

Interrupting transformer magnetizing current

Load transformer switching. Its main application is in connection with the

transformer feeder as the unit makes it possible to switch gear one transformer

while the other is still on load.

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CONTACTORS: AC Contractors are 3 poles suitable for D.O.L Starting of

motors and protecting the connected motors.

Fig. 4.1 CONTACTOR

OVERLOAD RELAY: For overload protection, thermal overload relay are best

suited for this purpose. They operate due to the action of heat generated by

passage of current through relay element.

Fig. 4.2 OVERLOAD RELAY

AIR CIRCUIT BREAKERS: It is seen that use of oil in circuit breaker may

cause a fire. So in all circuits breakers at large capacity air at high pressure is used

which is maximum at the time of quick tripping of contacts.

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This reduces the possibility of sparking. The pressure may vary from 50-

60kg/cm^2 for high and medium capacity circuit breakers.

4.2.4 HT SWITCHGEAR

MINIMUM OIL CIRCUIT BREAKER: These use oil as quenching medium. It

comprises of simple dead tank row pursuing projection from it. The moving

contracts are carried on an iron arm lifted by a long insulating tension rod and are

closed simultaneously pneumatic operating mechanism by means of tensions but

throw off spring to be provided at mouth of the control the main current within

the controlled device.

Fig. 4.3 OIL CIRCUIT BREAKER

Type-HKH 12/1000c

Rated Voltage-66 KV

Normal Current-1250A

Frequency-5Hz

Breaking Capacity-3.4+KA Symmetrical

3.4+KA Asymmetrical

360 MVA Symmetrical

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Motor Voltage-220 V/DC

AIR CIRCUIT BREAKER

Fig. 4.4 AIR CIRCUIT BREAKER

In this the compressed air pressure around 15 kg per cm^2 is used for extinction

of arc caused by flow of air around the moving circuit. The breaker is closed by

applying pressure at lower opening and opened by applying pressure at upper

opening. When contacts operate, the cold air rushes around the movable contacts

and blown the arc: It has the following advantages over OCB:-

i. Fire hazard due to oil are eliminated.

ii. Operation takes place quickly.

iii. There is less burning of contacts since the duration is short and consistent.

iv. Facility for frequent operation since the cooling medium is replaced

constantly.

Rated Voltage-6.6 KV

Current-630 A

Auxiliary current-220 V/DC

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SF6 CIRCUIT BREAKER

Fig. 4.5 SF6 CIRCUIT BREAKER

This type of circuit breaker is of construction to dead tank bulk oil to circuit

breaker but the principle of current interruption is similar to that of air blast circuit

breaker. It simply employs the arc extinguishing medium namely SF6. When it is

broken down under an electrical stress, it will quickly reconstitute itself.

Circuit Breakers-HPA

Standard-1 EC 56

Rated Voltage-12 KV

Insulation Level-28/75 KV

Rated Frequency-50 Hz

Breaking Current-40 KA

Rated Current-1600 A

Making Capacity-110 KA

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VACUUM CIRCUIT BREAKER: It works on the principle that vacuum is used

to save the purpose of insulation and. In regards of insulation and strength,

vacuum is superior dielectric medium and is better that all other medium except

air and sulphur which are generally used at high pressure.

Rated frequency-50 Hz

Rated making Current-10 Peak KA

Rated Voltage-12 KV

Supply Voltage Closing-220 V/DC

4.3 COAL HANDLING PLANT

4.3.1 INTRODUCTION

The coal handling plant consists of two plants:

Old Coal Handling Plant (OCHP)

New Coal Handling Plant (NCHP)

The OCHP supplies coal to Unit- I, II, III &

NCHP supplies coal to Unit- IV and V.

4.3.2 COAL SUPPLIED AT BTPS

Coal is supplied to BTPS by Jharia coal mines. It is non-cooking coal and has following

specifications:-

Moisture- less than 8%

Volatile matter-17% to 19%

Ash- 35% - 40%

Calorific Value- 4500 to 5300 Kcal/kg

Coal is received in railway box racks containing 20 - 42 wagons in each rack.

Capacity of each box wagon is about 55 ton.

These wagons are placed on 2 wagon tippler in OCHP & one wagon tippler in

NCHP, in total 3, capacity 80 ton each.

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Fig. 4.6 COAL PLANT

4.3.3 OLD COAL HANDLING PLANT

Fig. 4.7 OLD COAL HANDLING PLANT

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The main constituents of OCHP plant are:-

WAGON TIPPLER :Wagon from coal yard come to the tippler and emptied

here. There are 2 wagon tipplers in the OCHP. The tippler is tilted to about 137-

141 so that coal from the wagon is emptied into the hopper. Elliptic feeder is

used in OCHP. Total 8 feeders are used, 4 in each hopper.

Slip Ring Induction Motor is used to operate a wagon tippler. This type of IM is

used in the tippler because of its high resistance, low speed & high torque

characteristics. The rating of the motor used is:

Power 55 KW

Voltage 415V

Current 102A

Speed 1480rpm

Phase 3

Frequency 50Hz

Three types of wagon tipplers are used:-

a) ROTASIDE: -

It is used for open type wagons in which each wagon carries around 50- 56 tons

of coal. The wagon is tilted by 150 to put the coal in the unloading hopper.

b) ROTARY: -

In this case the unloading hopper is placed directly under the tippler table. This is

also used to tilt the wagon tippler to 180.

c) ROCKING TYPE: -

It is used for close type wagons. In this hoppers is placed by the side of end

rocking is provided to facilitate unloading of coal at corners of the wagon.

CONVEYER: Conveyer belts are used in the OCHP to transfer coal from one

place to other as required in a convenient & safe way. All the belts are numbered

accordingly so that their function can be easily demarcated. These belts are made

of rubber & move with a speed of 250-300 m/min. Motor employed for the

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conveyer has a capacity of 150 HP. These conveyers have a capacity of carrying

the coal at the rate of 400 ton/hr.

ZERO SPEED SWITCH: It is used as a safety device for the motor i.e. if the

belt is not moving & the motor is ON, then it burns to save the motor. This switch

checks the speed of the belt & switches off the motor when speed is zero.

METAL DETECTOR: As the conveyer belt take coal from wagon to crusher

house, no metal piece should go along with coal. To achieve this objective, metal

detectors & separators are used. In the OCHP, these MDs are installed in the

conveyer belts 2A & 2B.

CRUSHER HOUSE: Both the plants i.e. OCHP & NCHP use TATA crusher

powered by BHEL motor. Crusher is of ring type and the motor is a HT motor of

rating 400HP & 6.6 KV. Crusher is designed to crush the pieces to 20 mm size i.e.

practically considered as the optimum size for transfer via conveyer.

ROTARY BREAKER: If any large piece of metal of any hard substances like

metal impurities comes in the conveyer belt which cause load on the metal

separator, then the rotary breaker rejects them reducing the load on the metal

detector.

STACKER-CUM-RECLAIMER: It is used for stacking & reclaiming the coal

from the stockyard in case of unavailability of wagons from coal mines.

PLOUGH FEEDER: These plough feeders are generally installed under slot

bunkers or hoppers. These are used top laugh the coal to the belt from the coal fed

from stockyard. These feeders used in this power station are generally of rotary

type.

TRIPPERS: Trippers are provided in the conveyer to collect the material at

desired location on either side or along the conveyer with the help of chute/ducts

fitted with tripper itself. The motor in the tripper can make it move both in

forward and reverse direction.

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PULL GUARD SWITCH: These are the switches which are installed at every

10m gap in a conveyer belt to ensure the safety of motors running the conveyer

belts. If at any time some accident happens or coal jumps from belt and starts

collecting at a place, this switch can be moved to NO(normally open) position

from NC (normally closed) position to stop conveyor belt from moving. At this

time the problem can be corrected & then again the switch can be moved to NC

(normally closed) position for normal working again.

INTERLOCKS: - The CHP is normally spread over a wide area with centralized

control room. Elaborate scheme is therefore provided. If due to any emergency

either the conveyor belt or the motor has to be stopped, due to this interlocking allthe other motors connected to it will automatically stop &will not work till signal

is given from the control room.

The control & protection scheme normally includes: -

A hooter system to warn that the plant is going to be started. The plant can be

started only after a definite time after the hooter is energized.

Sequential starting of conveyor system and tripping of all proceeding system if

any equipment in the chain is tripped.

Tripping of conveyor from speed switch for protection against belt slippage.

4.3.4 SEQUENTIAL OPERATION OF OCHP: -

I. Unloading the coal

II. Crushing & storage.

III. Conveying to boiler bunkers.

a) Coal arrives to plant via road, rail, sea, and river or canal route from

collieries. Most of it arrives by rail route only in railway wagons. Coal

requirement by this plant is approximately 10,500 metric ton/day.

b) This coal is tippled into hoppers. If the coal is oversized (400 mm sq),

then it is broken manually so that it passes the hopper mesh where

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through elliptic feeder it is put into vibrators & then to conveyor belt 1A

& 1B

c) The coal through conveyor belts 1A & 1B goes to the crusher house. Also

the extra coal is sent to stockyard through these belts.

d) In the crusher house the small size coal pieces goes directly to the belt 2A

& 2B whereas the big size coal pieces are crushed in the crusher & then

given to the belts 2A & 2B.

e) The crushed coal is taken to the bunker house via the conveyor belts 3A

& 3B where it can be used for further operations.

4.4 NEW COAL HNDLING PLANT

Fig. 4.8 NEW COAL HANDLING PLANT

The main constituents of NCHP plant are:-

Most of the constituents of the NCHP are the same as that of OCHP.

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4.4.1 WAGON TIPPLER

In NCHP there is only one wagon tippler. In this it takes 52 sec to raise a wagon, 10 sec

to empty the wagon completely & then again 52 sec to bring the tippler down. A

semicircular huge WT gear is used to run the tippler. Protocol cameras have been

installed for safety to ensure that no moving creature or object is near the wagon which is

on the tippler.

Fig. 4.9 WAGON TIPPLER

4.4.2 COAL FEEDER TO THE PLANT

Vibro feeders are installed below the hopper which helps in putting the coal to the

conveyor belts. There are 2 conveyor belts & 3 vibro feeder per plant, so in total there are

6 vibrofeeders.

Given below are the feeder motor specifications:

Power 15HP

Voltage 415V

Speed 1450rpm

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4.4.3 CONVEYOR TURNING POINT-6BREAKER HOUSE

This house is required to render the coal size to 100mm sq. A 415W LT motor is used in

the breaker house.

4.4.4 REJECTION HOUSE

The coal comes to breaker house via conveyor belts 12A & 12B. Now in the breaker

house the huge stones & metal impurities are separated & sent to reject bin house through

belts 18A &18B.

4.4.5 RECLAIM HOPPER

It is the stockyard in which coal is stored for emergency purposes. Around 3 lakh ton of

coal can be stored in it.

4.4.6 TURNING POINT 7 CRUSHER HOUSE

To ensure that the coal is of uniform size it is passed through crusher. The crusher is of

ring type. Has a motor rating of 400HP, 606KV. It is designed to crush the pieces to

20mm size

4.4.7SEQUENTIAL OPERATION OF NCHP:-

a) Coal arrives in wagons and tipples into hoppers.

b) if the coal is oversized (400mm sq), then it is broken manually so that it passes

through the hopper mesh.

c) From hopper it is taken to TP-6 12A & 12B. d) Conveyors 12A & 12B take the

coal to the breaker house which renders the coal size to be 100 mm sq.

d) Metal separator & metal detector are installed in conveyor belts 14A/B & 15A/B

respectively to remove the metal impurities.

e) Stones which are not able to pass through the 100mm sq mesh of hammer are

rejected via 18A & 18B to the rejection house.

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f) Extra coal is sent to the reclaim hopper via conveyor 16A & 16B. h)From TP-7,

coal is taken by conveyor 14A & 14B to the crusher house whose function is to

render size of the coal to 20mm sq.

4.5 SPECIFICATIONS OF MOTORS USED IN NCHP:-

I. Crusher: - BHEL ILAT/12B HD/02, 736rpm, 550Kw, 6600V.

II. Wagon Tippler: - 5D315l, 98Kw slip ring motor.

III. Conveyors: -

1)11A/B, 12A/B: - 125Kw, 315m, 1485rpm.

2)13A/B: - 55Kw, 250m, 1480rpm.

3)14A/B, 15A/B: - 150Kw, 355m, 1485rpm.

4)16A/B, 17A/B: - 110Kw, 315m, 1485rpm.

5)18A/B: - 37Kw, 225m, 1470rpm.

IV. Rotary Breaker: - 110Kw, 315m, 1485rpm

V. Belt Feeder: - 15Kw, 180L, 1445rpm

VI. Reversible Belt Feeder: - 18.7Kw, 200L, 1485rp

VII. VF 1-6: - 7.5Kw, 160m, 1485rpm

VIII. VF 7-8: - 15Kw, 180L, 1485rpm

IX.

VF 9-12: - 11Kw,160L, 1485rpm

X. WSP Crusher House: - 15Kw, 160m, 4000rpm

XI. WSP Breaker House: - 7.5Kw, 132m, 1865rpm

XII. Metal Separator: - 5KV, 132m, 1410rpm

XIII. Spray Precipitator: - 18.5Kw, 200L, 3000rpm

4.5.1 SAFETY DEVICES FOR BELT CONVEYORS

Sometimes the belt is wet due to any reason, so it may not run due to reduced friction. Aswitch senses this and prevents the belt from choking. Sometime any accident may occur

which requires the belt to stop, the pull cords are pulled to stop the conveyor. This system

starts again only when the pull cords are rest. There is a push button in the control room

from where the belt can be stopped in case of emergency stoppage.

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Other equipments are pulley. Pulleys are made of mild steel, rubber logging is provided

to increase the friction factor between the pulley and belt .

4.6 MILLING SYSTEM

RC BUNKER: Raw coal is fed directly to these bunkers. These are 3 in no. per

boiler. 4 & tons of coal are fed in 1 hr. the depth of bunkers is 10m.

RC FEEDER: It transports pre-crust coal from raw coal bunker to mill. The

quantity of raw coal fed in mill can be controlled by speed control of aviator drive

controlling damper and aviator change

BALL MILL: The ball mill crushes the raw coal to a certain height and then

allows it to fall down. Due to impact of ball on coal and attraction as per the

particles move over each other as well as over the Armor lines, the coal gets

crushed. Large particles are broken by impact and full grinding is done by

attraction. The Drying and grinding option takes place simultaneously inside the

mill. In ball mill coal is converted to powdered form and due to pneumatic action

the powdered form of coal is transferred upwards.

CLASSIFIER: It is equipment which serves separation of fine pulverized coal

particles medium from coarse medium. The pulverized coal along with the

carrying medium strikes the impact plate through the lower part. Large particles

are then transferred to the ball mill.

MILL FAN: From ball mill the powdered coal is sucked through mill fan

CYCLONE SEPARATORS: It separates the pulverized coal from carrying

medium. The mixture of pulverized coal vapour caters the cyclone separatorstangentially in the upper part of the separator. Due to decrease in the velocity the

centrifugal action, the pulverized coal separated from the vapour &falls down to

the lower epical part.

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THE TURNIGATE: It serves to transport pulverized coal from cyclone

separators to pulverized coal bunker or to worm conveyors. There are 4 turnigates

per boiler.

WORM CONVEYOR: It is equipment used to distribute the pulverized coal

from bunker of one system to bunker of other system. It can be operated in both

directions.

4.10 WORM CONVEYOR

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CHAPTER-5

ELECTRICAL MAINTENANCE DEPARTMENT II

5.1GENERATOR

5.1.1 INTRODUCTION

Fig. 5.1 GENERATOR

There are two components:

1. Stator

2. Rotor.

The rotor is the moving part and the stator is the stationary part. The rotor, which has

a field winding, is given a excitation through a set of 3000rpm to give the required

frequency of HZ. The rotor is cooled by Hydrogen gas, which is locally manufactured

by the plant and has high heat carrying capacity of low density. If oxygen and

hydrogen get mixed then they will form very high explosive and to prevent their

combining in any way there is seal oil system. The stator cooling is done by de-

mineralized (DM) water through hollow conductors. Water is fed by one end by

Teflon tube. A boiler and a turbine are coupled to electric generators. Steam from the

boiler is fed to the turbine through the connecting pipe. Steam drives the turbine rotor.

The turbine rotor drives the generator rotor which turns the electromagnet within the

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coil of wire conductors. Carbon dioxide is provided from the top and oil is provided

from bottom to the generator. With the help of carbon dioxide the oil is drained out to

the oil tank.

Hydrogen gas is used to cool down the rotor.

Lube oil is used to cool the bearings.

DM water is used to cool the stator.

Seal oil is used to prevent hydrogen leakage

Seal oil coolers are present to cool the seal oil

Hydrogen dryer are used which removes the moisture from hydrogen gas and

then is supplied to the generator.

Clarified water in cooling tower is used to cool down the hydrogen gas.

5.1.2 RATINGS OF THE GENERATORS USED

Two types of generator used

Turbo generator 100MW

Turbo generator 210 MW

The 100 MW generator generates 10.75 KV and 210 MW generates 15.75 KV. The

voltage is stepped up to 220 KV with the help of generator transformer and is connected

to the grid.

The voltage is stepped down to 6.6 KV with the help of UNIT AUXILLARY

TRANSFORMER (UAT) and this voltage is used to drive the HT motors. The voltage is

further stepped down to 415 V and then to 220 V and this voltage is used to drive Lt

Motors.

5.1.3 BASIC PRINCIPLE

The generator works on the principle of electromagnetic induction.

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5.1.3 TURBO GENERATOR 100MW

MAKEBHEL, Haridwar

CAPACITY 117,500 KVA

POWER 100,000 KW

STATOR VOLTAGE 10,500 V

STATOR CURRENT 6475 A

SPEED 5000rpm

POWER FACTOR 0.85

FREQUENCY 50 HZ

EXCITATION 280 V

Table 5.1 GENERATOR 100MW

5.1.4 TURBO GENERATOR 210MW

MAKEBHEL, Haridwar

CAPACITY 247,000 KVA

POWER 210,000 KW

STATOR VOLTAGE 15,750 V

STATOR CURRENT 9050 A

SPEED 5000 rpm

POWER FACTOR 0.85

FREQUENCY 50 HZ

EXCITATION 310 V

GAS PRESSURE 5.2 kg/cm

Table 5.2 GENERATOR 210M

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5.2 TRANSFORMERS

5.2.1 INTRODUCTION

Fig. 5.2 TRANSFORMER

It is a static machine which increases or decreases the AC voltage without changing the

frequency of the supply.

It is a device that: Transfer electric power from one circuit to another.

It accomplishes this by electromagnetic induction.

In this the two electric circuits are in mutual inductive influence of each other

5.2.2 WORKING PRINCIPLE:

It works on FARADAYS LAW OF ELECTROMAGNETIC INDUCTION (self or

mutual induction depending on the type of transformer).

5.2.3 MAIN PARTS

CONSERVATOR: It is used generally to conserve the insulating property of the

oil from deterioration& protect the transformer against failure on account of bad

quality of oil.

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SILICAGEL DEHYDRATING BREATHER: It is used to prevent entry of

moisture inside the transformer tank. The breather consists of silica gel.

GAS OPERATED RELAY (BUCHHOLZ RELAY): It is a gas actuated relay

used for protecting oil immersed transformer against all types of faults. It

indicates presence of gases in case of some minor fault & take out the transformer

out of circuit in case of serious fault.

BUSHINGS: It is made from highly insulating material to insulate & to bring out

the terminals of the transformer from the container. The bushings are of 3 types:

a. Porcelain bushings used for low voltage transformer b. Oil filled bushings used

for voltage up to 33KV. c. Condensed type bushings used for voltage above

33KV.

OIL GUAGE: Every transformer with an oil guage to indicate the oil level. The

oil guage may be provided with the alarm contacts which gave an alarm the oil

level has dropped beyond permissible height due to oil leak etc.

TAPPINGS: The transformers are usually provided with few tappings on

secondary side so that output voltage can be varied for constant input voltage.

RADIATORS: It increases the surface area of the tank & more heat is thus

radiated in less time.

WINDINGS TEMPERATURE INDICATOR (OIL GUAGE): Device which

indicates the temperature of winding of transformer & possible damage to the

transformer due too overload can be prevented.

5.2.4 CONSTRUCTIONAL FEATURES:

3 phase transformer is constructed in the core type construction.

For reducing losses a smaller thickness of lamination is used.

For the above reason it is also called cold-rolled steel instead hot-rolled steel is

used.

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High flux densities (1.4 to 1.7 Wb/sq m) are used in the core of power

transformer which carry load throughout.

For high voltage winding, disc type coils are used.

5.2.5 CLASSIFICATION:

ACCORDING TO THE CORE:

a) Core type transformer

b) Shell type transformer

c) Berry type transformer

ACCORDING TO PHASES:

a) 1phase transformer

b) 3phase transformer

ACCORDING TO THE PURPOSE FOR WHICH USED :

a) Distribution transformer

b) Transmission transformer

c) Generator transformer

d) Station transformer

e) Unit Auxiliary transformer (UAT)

5.2.6 COOLING OF TRANSFORMERS OF LARGE MVA:

As size of transformer becomes large, the rate of the oil circulating becomes insufficient

to dissipate all the heat produced & artificial means of increasing the circulation by

electric pumps. In very large transformers, special coolers with water circulation may

have to be employed.

TYPES OF COOLING:

AIR COOLING

1. Air Natural (AN)

2. Air Forced (AF)

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OIL IMMERSED COOLING

1. Oil Natural Air Natural (ONAN)

2. Oil Natural Air Forced (ONAF)

3. Oil Forced Air Natural (OFAN)

4. Oil Forced Air Forced (OFAF)

OIL IMMERSED WATER COOLING

1. Oil Natural Water Forced (ONWF)

2. Oil Forced Water Forced (OFWF)

5.2.7 MAIN PARTS OF TRANSFORMER

i. Secondary Winding

ii. Primary Winding.

iii. Oil Level

iv. Conservator

v. Breather

vi. Drain Cock

vii. Cooling Tubes.

viii.

Transformer Oil.

ix. Earth Point

x. Explosion Vent

xi. Temperature Gauge.

xii. Buchholz Relay

xiii. Secondary Terminal

xiv. Primary Terminal

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5.2.8GENERATOR TRANSFORMER (125MVA UNIT-I & UNIT-III)

RATING 125MVA

TYPE OF COOLING OFB

TEMP OF OIL 45^C

TEMP WINDING 60^C

KV (no load) HV-233 KVA

LV-10.5 KVA

LINE AMPERES HV-310 A

LV-6880

PHASE THREE

FREQUENCY 50 HZ

IMPEDANCE VOLTAGE 15%

VECTOR GROUP Y DELTA

INSULATION LEVEL HV-900 KV

LV-Neutral-38

CORE AND WINDING

WEIGHT

110500 Kg

WEIGHT OF OIL 37200 Kg

TOTAL WEIGHT 188500 Kg

OIL QUANTITY 43900 lit

Table 5.3 TRANSFORMER 125MVA

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5.2.9 GENERATOR TRANSFORMER (166 MVA UNIT-IV)

RATING 250MVA

TYPE OF COOLING On/OB/OFB

TEMP OF OIL 45^C

TEMP WINDING 60^C

VOLTS AT NO LOAD HV-236000

LV-15750

LINE AMPERES HV-587 A

LV-8798

PHASE THREE

FREQUENCY 50 HZ

IMPEDANCE VOLTAGE 15.55%

VECTOR GROUP Y DELTA

CORE AND WINDING WEIGHT 138800 Kg

WEIGHT OF OIL 37850 Kg

TOTAL WEIGHT 234000 Kg

OIL QUANTITY 429500 lit

GUARANTEED MAX TEMP 45^C

DIVISION KERELA

YEAR 1977

Table 5.4 TRANSFORMER 165MVA

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5.2.10 UNIT AUXILIARY TRANSFORMER (UAT)

Unit I & V- 12.5 MVA

The UAT draws its input from the main bus-ducts. The total KVA capacity of UAT

required can be determined by assuming 0.85 power factor & 90% efficiency for total

auxiliary motor load. It is safe & desirable to provide about 20% excess capacity then

circulated to provide for miscellaneous auxiliaries & possible increase in auxiliary.

5.2.11 STATION TRANSFORMER

It is required to feed power to the auxiliaries during start-ups. This transformer is

normally rated for initial auxiliary load requirements of the unit in typical cases; this load

is of the order of 60% of the load at full generating capacity. It is provided with on load

tap change to cater to the fluctuating voltage of the grid.

5.2.12NEUTRAL GROUNDED TRANSFORMER

This transformer is connected with supply coming out of UAT in stage-2. This is used to

ground the excess voltage if occurs in the secondary of UAT in spite of rated voltage.

5.3 SWITCH YARD

5.3.1 INTRODUCTION

As we know that electrical energy cant be stored like cells, so what we generate should

be consumed instantaneously. But as the load is not constants therefore we generate

electricity according to need i.e. the generation depends upon load. The yard is the places

from where the electricity is send outside. It has both outdoor and indoor equipments.

5.3.2 OUTDOOR EQUIPMENTS

BUS BAR: Bus bars generally are of high conductive aluminum conforming to

IS-5082 or copper of adequate cross section .Bus bar located in air insulated

enclosures & segregated from all other components .Bus bar is preferably cover

with polyurethane.

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BY PASS BUS: This bus is a backup bus which comes handy when any of the

buses become faulty. When any operation bus has fault, this bus is brought into

circuit and then faulty line is removed there by restoring healthy power line.

LIGHTENING ARRESTOR: It saves the transformer and reactor from over

voltage and over currents. It grounds the overload if there is fault on the line and

it prevents the generator transformer. The practice is to install lightening arrestor

at the incoming terminal of the line. We have to use the lightning arrester both in

primary and secondary of transformer and in reactors. A meter is provided which

indicates the surface leakage and internal grading current of arrester.

WAVE TRAP: Power line carrier communication (PLCC) is mainly used for

telecommunication, tele-protection and tele-monitoring between electrical

substations through power lines at high voltages, such as 110 kV, 220 kV, and

400 kV. PLCC integrates the transmission of communication signal and 50/60 Hz

power signal through the same electric power cable. The major benefit is the

union of two important applications in a single system. WAVETRAP is connected

in series with the power (transmission) line. It blocks the high frequency carrier

waves (24 KHz to 500 KHz) and let power waves (50 Hz - 60 Hz) to pass-

through.

BREAKER: Circuit breaker is an arrangement by which we can break the circuit

or flow of current. A circuit breaker in station serves the same purpose as switch

but it has many added and complex features. The basic construction of any circuit

breaker requires the separation of contact in an insulating fluid that servers two

functions:

extinguishes the arc drawn between the contacts when circuit breaker opens.

It provides adequate insulation between the contacts and from each contact to

earth.

.

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CAPACITATIVE VOLTAGE TRANSFORMER: A capacitor voltage

transformer (CVT) is a transformer used in power systems to step-down extra

high voltage signals and provide low voltage signals either for measurement or to

operate a protective relay. It is located in the last in the switchyard as it increases

the ground resistance. Finally the voltage from CVT in the switchyard is sent out

from the station through transmission lines.

EARTHING ROD: Normally un-galvanized mild steel flats are used for

earthling. Separate earthing electrodes are provided to earth the lightening arrestor

whereas the other equipments are earthed by connecting their earth leads to the

rid/ser of the ground mar.

CURRENT TRANSFORMER: It is essentially a step up transformer which step

down the current to a known ratio. It is a type of instrument transformer designed

to provide a current in its secondary winding proportional to the alternating

current flowing in its primary.

POTENTIAL TRANSFORMER: It is essentially a step down transformer and it

step downs the voltage to a known ratio.

5.3.3 INDOOR EQUIPMENTS

RELAYS: Relay is a sensing device that makes your circuit ON or OFF. They

detect the abnormal conditions in the electrical circuits by continuously measuring

the electrical quantities, which are different under normal and faulty conditions,

like current, voltage frequency. Having detected the fault the relay operates to

complete the trip circuit, which results in the opening of the circuit breakers and

disconnect the faulty circuit.

There are different types of relays:

Current relay

Potential relay

Electromagnetic relay

Numerical relay etc.

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AIR BREAK EARTHING SWITCH: The work of this equipment comes into

picture when we want to shut down the supply for maintenance purpose. This help

to neutralize the system from induced voltage from extra high voltage. This

induced power is up to 2KV in case of 400 KV lines.

ELECTROSTATIC PRECIPITATOR: An electrostatic precipitator (ESP) or

electrostatic air cleaner is a particulate collection device that removes particles

from a flowing gas (such as air) using the force of an induced electrostatic charge.

Electrostatic precipitators are highly efficient filtration devices that minimally

impede the flow of gases through the device, and can easily remove fine

particulate matter such as dust and smoke from the air stream. 82 In contrast to

wet scrubbers which apply energy directly to the flowing fluid medium, an ESPapplies energy only to the particulate matter being collected and therefore is very

efficient in its consumption of energy (in the form of electricity). The most basic

precipitator contains a row of thin vertical wires, and followed by a stack of large

flat metal plates oriented vertically, with the plates typically spaced about 1 cm

to18 cm apart, depending on the application. The air or gas stream flows

horizontally through the spaces between the wires, and then passes through the

stack of plates. A negative voltage of several thousand volts is applied between

wire and plate. If the applied voltage is high enough an electric (corona) discharge

ionizes the gas around the electrodes. Negative ions flow to the plates and charge

the gas-flow particles. The ionized particles, following the negative electric field

created by the power supply, move to the grounded plates. Particles build up on

the collection plates and form a layer. The layer does not collapse, thanks to

electrostatic pressure (given from layer resistivity, electric field, and current

flowing in the collected layer).

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CONCLUSION

It was a wonderful experience, training in NATIONAL THERMAL POWER

CORPORATION, Badarpur plant.

There is great scope for engineers in the field of power generation.

Exposure to practical working conditions will be beneficial for our career.

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BIBLIOGRAPHY

National Power Training Institute website.

NTPC.in.

NTPC Limited.

www. Telegraphindia.com.

BSE india.com.

MoneyControl.com.