Co-generation Power Plant.

8/9/2019 Co-generation Power Plant.

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CONTENTS

CHAPTER.1

COGENERATION

1. Cogeneration - 1

2. Introduction - 1

3. Choice of site - 2

CHAPTER.2

MAIN REQUIREMENTS - 3

1. Fuel - 4

2. Feed water - 4

3. Water treatment plant - 4

4. Boiler - 4

5. Boiler furnace - 6

6. Super heater - 7

7. Economiser - 8

8. Air preheater & types - 9

9. Condenser - 11

10. Turbines - 16

11. Alternators - 17

11.1. Introduction - 17

11.2. Operating principle - 17

11.3. Classification - 17

11.4. Types of alternators - 18

11.5. Construction - 19


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11.6. Types of rotor - 19

11.7. Classification based on the prime mover - 20

12. Transformers

12.1. Single phase transformers - 21

12.2. Construction - 21

12.3. Three phase transformers - 22

12.4. Three phase connections - 25

12.4.1. - Connection -25

12.4.2. Y- connection - 26

12.5. Instrument transformers - 26

12.5.1. Current transformers

12.5.2. Potential transformers

12.6. Losses in transformers - 27

12.7. Cooling methods - 28

13. VFD - 29

14. ESP - 30

CHAPTER.3

SCHEMATIC ARRANGEMENT OF PLANT - 30-34

CONCLUSION

BIBLIOGRAPHY


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CHOICE OF SITE FOR CO-GENERATION PLANT:

1. Supply of fuel: Bagasse is available from sugar factory. So such a plant isto be installed in or near sugar factory.

2. Availability of water: A huge amount of water is required for thecondenser; therefore, such a plant should be located atthe bank of a river

or near the canal or bore wells to ensure continuous supply of water.

3. Transport facilities: A co-generation plant often requires thetransportation of sugarcane and machinery.

4. Nearness to load centers: In order to reduce the transmission cost theplant should be located near the centre of the load. In thecase of A.Csupply system the transformation of energy from lower voltage to higher

voltage and vice versa is possible.

5. Distance from populated area: Due to air pollution it has to beconstructed far away from the population.

6. Land requirement: The land is required not only for setting of the plant but for other purposes such as staff colony, disposal of ash or fuel

storage. Land should be also available for future extensions

7. Ash disposal: Ash is the main waste product of the steam power plant.The ash may be purchased by building contractors, or it can be used for

brick making near plant site. The site is nearer to river or sea or lay ash

can be dumped into it. If the waste land is available near the site then thearea of 40 hectares excavated to a depth of 6.5 meters will be required

per year for a 2000 MW plant.

8. Labour supplies : Skilled and unskilled labours must be available atreasonable rates near the site of the plant

9. Type of the land: Land should be available such that it has good bearingcapacity to with stand not only the dead load of the plant but also the

forces transmitted to the foundation due to the operation of the plant and

this total land may amount to about 7kg/cm more over the land should bereasonably level and not low lying.


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2.


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MAIN REQUIREMENTS

FUEL

FEED WATER PLANT

BOILER

SUPER HEATER

ECONOMIZER

AIRPREHEATER

CONDENSER

COOLING TOWER

INDUCED DRAUGHT FAN

FORCED DRAUGHT FAN

CHIMNEY

TURBINES

REDUCTION GEAR BOX

ALTERNATOR

TRANSFORMERS


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3.

FUEL

The main source of energy is fuels. The fuels may be solid, liquid, or gases such as coal,oil and coal gas.

Here we use Bagasse as fuel for generation of electrical energy

Sugarcane waste is known as Bagasse. It is available from sugar industry, where

sugarcane is crushed to get sugarcane juice and Bagasse is used to generate electric power. The

calorific value of Bagasse is 2500 kcal/kg. It is also used in paper industry. To generate a ton of

steam, two tones of Bagasse; has to be burnt.30 to 33% of Bagasse is present in sugarcane.

Bagasse is a good firing material.

FEED WATER

The condensate from the condenser is used as feed water to the boiler. Some water maybe lost in the cycle which is suitably made up from external source. The feed water on its way tothe boiler is heated by water heaters and economizer. This helps in raising the overall efficiency

of the plant.

WATER TREATMENT PLANT

Boilers require clean and soft water for long life and better efficiency. However the

source of boiler feed water is generally a river or a lake or bore wells which may containsuspended and dissolved impurities, dissolved gases etc. Therefore, it is very important that

water is first purified and softened by chemical treatment and then delivered to the boiler.

The suspended impurities are removed through sedimentation, coagulation and filtration.

Dissolved gases are removed by aeration and degasification. The water is then softened by

removing temporary and permanent hardness through different chemical processes. The pure andsoft water thus available is fed to the boiler for steam generation.

Here we use reverse osmosis plant for removing the impurities in the raw water. This

method consists of thin permeable membrane for removing impurities.

BOILER:

Boilers or steam generators convert water into steam and form one of the majorequipments of the plant.

A boiler is a closed vessel in which water is converted into steam by utilizing the heat

combustion of Bagasse. Boilers are twoTypes. They are;

1. Water tube boiler

2. Fire tube boiler


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4.

In fire tube boilers the tubes containing the hot products of combustion pass through the

tubes surrounded by water. Water tube boiler has number of advantages over fire tube boiler,

requires less space, smaller size of tubes and drum, high working pressure due to small drum,

less liable to explosion etc. Therefore, the use of water tube boiler has become universal. Fromthe above advantages we are using water tube boilers in Co-generation plant. Boiler capacity is

64 tones in 6MW co-generation plant

In the water tubes boilers the water is inside the tubes and the hot gases are outside the

tubes as the water and steam are in the same shell, higher pressure of steam are not possible. The

output steam has a pressure of 42Kg/cm2 and temperature of 4150c the temperature of boiler is

14000c.

Here we use Water tube boilers.

Water tube boilers consist of drums and tubes. The tubes are always external to drum. In

comparison to fire tube boilers the drum in such boiler dont contain any tubular heating surfaces

so they can be build in smaller diameters and consequently they will withstand the high pressure.

The advantages of water tube boilers over the fire tube boilers are as under;

High evaporation capacity due to availability of large heating surfaces

Better heat transfer to the mass of water and better efficiency of plant and owing

to rapid and uniform circulation of water in tubes

High working pressure due to smaller size of drum

Quick raising of steam owing to large ratio of heating surface to water volume

Safety in operation Less space occupied

Better overall control

Easy removal of scale from inside of the tubes

It is one of the best types of vertical multi-tubular boiler, and has a number of horizontalfire tubes. Cochran boiler consists of a cylindrical shell with a dome shaped top where the space

is provided for steam. The furnace is one piece construction and seamless. Its crown has a

hemispherical shape and thus provides maximum volume of space.

BABCOCK AND WILCOX WATER TUBE BOILER:

The water tube boilers are used exclusively, when pressure above 10 bars and capacity inexcess of 7000 Kg of steam per hour is required. Babcock and Wilcox water tube boiler is an

example of horizontal straight tube boiler.

A Babcock and Wilcox water tube boiler with cross drum differs from

longitudinal drum boiler in a way that how drum is placed with reference to the axis of the watertubes of the boiler. The longitudinal drum restricts number of tubes that can be connected to one

drum circumferentially and limits the capacity of the boiler. In the cross drum there is no

limitation of the number of connecting tubes.


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5.

The fuel is burnt on the grate and ash is collected and disposed of from ash pit. The gasesof combustion produced by burning of fuel enter the combustion chamber through the flue tube

and strike against fire brick lining which directs them to pass through number of horizontal

tubes, being surrounded by water. After which the gases escape to the atmosphere through smokebox and chimney. A number of hand holes are provided around the outer shell for cleaning

purposes.

The selection and size of the boiler depends upon

1. Output requires in terms of amount of steam/hour, operating temperature and pressure

2. Availability of fuel and water3. The probable load factor

The other factors which influence the choice of a boiler are availability, initial cost,

maintenance cost, labor cost, fuel cost and space requirements.

The water tube boilers are used where large amount of steam are to be produced at a hightemperature and pressure and weight and space considerations are important. To meet a required

demand, the choice between two boilers will be based on economic considerations I.e., total

annual; cost (fixed cost running cost). The worth nothing point is that the total cost of the fuel

used by the boiler in its life time may be 3 to 4 times the initial investment.

BOILER FURNACE

It is a chamber in which fuel is burnt to liberate the heat energy. The boiler furnace walls

are made of refractory materials such as fire clay, silica, kaolin etc; Bagasse is thrown into boiler

furnace through elevator.

The construction of boiler furnaces varies from plain refractory walls to completely to

water cooled walls, depending upon the characteristics of fuel used and ash produced, firingmethods , natural of load demand, combustion space required, excess air used, operating

temperature, initial and operating cost.

The plain refractory walls are suitable for small plants where the furnaces temperaturemay not be high. The arrangement may consists of a single section of homogenous refractory or

insulation may be placed in between the refractory and casing.

For large plants, where the furnace temperature is quite high refractory walls are made

hallow and air is circulated through hallow space to keep the temperature of the furnace walls

low. This type of arrangement is no more preferred.

Practically water cooled walls similar to plain refractory type with a portion of surface

covered by water tubes. A proper balance can be made between the water cooled section and the


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refractory section to give best results. This type is used for both stoker fired and pulverized fuel

fired boilers.

6.The recent development is to use water walls. The water walls are built of tubes of

diameter ranging from 25mm to 100mm variously spaced with or without fins or studs and bear

or with different thickness of moldable refractory on the inner face. Heat transfer rates run from0.5*106 to 1.4*106kcal/hour/m3of surface to meet these requirements of heat transmission,

circulation on the water side must be adequate, obtained by convection or by pumps. This type is

suitable for pulverized fuel fired boilers and high steaming rates can be maintained.

SUPERHEATER

A superheater is a device which superheats the steam. It raises the temperature of steamabove boiling point of water. A superheater consists of a group of tubes made of special alloy

steel such as chromium-molybdenum. These tubes are heated by the heat of flue gases during

their journey from the furnace to the chimney. The steam produced in the boiler is led through

the superheater where it is superheated by the heat of flue gases.

Super heaters consists of groups of tubes made of steel (carbon steel for steamtemperature up to 9500f, carbon-molybdenum steel for steam temperature of 10500f and stain less

steel for steam temperature of 12000f) with an outside diameter ranging from 25mm to 64mm.

tube handle location and arrangement, with counter current, and /or parallel flow is dictated by

type of firing, and required steam temperature, and steam temperature characteristic. Thesuperheater tubes are heated by heat of combustion gases during their passage from furnace to

chimney.

Super heaters are mainly classified into two types according to the system of heat transfer

from flue gases to steam. They are;

1. Radiant superheater

2. Convection superheater

Here in this power generation we are using radiant type superheater.

The radiant superheater is placed in the furnace between the water walls and receives heat

from the burning fuel through radiation process. It has two main disadvantages firstly, owing tohigh furnace temperature; it may get over heated and, therefore, requires a careful design.

Secondly it gives drooping characteristics i.e., the temperature falls with the increase in steam

output, the furnace temperature raises at a much less rapid rate then the steam output and theradiant heat transfer being a function of furnace temperature increases slowly with the steam

flow or the steam temperature falls.

On the other hand, a convection superheater is placed in the boiler tube bank and receives

heat from flue gases entirely through the convention process. It gives raising characteristics i.e.,

the temperature of the superheat increases with the increase in steam output because with the


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8.

The use of an economiser entails the following advantages

o The temperature range between various parts of the boiler is reduced which

results in reduction of stress due to unequal expansion.

o If the boiler is fed with cold water it may result in chilling the boiler metal. Hot

feed water checks it.

o Evaporative capacity of the boiler is increased.

o Overall efficiency of the plant is increased.

o Reduces temperature stresses in boiler joints.

In the modern economiser the temperature of feed water is raised from about 247 0c to

2760c

AIR PRE-HEATER

Super heaters and economizers generally cannot fully extract the heat from flue gases.

Therefore, pre-heaters are employed which recover some of the heat in the escaping gases.

The function of an air pre-heater is to extract heat from the flue gases and give it to the

air being supplied to furnace for fuel combustion. This raises the furnace temperature and

increases the thermal efficiency of the plant. Depending upon the method of transfer of heat from

flue gases to air, air pre-heaters are divided into the following two classes

1. Recuperative type

2. Regenerative type

The recuperative type air pre-heater consists of a group of steel tubes. The flue gases are

passed through the tubes while the air flows externally to the tubes. Thus heat of flue gases istransferred to air.

There are two types of Air preheaters

1. Tubular type

2. Plate type

1. Tubular type

After leaving the boiler or economizer the gaseous products of combustion travel

through the inside of the tubes of air preheater in a direction opposite to that of air travel and

transfer some of their heat to the air to be supplied to the furnace. Thus the air gets initially


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heated before being supplied to the furnace. The gases reverse their direction near the bottom of

the air heater, and a soot hopper is fitted to the bottom of air heater casing to collect soot

9.

2. Plate type

In the plate type Air preheater the air absorbs heat from the hot gases being sweptthrough the heater at high velocity on opposite side of a plate.

REGENERATIVE TYPE

The regenerative type air pre-heater consists of slowly moving drum made of corrugated

metal plates. The flue gases flow continuously on one side of the drum and air on the other side.

This action permits the transference of heat of flue gases to the air being supplied to the furnace

for fuel combustion.


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10.

CONDENSER

Steam after expansion through the prime mover goes through the condenser which

condenses the exhaust steam and also removes air and other non condensable gases from steam

while passing through them. The recovery exhaust steam in the condenser reduces the make up

feed water that must be added to the system from 100% when exhausted to atmosphere to about

1-5% and there by reduce condensable the capacity of water treatment plant. The exhaust

pressure may be lowered from the standard atmospheric pressure to about 25mm of Hg absolute

and there by permitting expansion of steam in the prime mover to very low pressure and

increasing plant efficiency. Maintenance of high vacuum in the condenser is essential for

efficient operation. Any leakage of air in to the condenser destroys the vacuum and causes

i. Any increase in the condenser pressure which limits the useful heat drop in the

prime mover

ii. A lower of the partial pressure of the steam and of the saturation temperature

along with it. This means that the latent heat increase and therefore, more cooling

water are required. Also, the under cooling of the condensate is likely to be more

severe.

This will result in lower efficiency. As it is not possible to eliminate air leakage

completely, a vacuum pump is necessary to remove the air leakage in to the condenser.

Condensers are of two types. Namely

Jet or contact condenser

Surface condenser

The essential differences between a jet condenser and surface condenser is that in the

former, the exhaust steam mixes with the cooling water and the temperature of the condensate

and the cooling water is the same when leaving the condenser; and the condensate cannot be

recovered for use as feed water to the boiler; heat transfer is by direct conduction; in the later i.e.

in surface condenser the exhaust steam and cooling water do not mix with each other, the water

being circulated through the nest of tubes, the heat transfer being by convection. The temperature


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of the condensate may be higher than the temperature of the cooling water at outlet and the

condensate is recovered as feed water to the boiler.

11.

Both the cooling water and the condensate are separately with drawn. Advantages of jetcondensers are;

Low initial cost

Low requirements of floor area and cooling water and

Low maintenance charge

Disadvantages

Condensate is wasted

High power is required for pumping water

Hence the use of jet condenser is limited to small industrial applications (1000kW) where

high vacuum is not required (50mm-125mm Hg abs).

The jet condensers may be further classified as

1. Parallel flow type jet condensers

2. Counter- flow type jet condensers


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12.


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13.


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14.


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15.


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Steam turbines are generally classified

into two types according to the action of

steam on moving blades viz.

Impulse turbines

Reaction turbines

THE IMPULSE TURBINE

In the case of the impulse turbine,

high velocity gases operate on the concave

surfaces of the blades almost exclusively. Inother words, this is a "bucket effect" means

of extracting energy.

Gas directed into the concave surfaceof the blades and at an angle of about 45 to85 degrees, relative to the shaft, will transfer

power to the shaft through impulse.

The unique characteristic of impulseengines is that the velocity of the gas

decreases upon exiting the blades, whereas

the pressure remains constant. Energy is

transferred by changing the velocity of thegas -- not its pressure.

The reaction blade acts like a wing

section of a plane, whereas the impulse

blade acts like the piston of an engine.

THE REACTION TURBINE

In the reaction turbine, kinetic gas

energy is converted to shaft power by

decreasing the velocity of the gas andlowering gas pressure -- just like on an

airplane wing. As gas enters from the left ofthe blade section and travels across the bladesurface, there is a decrease in pressure on

the upper surface, and an increase in

pressure on the lower surface. As the gas

leaves the trailing edge there is a decrease in

gas velocity, pressure, and a downwardangle -- resulting in a lifting or reaction

force.

Fig impulse turbine

Fig reaction turbine

16.


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ALTERNATORS

Introduction

A synchronous machine is an ac machine in which the rotor moves at a speed which

bears a constant relationship to the frequency of currents, in the armature winding. A

synchronous machine is one of the important types of electrical machines. Large ac networks

operating at constant frequency of 50Hz (or60Hz) rely almost exclusively on synchronous

generators, also called the alternators.

Synchronous motors provide constant speed industrial drives with the possibility of

power factor correction.

Synchronous machines are generally constructed in larger sizes. Small sizes alternators

are not economical. The modern trend is to build alternators of very large sizes capable of

generating 500MVA or even more. The synchronous motor is rarely built in small sizes owing to

superior performance characteristics and economical construction of induction motors.

Operating principle

The operating principle of a synchronous machine is fundamentally is same that of a dc

machine, but ,unlike the latter, in the synchronous machine there is no need to rectify the time

varying emf which is induced in the armature winding consequently a synchronous machine does

not require a commutator it is , in fact quite possible to use a dc generator as an alternator by

placing a set of collector rings on the shaft and connecting these rings to the proper points on the

armature winding; brushes riding on the rings can be collected to the load but unlike dc generatorthey are to be driven at a very definite constant speed as the frequency of a generated emf is

determined by that speed the latter is usually referred to as synchronous speed , for which reason

these machines are called frequently synchronous generators.

Synchronous generators, because of the absence of commutator are comparatively

simple and possesses several important advantages over the dc generators

Classification of Synchronous Machines

Synchronous machines, according to their applications, may be synchronous generators,

synchronous motors or synchronous compensators. A synchronous generator is a synchronous

machine which receives mechanical energy from a prime mover to which it is mechanically

coupled and delivers electrical energy. A synchronous motor receives electrical energy from ac

supply main and drives mechanical load.

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(a) Based on the construction of the machines, the synchronous machines can be classified as

1. Rotating Armature type,

2. Rotating Field type.

Rotating Armature type Alternator

It looks very much like a dc generator except that there are three slip rings in place of

commutator in such generators the required magnetic field is produced by dc electro magnets

placed on the stationary member called thestatorand the current generated is collected by the

means of brushes and slip rings on the revolving member called the rotorsuch an arrangement is

a economical for a small low voltage generator. Rotating armature type alternators are built only

in small ratings up to 200 or 250 KVA, because the voltage generated is comparatively low and

the current to be collected by the brushes are small. It practically all medium and large machines

are always constructed with revolving field.

1. This type of alternator has stationary field poles and rotating armature

2. It is mainly for small KVA capacity and low voltage rating

3. It resembles dc generator except that it has slip rings instead of commutator

4. Field poles are excited by an external dc source.

Rotating field type alternator

1. It has stationary armature (stator) and a rotating field poles

2. In this structure the rotor has slip rings and brushes to supply an excitation current from an

outside dc source.

3. The armature coils are placed in slots in a laminated core called the stator which is made up of

thin steel laminations and are placed in the frame of generators.

4. The amount of power delivered to the field circuit is relatively small that is 100-250 volts.

5. Most of the alternators are of this type and they are used for high KVA capacity and high

voltage rating.

Advantages of Rotating field type alternator:

1. The armature winding must be insulated for a high voltage while the voltage of field circuit is

low, because it is much easier insulate the high voltage winding. When it is mounted on

18.


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Stationary structure

2. Only a small amount of power at low voltage is handled by the slip ring contacts.

3. It is easier to build and balance high speed rotor when they carry field structure.

4. The armature winding is cooled more readily because the stator can made up of many air

passages or ducts for forced air circulation.

Construction of an Alternator:

In alternator consists of two parts

1. Stator

2. Rotor

The stator of the alternator consist of the alternator consist of a cast iron or welded steel

frame which supports the armature core having slots on its periphery for similar

conductors are connected together in groups to form a winding of desired no. of faces.(generally

star connected).

Ventilating ducts are provided parallel to the axis of frame to facilitate improved cooling

conditions.

The stator is made up of steel alloy laminations and the laminations are insulated fromeach other by a layer of oxide and enamel.

It is made up of laminations to reduce iron losses due to eddy currents.

Open windings are permitted because it is easy for the installation of stator coils and forthe removal in case of repair.

A fractional rather than integral no. of slots for pole is used to eliminate the harmonics inthe waveform.

Rotor

The rotors are classified into two types.

1. Salient pole type rotor

2. Smooth cylindrical type rotor

Salient Pole Type Rotor

This type of rotor is used carries large no. of poles (p>4).this type of rotor is used for

slow speed machines which have larger diameter and small axial length.


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Special features of salient pole type rotors:

19.

1Tthey have larger diameter and small axial length.

2. The pole shoe covers 2/3of the pole pitch.

3. The poles are laminated to reduce eddy currents losses. These types of rotors are employed

with water or hydro turbines and internal combustion engines.

4. Low operating speed.

5. This rotor have always vertical configuration.

Smooth cylindrical Type rotor (non salient pole)

The no. of poles of the rotor is less i.e. either two or four. This type of rotor is used for

alternators which are couple to steam turbines which run at very high speed.

Special features of cylindrical type rotors

1. They have smaller diameter and long axial length.

2. Robust construction.

3. Dynamic balancing is better.

4. High operating speeds.

5. Less windage losses.

7. Better emf waveform.

(b)Classification of synchronous machines based on prime mover

Synchronous machines are classified into two types based on the type of prime mover

1. Turbo generators

2. Hydro generators.

Turbo generators

If the generators are driven by steam turbines they are called as turbo generators. They

run at high speeds and the rotor will be of cylindrical type.


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2. Hydro generators

If the generators are driven by water turbines then they are called as hydro generators.

They run at low operation speeds. The rotor is if salient pole type.

20.

SINGLE PHASE TRANSFORMER

The transformer is probably one of the most useful electrical devices ever invented .It can

raise or lower the voltage or current in an AC Circuit, it can isolate circuits from each other, & it

can increase or decrease the apparent value of capacitor, an in doctor or a resistor. Further more,

the transformer enables us to transmit electrical energy over great distances & to distribute it

safely in factories & homes.

A transformer is static piece of apparatus by means of which electrical power in one

circuit is transformed into electrical power of the same frequency in another circuit. The physical

basis of transformer is mutual induction between two circuits linked by a common magnetic flux.

In its simplest form, it consists of two inductive coils which are electrically separated but

magnetically coupled through a path of low reluctance. The two coils possess high mutual

inductance. If one of the coil is connected to a source of alternating voltage, an alternating flux is

set up in the laminated core, most of which is linked with the other coil in which it produces

mutually induced emf according to Faradays laws of electromagnetic induction. If the second

coil is closed, a current flow in it & so electrical energy is transferred from first coil to second

coil. The first coil, in which electrical energy is fed from the AC supply, is called primary

winding and the other from which energy is drawn out, is called secondary winding.

Construction of the transformer

The simplest elements of the transformer consist of two coils having mutual inductance

and a laminated steel core. The two coils are insulated from each other and the steel core. Other

necessary parts are:

A suitable medium for insulating the core & its windings from itscontainer

A suitable bushings for insulating & bringing out the terminals of

the windings from the tank

In all types of transformers, the core is constructed of transformer sheet steel laminations

assembled to provide continuous magnetic paths with minimum of air gap included. The steel

used is of high silicon content, some times heat treated to produce a high permeability and a low

hysteresis loss at usual operating flux densities. The eddy current loss is minimized by


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laminating the core, the laminations being insulated from each other by a light coat of core plate

varnish or by an oxide layer on the surface.

21.

Transformer rating

Cu loss of a transformer depends on current and iron loss on voltage. Hence, total

transformer loss depends on volt-ampere (VA) and not on phase angle between voltage and

current i.e. it is independent of load power factor. Thats why rating of transformer is in KVA

and not in KW.

THREE PHASE TRANSFORMER

Large scale generation of electric power is usually 3-phase at generated voltages of

110,132,275,400 and 750 kV for which purpose 3-phase transformers are necessary to step up

the generated voltage to that of the transmission line. Next, at load centers, the transmission

voltages are reduced to distribution voltages of 6600, 4600 and 2300 volts. Further, at most of

the consumers, the distribution voltages are still reduced to utilization voltages of 440, 220 or

110 volts.

Years ago, it was a common practice to use suitably interconnected three single-phase

transformers instead of a single three phase transformer. But these days, the latter is gaining

popularity because of improvement in design and manufacture but principally because of better

acquaintance of operating men with the three phase type. As compared to a bank of single phase

transformer, the main advantages of a 3-phase transformer are that it occupies less floor space for

equal rating, weighs less, costs about 15% less and further, that only one unit is to be handled

and connected.

Like single phase transformers, the 3-phase transformers are also of the core type or shell

type. The basic principle of a 3-phase transformer is illustrated in figure 1in which only primary

windings have been shown inter connected in star and put across three phase supply. The three

cores are 1200 apart and their empty legs are shown in contact with each other. The center leg

formed by these three carries the flux produced by 3-phase currents IR, IY and IB. as at any instant

IR+ IY +IB=0

Hence the sum of three fluxes is also zero. Therefore, it will make no difference if the

common leg is removed. In that case any two legs will act as the return for the third just as in a

three phase system any two conductors act as the return current in the third conductor. This

improved design is shown in fig2.Where dotted rectangles indicate the 3 windings and numbers

in the cores and yokes represent the directions and magnitudes of fluxes at a particular instant. It


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will be seen that at any instant, the amount of up flux in any leg is equal to the sum of down

fluxes in the other two legs. The core type transformers are usually wound with circular

cylindrical coils.

22.


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Fig.1

23.


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Fig2

In a similar way, three 1-phase shell type transformers can be combined together to form

a 3-phase shell type unit. But some saving in iron can be achieved in constructing a single 3-

phase transformer. It does not differ from three 1-phase transformers put side by side. Saving in

iron is due to the joint use of magnetic paths between the coils. The three phases, in this case, are

more independent then they are in the core type transformers, because each phase has a magnetic

circuit independent of the other.

One main drawback in 3-phase transformer is that if any one phase becomes disabled,

then the whole transformer has to be ordinarily removed from service for repairs. However, in

the case of a 3-phase bank of 1-phase transformers if one transformer goes out of order, the

system can still be run open at reduced capacity or the faulty transformer can be readilyreplaced by a single spare.

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Three-phase transformer connections:

There are various methods available for transforming 3-phase voltages to higher or lower

3-phase voltages i.e. for handling a considerable amount of power. The most common

connections are

Y-Y

-

Y-

-Y

Open or V-V

Scott connection or T-T connectionBut here we are using only - and Y- as a bidirectional connections.

Delta-Delta or - connection

This connection is economical for large, low-voltage transformers in which insulation

problem is not so urgent, because it increases the number of turns per phase. The transformer

connections and voltage triangles. The ratio of transformation between primary and secondary

line voltage is exactly the same as that of each transformer. Further, the secondary voltage

triangle abc occupies the same relative position as the primary voltage triangle ABC i.e. there is

no angular displacement between the two. Moreover, there is no internal phase shift betweenphase and line voltages on either side as was the case in Y-Y connection. This connection has

following advantages

1. To make the output voltage sinusoidal it is necessary that the magnetizing currentof the transformer must contain a third harmonic component. So, third harmonic

component can flow in a delta connected transformer primaries without flowing

in the line wires. The three phases are 1200 apart which is 31200=3600 with

respect to the third harmonic component; hence it merely circulates in the delta.

Therefore, the flux is sinusoidal which results in sinusoidal voltages.

2. No difficulty is experienced from unbalanced loading as was the case in Y-Yconnection.

3. If the transformer becomes disabled the system can be continued to operate inopen Delta or V-V although with reduced available capacity.

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Wye/Delta or Y/ connection:The main use of this connection is at the sub-station end of the transmission line where

the voltage is to be stepped down. The primary winding is Y connected with grounded neutral.

The ratio between secondary and primary line voltage is 1/3 times the transformation ratio ofeach transformer. There is a 300 shift between the primary and its secondary line voltages which

means that Y- transformer bank cannot be paralleled with either a Y-Y or a - bank.

Instrument transformers:

To measure large currents & voltages in alternating circuits specially constructed

accurate ratio Instrument transformers are employed in conjunction with standard low range AC

instruments.

They are of two types

1. Current transformers &

2. Potential transformers

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Current transformers:

These transformers are used with low range ammeters to measure currents in high voltage

AC circuits. The current transformer has a primary coil of one or more turns of thick wire

connected in series with the line whose current is to be measured. The secondary consists of a

large number of turns of fine wire and is connected across the ammeter terminals.

Here the voltage stepped up and current is stepped down. One of the most commonly

used current transformers is known as Clamp ON or Clip ON type. Since the ammeter resistance

is very less the current transformer normally works short-circuited. If it is not done large amount

of primary flux will be setup .It damages insulation and core gets saturated.

Potential Transformers:

These transformers are extremely accurate ratio step down transformers and are used in

conjunction with standard low range voltmeters. They are of shell type transformers but there

power rating is extremely small. Up to voltages of 5000, potential transformers are usually of the

dry type, between 5000 & 13800 V they are always oil immersed type. For safety, the secondary

should be completely insulated from the high voltage primary and should be, in addition,

grounded for affording protection to operator.

Losses in a transformer:

In a static transformer there are no friction or windage losses hence the only losses

occurring are

1. Core Loss or Iron Loss

2. Copper Loss

Core or Iron Losses:

It includes both Hysteresis and eddy current losses. Because the core flux in a

transformer remains practically constant for all loads hence the core losses are constant.

Hysteresis losses occur due to application of varying strengths of AC and eddy current

losses occur due to the flow of currents in a closed path due to induced emf. These currents are

called as eddy currents.

Hysteresis Loss Wh = B1.6maxfv watt

Eddy Current loss We= PB2

maxf2t2 watts

Hysteresis losses can be minimized by using steel of high Si content for the core and

eddy current loss can be minimized by using very thin laminations. Iron Loss can be found from

Open Circuit Test. 27.


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Copper Losses:

This is due to the ohmic resistance of the transformer windings.

Total cu Losses = I12R1+I2

2R2 = I12R01 = I2

2R02

It is clear that Cu loss is proportional to (current) 2. The value of Cu losses can be found

by Short Circuit test.

The losses appear in the form of it and a drop in efficiency. Normally, the efficiency of

transformers is high about 99.5%.Cu loss inversely vary with Power Factor because current is

inversely proportional to power factor.

Cooling Methods:

To prevent rapid deterioration of the insulating materials inside a transformer, adequate

cooling of the windings and core must be provided.

Indoor transformers below 200kVA can be directly cooled by the natural flow of the

surrounding air. The metallic housing is fitted with ventilating louvers so that convection

currents may flow over the windings and around the core. Large transformers can be built the

same way, but forced circulation of clean air must be provided. Such dry type transformers are

used inside buildings, away from hostile atmospheres.

Distribution transformers below 200 kVA are usually immersed in mineral oil and

enclosed in a steel tank. Oil carries the heat away to the tank, where it is dissipated by radiation

and convection to the outside air. Oil is much better insulator than air is; consequently, it is

invariably used on high voltage transformers. As power rating increases, external radiators areadded to increase the cooling surface of the oil filled tank. Oil circulates around the transformer

windings and move through radiators, where the heat is again released to surrounding air. For

still higher ratings cooling fans blow air over the radiators. For the transformers in megawatt

range cooling may be affected by an oil water heat exchanger. Hot air drawn from the

transformer tank is pumped to a heat exchanger where it flows through pipes that are in contact

with cool water. Such a heat exchanger is very effective and costly.

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VARIABLE FREQUENCY DRIVE MOTORS

There are a wide range of motors ranging from 0.75kW to

500kW due to their cost and ability to perform under extremeconditions. With the continuing advances in power electronics and

microprocessor technology, AC variable speed drive has becomevery popular. With new technology, manufacturer with the use of

variable frequency drives can incorporate greater control, reduceswitching losses and provide greater power handling capability.

The motor used in a variable frequency drive system is usually a three-phase induction

motor. Some types of single-phase motors can be used, but three-phase motors are usually

preferred. Various types of synchronous motors offer advantages in some situations, butinduction motors are suitable for most purposes and are generally the most economical choice.

Motors that are designed for fixed-speed mains voltage operation are often used, but certain

enhancements to the standard motor designs offer higher reliability and better variable frequency

drive performance. A variable frequency drive system generally consists of an AC motor, acontroller and an operator interface.

Benefits of Variable Frequency Drives:

Increased Drive Efficiency (usually 97-98%) Reduced Volume and Weight Lower Price Reduced Audible Noise Level Improved Power Factor Reduced Harmonic Distortion to Supply

Improved Reliability Larger Voltage and Current Rating High Switching Speeds and lower Losses

Constant Torque Application:

Constant Torque applications are where the same amount of torque is required at low

speed as at high speed. Some applications may include conveyors, mixers, screw feeders,extruders and positive displacement pumps.

Constant Power Applications:

Constant power applications are where a high torque is required at low speed and a low

torque at high speed. Examples of applications are machine tools, tractions.

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Variable Torque Application

Variable torque is where a low torque is required at a low speed and higher torque at high

speed. Some applications are centrifugal loads such as fans, pumps and blowers. With theseapplications we will see the most energy saving by using a variable frequency drive.

Working

At the heart of an electric motor are the stator and the rotor. A magnetic field is generated

when a current is applied and the north/south field rotates through the stationary stator as the

rotor spins to catch up to the rotating field. The spinning of the rotor provides the torquenecessary to drive a load.

An electric motor turns at a given speed depending on the number of poles in the motor

and the frequency of the alternating current applied. Motor speed can be changed by changing

the alternating current frequency.

Nearly all variable frequency drives manufactured today are referred to as pulse width

modulation drives. These drives contain electronic circuitry that converts the 60 Hertz line power

to direct current, then pulses the output voltage for varying lengths of time to mimic an

alternating current at the frequency desired.

The use of variable frequency drive application is use majority for centrifugal pumps and

fans. The savings potential is the largest in these devices since the theoretical input power varies

with the cube of fan/pump speed and volume. A fan operating a half speed will require onlyabout 13 percent of full speed power. Losses in the variable frequency drive will reduce saving

somewhat, but the saving are still very impressive.

ELECTRO-STATIC PRECIPITATOR

The electro-static precipitator consists of metal plates which are electrically charged.

Dust and grit in the flue gases are attracted on to these plates, so that they do not pass up the

chimney to pollute the atmosphere. Regular mechanical hammer blows because theaccumulations of ash, dust and grit to fall to the bottom of the precipitator, where they collect in

a hopper for disposal Additional accumulations of ash also collect in hoppers beneath the

furnace.

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SCHEMATIC ARRANGEMENT OF THE PLANT


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Although steam power station simply involves the conversation of heat of bagasse into

electrical energy, it embraces many arrangements for proper working and efficiency. The whole

arrangement can be divided into the following stages for the sake of simplicity.

1. Fuel and ash handling arrangement

2. Steam generating plant

3. Steam turbine

4. Alternator

5. Feed water

6. Cooling arrangement

A. Fuel and ash handling arrangement

The bagasse coal is feed to the boiler by belt conveyers. The fuel is burnt in the boiler and the

ash produced after the complete combustion of bagasse is removed to the ash handling plant and

then delivered to the ash storage plant for disposal. The removal of the ash from the boiler

furnace is necessary for proper burning of fuel.

Here in this power generating station there is not much cost spent in purchasing the fuel. As

it is wastage of sugarcane left in sugar processing plant.

B. Steam generating plant

The Steam generating plant consists of a boiler for the production of steam and other

auxiliary equipment for the utilization of flue gases.

I. Boiler

The heat of combustion of bagasse in the boiler is utilized to convert water into a steam at

high pressure and temperature. The flue gases from the boiler make their journey through

superheater, economiser, air pre-heater and are finally exhausted to atmosphere though the

chimney.

The calorific value of the bagasse is 2400kCal/kg. The boiler is designed to produce 64 tonesof steam per hour at a temperature of 4150c and at a pressure of 42kg/cm2. The boiler

temperature is 14000c.

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II. Superheater

The steam produced in the boiler is wet and is passed through a superheater where it is dried

and is superheated. (Steam temperature increased above that of boiling point of water) the flue

gases on their way to chimney. Superheating provides two principle benefits. Firstly, the overall

efficiency is increased. Secondly, too much condensation in the last stages of turbine (whichwould cause blade corrosion) is avoided. The superheated steam from the superheater is fed to

steam turbine through the main valve.

III. Economiser

An economiser is essentially a feed water heater and derives heat from the flue gases for this

purpose. The feed water is fed to the economiser before supplying to the boiler. The economiser

extracts a part of heat of flue gases to increase the feed water temperature.

IV. Air-preheater

An air-preheater increase the temperature of the air supplied for bagasse burning by deriving

heat from the flue gases. Air is drawn from the atmosphere by forced draught fan and is passed

through air-preheater before supplying to the boiler furnace. The air-preheater extracts heat from

flue gases and increases the temperature of air used for bagasse combustion. The principle

benefits of preheating the air are:

Increased thermal efficiency

Increased steam capacity per square meter of boiler surface

In KBD sugars the forced draught fan is 75Hp and is one in number.

C. Steam turbine

The dry and superheated steam from the superheater is fed to the steam turbine through main

valve. The heat energy of steam when passing over the blades of turbine is the converted into

mechanical energy. After giving heat energy to the turbine, the steam is exhausted to the

condenser which condenses the exhausted steam by means of cold water circulation. The

governor mechanism is employed to control the fuel falling into the boiler. The speed of the

steam impulse turbine is 8250rpm.

D. Alternator

The steam turbine is coupled to an alternator. The alternator converts mechanical energy of

turbine into electrical energy. The electrical output from the alternator is delivered to the bus bars

through transformer, circuit breakers and isolators.

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The alternator rotates with the 1500rpm delivers the 6MW output at a voltage of 11Kv.

The steam turbine is coupled to the alternator by means of reduction gear box. The reduction

gear box reduces the speed to be matched with the alternator.

E. Feed water

The condensate from the condenser is used as feed water to the boiler. Some water may be

lost in the cycle which is suitably made up from external sources. The feed water on its way to

the boiler is heated by the water heaters and economizer. This help in rising overall efficiency of

the plant.

F. Cooling arrangement

In order to improve the efficiency of the plant, the steam exhausted from the turbine is

condensed by means of condenser. Water is drawn from a bore well and is circulated through the

condenser. The circulating water takes up the heat of exhausted steam and itself become hot.Since the water availability is less, cooling towers are used. Hot water from the condenser is

passed on the cooling towers where it is cooled. The cold water from the cooling towers is

residue in the condenser.

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The survival of industrial undertakings and our social structures depends primarily upon

low cost and interrupted supply of electrical energy. In fact, the advancement of country is

measured in terms of per capita consumption of electrical energy.

The conversion of energy available in different forms in nature into electrical energy is

known asgeneration of electrical energy.

Energy is available in various forms from different natural sources such as pressure head

of water, chemical energy of fuels, nuclear energy of radioactive substances etc.

All these forms of energy can be converted into electrical energy by the use of suitable

arrangement. In this project we studied that the production of electrical energy from the wastage

of sugar cane i.e., bagasse.

The arrangement essentially employs an alternator coupled to a prime mover. The prime

mover is driven by the energy obtained from burning of bagasse. Heat energy of bagasse can be

used to produce steam at high temperature and pressure.

The steam is fed to steam turbine. The turbine converts heat energy of steam into

mechanical energy which is further converted into electrical energy by the alternator. The energy

produced is utilized for the operation the industrial plant.

CONCLUSION


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BIBLIOGRAPHY

1. PRINCIPLES OF POWER SYSTEM - V.K. MEHTA

2. ELECTRICAL POWER - C.L. WARDHWA

3. ELECTRICAL POWER - J.B. GUPTHA

4. ELECTRICAL TECHNOLOGY -B.L.THERAJA

A.K.THERAJA

Co-generation Power Plant.

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Transcript of Co-generation Power Plant.