Trainee Report Ntpc[1]

8/6/2019 Trainee Report Ntpc[1]

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PROJECT REPORT ( N.T.P.C. BADARPUR, NEW DELHI )INDUSTRIAL TRAINING REPORT

(SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRMENT OF THE

COURSE OF B.TECH.)

UNDERTAKEN ATN.T.P.C. BADARPUR, NEW DELHI

FROM:13th JUNE to 23 JULY 2011

SUBMITTED BY:navneet kumarN.T.P.C. Badarpur


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B.Tech 3rd YearElectrical Engineeringjiet jodhpur

Acknowledgement

With profound respect and gratitude, I take the opportunity to convey my thanks to

complete the training here.

I do extend my heartfelt thanks to Mr Manmohan Singh Singh for providing me

this opportunity to be a part of this esteemed organization.

I am extremely grateful to all the technical staff of BTPS/NTPC for their co-

operation and guidance that helped me a lot during the course of training. I have

learnt a lot working under them and I will always be indebted of them for this value

addition in me.

I would also like to thank the HOD of RIMT IET and all the faculty member of

Electrical department for their effort of constant co-operation. Which have beensignificant factor in the accomplishment of my industrial training.


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CONTENT

1. Introduction to the Company

2. Project Report

b. EMD I

i. Electrical Motorii. Switchgear

c. EMD II

i. Generatorii. Protectioniii. Transformer


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Introduction to theCompanyNTPC, the largest power Company in India, was setup in 1975 to accelerate power

development in the country. It is among the worlds largest and most efficient power

generation companies. In Forbes list of Worlds 2000 Largest Companies for the

year 2007, NTPC occupies 411th place.

NTPC has installed capacity of 29,394 MW. It has 15 coal based power stations

(23,395 MW), 7 gas based power stations (3,955 MW) and 4 power stations in Joint

Ventures (1,794 MW). The company has power generating facilities in all major

regions of the country. It plans to be a 75,000 MW company by 2017.

NTPC has gone beyond the thermal power generation. It has diversified into hydro

power, coal mining, power equipment manufacturing, oil & gas exploration, power

trading & distribution. NTPC is now in the entire power value chain and is poised

to become an Integrated Power Major.NTPC's share on 31 Mar 2008 in the total installed capacity of the country was

19.1% and it contributed 28.50% of the total power generation of the country

during 2007-08. NTPC has set

new benchmarks for the power industry both in the area of power plant

construction and

operations.


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In November 2004, NTPC came out with 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 with Government holding 89.5% of the equity share capital and rest held by

Institutional Investors and Public. The issue was a resounding success. NTPC is among the

largest five companies in India in terms of market capitalization.

Recognizing its excellent performance and vast potential, Government of the India has

identified NTPC as one of the jewels of Public Sector 'Navratnas'- a potential global giant.

Inspired by its glorious past and vibrant present, NTPC is well on its way to realize its vision of

being "A world class integrated power major, powering India's growth, with increasing global

presence".


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Environment Management

All stations of NTPC are ISO 14001 certified

Various groups to care of environmental issues

The Environment Management Grou

Ash Utilization Division

Afforestation Group

Centre for Power Efficiency & Environment Protection

Group on Clean Development Mechanism

N TPC is the second largest owner of trees in the country after the Forest department


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THERMAL POWER PLANT

A Thermal Power Station comprises all of the equipment and a

subsystem required to produce electricity by using a steam generating

boiler fired with fossil fuels or befouls to drive an electrical generator.

Some prefer to use the term ENERGY CENTER because such facilities

convert forms of energy, like nuclear energy, gravitational potential

energy or heat energy (derived from the combustion of fuel) into

electrical energy. However, POWER PLANT is the most common term in

the united state; While POWER STATION prevails in many

Commonwealth countries and especially in the United Kingdom.

Such power stations are most usually constructed on a very large scale

and designed for continuous operation.

Typical diagram of a coal fired thermal power station

1. Cooling water pump

2. Three-phase transmission line

3. Step up transformer

4. Electrical Generator

5. Low pressure steam

6. Boiler feed water pump

7. Surface condenser

8. Intermediate pressure steam turbine

9. Steam control valve

10. High pressure steam turbine

11. Deaerator Feed water heater

12. Coal conveyor

13. Coal hopper

14. Coal pulverizer

15. boiler steam drum

16. Bottom ash hoper

17. Super heater

18. Forced draught(draft) fan

19. Reheater

20. Combustion air intake

21. Economizer

22. Air preheater

23. Precipitator


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24. Induced draught(draft) fan

25. Fuel gas stack

The description of some of the components written above is described

as follows:

1. Cooling towers

Cooling Towers are evaporative coolers used for cooling water or other

working medium to near the ambivalent web-bulb air temperature.

Cooling tower use evaporation of water to reject heat from processes

such as cooling the circulating water used in oil refineries, Chemical

plants, power plants and building cooling, for example. The tower 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 structure 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 primary use of large , industrial cooling tower system is to remove

the heat absorbed in the circulating cooling water systems used in

power plants , petroleum refineries, petrochemical and chemical plants,

natural gas processing plants and other industrial facilities . 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.

2.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

conductor material to transmit electric power than equivalent singlephase, 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. Taking one conductor as the reference, the

other two current are delayed in time by one-third and two-third of one

cycle of the electrical current. This delay between phases has the


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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.

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 one cycle. Generators output at a voltage that

ranges from hundreds of volts to 30,000 volts. 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

center 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 ( known as a wild leg) and neutral and 240 V between

any two phase) to be available from the same supply.

3.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 may

be a reciprocating or turbine steam engine, , water falling through theturbine are made in a variety of sizes ranging from small 1 hp (0.75 kW)

units (rare) used as mechanical drives for pumps, compressors and

other shaft driven equipment , to 2,000,000 hp(1,500,000 kW) turbines

used to generate electricity. There are several classifications for

modern steam turbines.


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Steam turbines are used in all of our 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 station use large stem turbines driving electric

generators to produce most (about 86%) of the worlds electricity.

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.

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 stage 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 into 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.

4.Boiler feed water 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 retuning

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


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6. Control valves

Control valves are valves used within industrial plants and elsewhere to

control operating conditions such as temperature,pressure,flow,and

liquid Level by fully 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

7. Deaerator

A Dearator 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 non-corrosive. 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 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. 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)

8. 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 waterreduces the irreversible involved in steam generation and therefore

improves the thermodynamic efficiency of the system.[4] This reduces

plant operating costs and also helps to avoid thermal shock to the

boiler metal when the feed water is introduces back into the steam

cycle.


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In a steam power (usually modeled as a modified Ranking cycle), feed

water heaters allow the feed water to be brought up to the saturation

temperature very gradually. This minimizes the inevitable

irreversibilitys associated with heat transfer to the working fluid

(water). 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.

9. Pulverizer

A pulverizer is a device for grinding coal for combustion in a furnace in

a fossil fuel power plant.

10. Boiler Steam 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 involves temperatures

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.

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 thesludge or sediments which have a tendency to the bottom.

11. Super Heater

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


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generated by the boiler again increasing its thermal energy and

decreasing the likelihood that it will condense inside the engine. 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 so

stationary steam engines including power stations.

12. 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, and 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 a

device fitted to a boiler which saves energy by using the exhaust gases

from the boiler to preheat the cold water used the 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 they are turbines before it is pumped to the

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

capture the waste hit 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.

13. 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


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useful heat lost in the fuel gas. As a consequence, the flue gases 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.

14. 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 application.

The original parallel plate-Weighted wire design (described above) has

evolved as more efficient ( and robust) discharge electrode designs

were developed, today focusing 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 and hopper evacuation systems remove the collected

particulate matter while on line allowing ESPs to stay in operation for

years at a time.

15. Fuel gas stack

A Fuel gas stack is a type of chimney, a vertical pipe, channel or similar

structure through which combustion product gases called fuel gases are

exhausted to the outside air. Fuel gases are produced when coal, oil,

natural gas, wood or any other large combustion device. Fuel gas is


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usually composed of carbon dioxide (CO2) and water vapor 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 sulfur 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 aria and thereby

reduce the concentration of the pollutants to the levels required by

governmental environmental policies and regulations.

When the fuel gases exhausted from stoves, ovens, fireplaces or other

small sources within residential abodes, restaurants , hotels or other

stacks are referred to as chimneys.


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ELECTRIC MOTORSAn electric motor uses electrical energy to produce mechanical energy. The reverse process

that of using mechanical energy to produce electrical energy is accomplished by a generator or

dynamo. Traction motors used on locomotives and some electric and hybrid automobiles often

performs both tasks if the vehicle is equipped with dynamic brakes.

Categorization of Electrical Motors

The classic division of electric motors has been that of Direct Current (DC) types vs Alternating

Current (AC) types. The ongoing trend toward electronic control further muddles the

distinction, as modern drivers have moved the commutator out of the motor shell. For this new

breed of motor, driver circuits are relied upon to generate sinusoidal AC drive currents, or

some approximation of. The two best examples are: the brushless DC motor and the stepping

motor, both being polyphase AC motors requiring external electronic control.

There is a clearer distinction between a synchronous motor and asynchronous types. In the

synchronous types, the rotor rotates in synchrony with the oscillating field or current (eg.

permanent magnet motors). In contrast, an asynchronous motor is designed to slip; the most

ubiquitous example being the common AC induction motor which must slip in order to

generate torque.


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Induction Motor

An electric motor converts electrical power to mechanical power in its rotor

(rotating part). There are several ways to supply power to the rotor. In a DC motor

this power is supplied to the armature directly from a DC source, while in an AC

motor this power is induced in the rotating device. An induction motor is sometimes

called a rotating transformer because the stator (stationary part) is essentially the

primary side of the transformer and the rotor (rotating part) is the secondary side.Induction motors are widely used, especially polyphase induction motors, which are

frequently used in industrial drives.

Induction motors are now the preferred choice for industrial motors due to their

rugged construction, lack of brushes (which are needed in most DC Motors) and

thanks to modern power electronics the ability to control the speed of the motor.

Construction


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The stator consists of wound 'poles' that carry the supply current that induces a

magnetic field in the conductor. The number of 'poles' can vary between motor

types but the poles are always in pairs (i.e. 2, 4, 6 etc). There are two types of rotor:

1. Squirrel-cage rotor

2. Slip ring rotor

The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid

copper (most common) or aluminum that span the length of the rotor, and are

connected through a ring at each end. The rotor bars in squirrel-cage induction

motors are not straight, but have some skew to reduce noise and harmonics.

The motor's phase type is one of two types:

1. Single-phase induction motor

2. 3-phase induction motor

Principle of Operation

The basic difference between an induction motor and a synchronous AC motor is

that in the latter a current is supplied onto the rotor. This then creates a magnetic

field which, through magnetic interaction, links to the rotating magnetic field in the

stator which in turn causes the rotor to turn. It is called synchronous because at

steady state the speed of the rotor is the same as the speed of the rotating magnetic

field in the stator.

By way of contrast, the induction motor does not have any direct supply onto the

rotor; instead, a secondary current is induced in the rotor. To achieve this, stator

windings are arranged around the rotor so that when energised with a polyphase

supply they create a rotating magnetic field pattern which sweeps past the rotor.

This changing magnetic field pattern can induce currents in the rotor conductors.

These currents interact with the rotating magnetic field created by the stator and

the rotor will turn.

However, for these currents to be induced, the speed of the physical rotor and the

speed of the rotating magnetic field in the stator must be different, or else the

magnetic field will not be moving relative to the rotor conductors and no currents

will be induced. If by some chance this happens, the rotor typically slows slightly

until a current is re-induced and then the rotor continues as before. This difference

between the speed of the rotor and speed of the rotating magnetic field in the stator

is called slip. It has no unit and the ratio between the relative speed of the magnetic

field as seen by the rotor to the speed of the rotating field. Due to this an induction

motor is sometimes referred to as an asynchronous machine.

Types:

Based on type of phase supply

1. three phase induction motor (self starting in nature)

2. single phase induction motor (not self starting)

Other

1. Squirrel cage induction motor

2. Slip ring induction motor


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SWITCHGEARThe term switchgear, used in association with the electric power system, or grid, refers to the

combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical

equipment. Switchgear is used both to de-energize equipment to allow work to be done and toclear faults downstream.

The very earliest central power stations used simple open knife switches, mounted on

insulating panels of marble or asbestos. Power levels and voltages rapidly escalated, making

open manually-operated switches too dangerous to use for anything other than isolation of a

de- energized circuit. Oil-filled equipment allowed arc energy to be contained and safely

controlled. By the early 20th century, a switchgear line-up would be a metal-enclosed structure

with electrically-operated switching elements, using oil circuit breakers. Today, oil-filled

equipment has largely been replaced by air-blast, vacuum, or SF6 equipment, allowing large

currents and power levels to be safely controlled by automatic equipment incorporating digital

controls, protection, metering and communications.

A view of switcgear at Power Plant


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Functions

One of the basic functions of switchgear is protection, which is interruption of short-

circuit and overload fault currents while maintaining service to unaffected circuits.

Switchgear also provides isolation of circuits from power supplies. Switchgear also

is used to enhance system availability by allowing more than one source to feed a

load.

Switchgear makes or breaks an electrical circuit.

1. Isolation: - A device which breaks an electrical circuit when circuit is switched on

to no load. Isolation is normally used in various ways for purpose of isolating a

certain portion when required for maintenance.

2. Switching Isolation: - It is capable of doing things like interrupting transformer

magnetized current, interrupting line charging current and even perform load

transfer switching. The main application of switching isolation is in connection withtransformer feeders as unit makes it possible to switch out one transformer while

other is still on load.

3. Circuit Breakers: - One which can make or break the circuit on load and even on

faults is referred to as circuit breakers. This equipment is the most important and is

heavy duty equipment mainly utilized for protection of various circuits and

operations on load. Normally circuit breakers installed are accompanied by

isolators

4. Load Break Switches: - These are those interrupting devices which can make or

break circuits. These are normally on same circuit, which are backed by circuitbreakers.

5. Earth Switches: - Devices which are used normally to earth a particular system,

to avoid any accident happening due to induction on account of live adjoining

circuits. These equipments do not handle any appreciable current at all. Apart from

this equipment there are a number of relays etc. which are used in switchgear.

LT Switchgear

It is classified in following ways:-

1. Main Switch:- Main switch is control equipment which controls or disconnects

the main supply. The main switch for 3 phase supply is available for tha range 32A,


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63A, 100A, 200Q, 300A at 500V grade.

2. Fuses: - With Avery high generating capacity of the modern power stations

extremely heavy carnets would flow in the fault and the fuse clearing the fault

would be required to withstand extremely heavy stress in process.

It is used for supplying power to auxiliaries with backup fuse protection. Rotary

switch up to 25A. With fuses, quick break, quick make and double break switch

fuses for 63A and 100A, switch fuses for 200A, 400A, 600A, 800A and 1000A are

used.

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

and protecting the connected motors.

4. Overload Relay: - For overload protection, thermal over relay are best suited for

this purpose. They operate due to the action of heat generated by passage of current

through relay element.

5. 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. This reduces the possibility of

sparking. The pressure may vary from 50-60 kg/cm^2 for high and mediumcapacity circuit breakers.

HT SWITCH GEAR

High voltage switchgear is any switchgear and switchgear assembly of rated voltage

higher than

1000 volts.

High voltage switchgear is any switchgear used to connect or to disconnect a part of

a high voltage power system.These switchgears are essential elements for the protection and for a safety

operating mode without interruption of a high voltage power system. This type of

equipment is really important because it is directly linked to the quality of the

electricity supply.

The high voltage is a voltage above 1000 V for alternating current and above 1500 V

for direct current.


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HT Switch Gear

1. 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.

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

Operating Coils-CC 220 V/DC

FC 220V/DC

Motor Voltage-220 V/DC

2. 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:-


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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

3. 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 o thatof air blast circuit breaker. It simply employs the arc extinguishing medium namely

SF6. the performance of gas . 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

Rated Short Time Current 1/3s -40 A

Mass Approximation-185 KG

Auxiliary Voltage

Closing Coil-220 V/DC

Opening Coil-220 V/DC

Motor-220 V/DC

SF6 Pressure at 20 Degree Celsius-0.25 KG

SF6 Gas Per pole-0.25 KG

4. Vacuum Circuit Breaker: - It works on the principle that vacuum is used to savethe purpose of insulation and it implies that pr. Of gas at which breakdown voltage

independent of pressure. It 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

Rated Current-1250 A

Supply Voltage Tripping-220 V/DC

Insulation Level-IMP 75 KVP Rated Short Time Current-40 KA (3 SEC)

Weight of Breaker-8 KG


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GENERATOR

The basic function of the generator is to convert mechanical power, delivered from

the shaft of the turbine, into electrical power. Therefore a generator is actually arotating mechanical energy converter. The mechanical energy from the turbine is

converted by means of a rotating magnetic field produced by direct current in the

copper winding of the rotor or field, which generates three-phase alternating

currents and voltages in the copper winding of the stator (armature). The stator

winding is connected to terminals, which are in turn connected to the power system

for delivery of the output power to the system.

A 210 MW Turbine Generator at Badarpur Thermal Power Station, New Delhi

The class of generator under consideration is steam turbine-driven

generators,commonly called turbo generators. These machines are generally used in

nuclear and fossil fueled power plants, co-generation plants,and combustion turbine


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units.They range from relatively small machines of a few Megawatts (MW) to very

large generators with ratings up to 1900 MW. The generators particular to this

category are of the two- and four-pole design employing round-rotors, with

rotational operating speeds of 3600 and 1800 rpm in North America, parts of Japan,

and Asia (3000 and 1500 rpm in Europe, Africa, Australia, Asia, and South

America). At Badarpur Thermal Power Station 3000 rpm, 50 Hz generators are

used of capacities 210 MW and 95 MW.

As the system load demands more active power from the generator, more steam (orfuel in a combustion turbine) needs to be admitted to the turbine to increase power

output. Hence more energy is transmitted to the generator from the turbine, in the

form of a torque. This torque is mechanical in nature, but electromagnetically

coupled to the power system through the generator. The higher the power output,

the higher the torque between turbine and generator. The power output of the

generator generally follows the load demand from the system. Therefore the

voltages and currents in the generator are continually changing based on the load

demand. The generator design must be able to cope with large and fast load

changes, which show up inside the machine as changes in mechanical forces and

temperatures. The design must therefore incorporate electrical current-carrying

materials (i.e., copper), magnetic flux-carrying materials (i.e., highly permeablesteels), insulating materials (i.e., organic), structural members (i.e., steel and

organic), and cooling media (i.e., gases and liquids), all working together under the

operating conditions of a turbo generator

An open Electric Generator at Power Plant

Working Principle

The A.C. Generator or alternator is based upon the principle of electromagnetic


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induction and consists generally of a stationary part called stator and a rotating

part called rotor. The stator housed the armature windings. The rotor houses the

field windings. D.C. voltage is applied to the field windings through slip rings. When

the rotor is rotated, the lines of magnetic flux (viz magnetic field) cut through the

stator windings. This induces an electromagnetic force (e.m.f.) in the stator

windings.

The magnitude of this e.m.f. is given by the following expression.

E = 4.44 /O FN volts0 = Strength of magnetic field in Webers.

F = Frequency in cycles per second or Hertz.

N = Number of turns in a coil of stator winding

F = Frequency = Pn/120

Where P = Number of poles

n = revolutions per second of rotor.

From the expression it is clear that for the same frequency, number of poles

increases with decrease in speed and vice versa. Therefore, low speed hydro turbine

drives generators have 14 to 20 poles where as high speed steam turbine driven

generators have generally 2 poles. Pole rotors are used in low speed generators,because the cost advantage as well as easier construction.

Generator component

This Chapter deals with the two main components of the Generator viz. Rotor, its

winding & balancing and stator, its frame, core & windings.

Rotor

The electrical rotor is the most difficult part of the generator to design. It revolves in

most modern generators at a speed of 3,000 revolutions per minute. The problem of

guaranteeing the dynamic strength and operating stability of such a rotor iscomplicated by the fact that a massive non-uniform shaft subjected to a multiplicity

of differential stresses must operate in oil lubricated sleeve bearings supported by a

structure mounted on foundations all of which possess complex dynamic be

behavior peculiar to themselves. It is also an electromagnet and to give it the

necessary magnetic strength the windings must carry a fairly high current. The

passage of the current through the windings generates heat but the temperature

must not be allowed to become so high, otherwise difficulties will be experienced

with insulation. To keep the temperature down, the cross section of the conductor

could not be increased but this would introduce

another problems. In order to make room for the large conductors, body and this

would cause mechanical weakness. The problem is really to get the maximumamount of copper into the windings without reducing the mechanical strength. With

good design and great care in construction this can be achieved. The rotor is a cast

steel ingot, and it is further forged and machined. Very often a hole is bored

through the centre of the rotor axially from one end of the other for inspection. Slots

are then machined for windings and ventilation.

Rotor winding


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Silver bearing copper is used for the winding with mica as the insulation between

conductors. A mechanically strong insulator such as micanite is used for lining the

slots. Later designs of windings for large rotor incorporate combination of hollow

conductors with slots or holes arranged to provide for circulation of the cooling gas

through the actual conductors. When rotating at high speed. Centrifugal force tries

to lift the windings out of the slots and they are contained by wedges. The end rings

are secured to a turned recess in the rotor body, by shrinking or screwing and

supported at the other end by fittings carried by the rotor body. The two ends of

windings are connected to slip rings, usually made of forged steel, and mounted on

insulated sleeves.

Rotor balancing

When completed the rotor must be tested for mechanical balance, which means that

a check is made to see if it will run up to normal speed without vibration. To do this

it would have to be uniform about its central axis and it is most unlikely that this

will be so to the degree necessary for perfect balance. Arrangements are therefore

made in all designs to fix adjustable balance weights around the circumference at

each end.

Stator

Stator frame: The stator is the heaviest load to be transported. The major part of

this load is the stator core. This comprises an inner frame and outer frame. Theouter frame is a rigid fabricated structure of welded steel plates, within this shell is a

fixed cage of girder built circular and axial ribs. The ribs divide the yoke in the

compartments through which hydrogen flows into radial ducts in the stator core

and circulate through the gas coolers housed in the frame. The inner cage is usually

fixed in to the yoke by an arrangement of springs to dampen the double frequency

vibrations inherent in 2 pole generators. The end shields of hydrogen cooled

generators must be strong enough to carry shaft seals. In large generators the frame

is constructed as two separate parts. The fabricated inner cage is inserted in the

outer frame after the stator core has been constructed and the winding completed.

Stator core: The stator core is built up from a large number of 'punching" or

sections of thin steel plates. The use of cold rolled grain-oriented steel can contributeto reduction in the weight of stator core for two main reasons:

a) There is an increase in core stacking factor with improvement in lamination cold

Rolling and in cold buildings techniques.

b) The advantage can be taken of the high magnetic permeance of grain-oriented

steels of work the stator core at comparatively high magnetic saturation without

fear or excessive iron loss of two heavy a demand for excitation ampere turns

from the generator rotor.

Stator WindingsEach stator conductor must be capable of carrying the rated current without

overheating. The insulation must be sufficient to prevent leakage currents flowing

between the phases to earth. Windings for the stator are made up from copper

strips wound with insulated tape which is impregnated with varnish, dried under

vacuum and hot pressed to form a solid insulation bar. These bars are then place in

the stator slots and held in with wedges to form the complete winding which is

connected together at each end of the core forming the end turns. These end turns


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are rigidly braced and packed with blocks of insulation material to withstand the

heavy forces which might result from a short circuit or other fault conditions. The

generator terminals are usually arranged below the stator. On recent generators

(210 MW) the windings are made up from copper tubes instead of strips through

which water is circulated for cooling purposes. The water is fed to the windings

through plastic tubes.

TRANFORMER& SWITCHYARD

A transformer is a device that transfers electrical energy from one circuit to another

by magnetic coupling with out requiring relative motion between its parts. It usually

comprises two or more coupled windings, and in most cases, a core to concentrate

magnetic flux. An alternating voltage applied to one winding creates a time-varying

magnetic flux in the core, which includes a voltage in the other windings. Varying

the relative number of turns between primary and secondary windings determines

the ratio of the input and output voltages, thus transforming the voltage by stepping

it up or down between circuits. By transforming electrical power to a high-voltage,_low-current form and back again, the transformer greatly reduces energy

losses and so enables the economic transmission of power over long distances. It has

thus shape the electricity supply industry, permitting generation to be located

remotely from point of demand. All but a fraction of the worlds electrical power

has passed trough a series of transformer by the time it reaches the consumer.

Basic principles

The principles of the transformer are illustrated by consideration of a hypothetical

ideal transformer consisting of two windings of zero resistance around a core of

negligible reluctance. A voltage applied to the primary winding causes a current,

which develops a magneto motive force (MMF) in the core. The current required to

create the MMF is termed the magnetizing current; in the ideal transformer it is

considered to be negligible, although its presence is still required to drive flux

around the magnetic circuit of the core. An electromotive force (MMF) is induced

across each winding, an effect known as mutual inductance. In accordance with

faradays law of induction, the EMFs are proportional to the rate of change of flux.

The primary EMF, acting as it does in opposition to the primary voltage, is

sometimes termed the back EMF. Energy losses An ideal transformer would have

no energy losses and would have no energy losses, and would therefore be 100%

efficient. Despite the transformer being amongst the most efficient of electrical

machines with ex the most efficient of electrical machines with experimental models

using superconducting windings achieving efficiency of 99.85%, energy is dissipated

in the windings, core, and surrounding structures. Larger transformers are

generally more efficient, and those rated for electricity distribution usually perform

better than 95%. A small transformer such as plug-in power brick used for low-

power consumer electronics may be less than 85% efficient. Transformer losses are

attributable to several causes and may be differentiated between those originated in

the windings, some times termed copper loss, and those arising from the magnetic

circuit, sometimes termed iron loss. The losses vary with load current, and may


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furthermore be expressed as no load or full load loss, or at an intermediate

loading. Winding resistance dominates load losses contribute to over 99% of the no-

load loss can be significant, meaning that even an idle transformer constitutes a

drain on an electrical supply, and lending impetus to development of low-loss

transformers. Losses in the transformer arise from: Winding resistance Current

flowing trough the windings causes resistive heating of the conductors. At higher

frequencies, skin effect and proximity effect create additional winding resistance

and losses. Hysteresis losses Each time the magnetic field is reversed, a small

amount of energy is lost due to hysteresis within the core. For a given core material,

the loss is proportional to the frequency, and is a function of the peak flux density to

which it is subjected. Eddy current Ferromagnetic materials are also goodconductors, and a solid core made from such a material also constitutes a single

short-circuited turn trough out its entire length. Eddy currents therefore circulate

with in a core in a plane normal to the flux, and are responsible for resistive heating

of the core material. The eddy current loss is a complex function of the square of

supply frequency and inverse square of the material thickness. Magnetostriction

Magnetic flux in a ferromagnetic material, such as the core, causes it to physically

expand and contract slightly with each cycle of the magnetic field, an effect known

as magnetostriction. This produces the buzzing sound commonly associated with

transformers, and in turn causes losses due to frictional heating in susceptible cores.

Mechanical losses In addition to magnetostriction, the alternating magnetic field

causes fluctuating electromagnetic field between primary and secondary windings.These incite vibration with in near by metal work, adding to the buzzing noise, and

consuming a small amount of power. Stray losses Leakage inductance is by itself

loss less, since energy supplied to its magnetic fields is returned to the supply with

the next half-cycle. However, any leakage flux that intercepts nearby conductive

material such as the transformers support structure will give rise to eddy currents

and be converted to heat. Cooling system Large power transformers may be

equipped with cooling fans, oil pumps or water-cooler heat exchangers design to

remove heat. Power used to operate the cooling system is typically considered part

of the losses of the transformer.


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A 220 kV Transformer at Power Plant

PROTECTION

The protection system of any modern electric power grid is the most crucial

function in the system. Protection is a system because it comprises discrete devices(relays, communication means, etc.) and an algorithm that establishes a coordinated

method of operation among the protective devices. This is termed coordination.

Thus, for a protective system to operate correctly, both the settings of the individual

relays and the coordination among them must be right. Wrong settings might result

in no protection to the protected equipment and systems, and improper

coordination might result in unwarranted loss of production. The key function of

any protective system is to minimize the possibility of physical damage to equipment

due to a fault anywhere in the system or from abnormal operation of the equipment(over speed, under voltage, etc.). However, the most critical function of any

protective scheme is to safeguard those persons who operate the equipment that

produces, transmits, and utilizes electricity.

Protective systems are inherently different from other systems in a power plant (or

for that matter any other place where electric power is present). They are called to


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Typically it will alarm, but it can also be set to trip the unit. Protections function

can also be divided into short- circuit protection functions. The short-circuit

protection comprises impedance, distance, and current differential protection.

Multi-function Generator Protection Device

GENERATOR PROTECTIVE FUNCTION

Protection devices are designed to monitor certain conditions, and subsequently, to

alarm or trip if a specified condition is detected. The condition is represented by a

function or protective function code. Thus there is a relay for every protective

function. If a relay only monitors and thus protects against a single set of conditions,

it is said that the relay is a single-function device. In the past most relays were

single-function devices. With the advent of solid-state electronics, manufacturers

have combined several functions in one unit or device.

These multi-function relays or protective devices offer specific protective

functions designed for certain types of apparatus. Some multi-function relays are

dedicated to transformers, others to motors, and others to generators. Advances in

solid-state electronics have led to less costly devices. Today a multi-function solid-

state device with, for instance, five protective functions, is less expensive than five

separate relays for five protective functions.


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The number of functions covered by different relays and the number of

multifunction devices are decided, among other things, by the expected losses of all

the protective functions covered by the multi-functional relay, if that particular

device becomes faulty. A multi-functional relay containing all the protective

functions required for the protection of a generator can be combined with a few

discrete relays providing backup protection for critical functions. Alternatively, two

or more multi-functional relays can be applied, providing partial or comprehensive

redundancy. There are many combinations of these discrete and multi-functional

relays that can be adopted, depending on when the power plant was build, the size

of the units, system conditions, the idiosyncrasy of the designer, and many other

factors. Alternatively, two or more multi-functional relays can be applied, providing

partial or comprehensive redundancy. There are many combinations of these

discrete and multi-functional relays that can be adopted, depending on when the

power plant was build, the size of the units, system conditions, the idiosyncrasy of

the designer, and many other factors.

Relays or protection devices are divided into two categories according to how they

process data. The first category is that of analog relays; the second is that of

numerical (also called digital) relays. Bear in mind that a relay can be electronic but

still process the data in an analog manner. The advantages of numerical processing

are various. Accuracy is enhanced. So is flexibility in use. For instance, a numerical

relay offers user-shaped protection widows such that the user can change the shape

of the operation/non-operation areas for a specific function of the relay.

Furthermore the shape of the region of operation may change according to system

conditions (adaptive function).

Finally, there is rather a newstill evolvingapproach (from the early 1990s) for

protecting large generating units by the so-called expert protection systems. The

idea is to protect the unit based not only on the basic protective functions (given

below), but also as a combination of protective and monitoring data and built-in

expertise in the form of diagnostic prescriptions. Invariably, building the expertise

base of these systems consists in expressing probable causes for a particular

combination of symptoms, expressed as a probabilistic tree.

A number, according to a worldwide-accepted nomenclature, identifies protectivefunctions. The functions shown in table are typical of generation protection. A

number of the functions included in table are so important that they will always find

their way into the protection scheme of any generator (e.g., 25, 59, and 87). Others

may be omitted in some applications (e.g., 49). The larger and more expensive the


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Trainee Report Ntpc[1]

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Transcript of Trainee Report Ntpc[1]