1

Sources of Energy: The followings are the various sources of energy:

1) The Sun (2) The Wind (3) Water (4) Fuels (5) Nuclear

Energy

1. The Sun: The Sun is the primary source of energy. The heat energy

radiated by the Sun can be focused over a small area by means of reflectors.

This heat can be used to raise steam and electrical energy can be produced

with the help of turbine-alternator combination. However, this method has

limited application because:

(a) It requires a large area for the generation of even a small amount of

electric power

(b) It cannot be used in cloudy days or at night

(c) It is an uneconomical method.

Nevertheless, there are some locations in the world where strong

solar radiation is received very regularly and the sources of mineral

fuel are scanty or lacking. Such locations offer more interest to the

solar plant builders.

(ii) The Wind: This method can be used where wind flows for a

considerable length of time. The wind energy is used to run the wind

mill which drives a small generator. In order to obtain the electrical

energy from a wind mill continuously, the generator is arranged to

charge the batteries. These batteries supply the energy when the

wind stops. This method has the advantages that maintenance

and generation costs are negligible. However, the drawbacks of

this method are (a) variable output, (b) unreliable because of

uncertainty about wind pressure and (c) power generated is quite

small.

(iii) Water: When water is stored at a suitable place, it possesses

potential energy because of the head created. This water energy can

be converted into mechanical energy with the help of water turbines.

The water turbine drives the alternator which converts mechanical

energy into electrical energy. This method of generation of electrical

energy has become very popular because it has low production and

maintenance costs.

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(iv) Fuels: The main sources of energy are fuels viz., solid fuel as

coal, liquid fuel as oil and gas fuel as natural gas. The heat energy of

these fuels is converted into mechanical energy by suitable prime

movers such as steam engines, steam turbines, internal combustion

engines etc. The prime mover drives the alternator which converts

mechanical energy into electrical energy. Although fuels continue to

enjoy the place of chief source for the generation of electrical energy,

yet their reserves are diminishing day by day. Therefore, the present

trend is to harness water power which is more or less a permanent

source of power.

(v) Nuclear energy: Towards the end of Second World War, it was

discovered that large amount of heat energy is liberated by the fission

of uranium and other fissionable materials. It is estimated that heat

produced by 1 kg of nuclear fuel is equal to that produced by 4500

tonnes of coal. The heat produced due to nuclear fission can be

utilized to raise steam with suitable arrangements. The steam can run

the steam turbine which in turn can drive the alternator to produce

electrical energy. However, there are some difficulties in the use of

nuclear energy. The principal ones are (a) high cost of nuclear plant

(b) problem of disposal of radioactive waste and dearth of trained

personnel to handle the plant.

3

Reason for present energy crisis all around the world:

The followings are main reasons for present energy crisis all around the world.

1. Overconsumption: The energy crisis is a result of many different strains

on our natural resources, not just one.

2. Overpopulation: Another cause of the crisis has been the steady increase

in the world’s population and its demands for fuel and products.

3. Poor Infrastructure: Most of the energy producing firms keeps on using

outdated equipment that restricts the production of energy.

4. Unexplored Renewable Energy Options: Renewable energy still remains

unused are most of the countries.

5. Delay in Commissioning of Power Plants: In few countries, there is a

significant delay in commissioning of new power plants that can fill the gap

between demand and supply of energy. The result is that old plants come

under huge stress to meet the daily demand for power. When supply don’t

matches demand, hence results in load shedding and breakdown.

6. Wastage of Energy: In most parts of the world, people do not realize the

importance of conserving energy.

7. Poor Distribution System: Frequent tripping and breakdown are result of

a poor distribution system.

8. Major Accidents and Natural Calamities: Major accidents like pipeline

burst and natural calamities like eruption of volcanoes, floods, earthquakes

can also cause interruptions to energy supplies.

4

Types of Dams used in Hydro-electric power station:

Based on the functions of dams:

Storage dams: They are constructed to store water during the rainy season

when there is a large flow in the river.

Diversion dams: A diversion dam is constructed for the purpose of diverting

water of the river into an off-taking canal (or a conduit). They provide sufficient

pressure for pushing water into ditches, canals, or other conveyance systems.

Detention dams: Detention dams are constructed for flood control. A detention

dam retards the flow in the river on its downstream during floods by storing

some flood water.

Debris dams: A debris dam is constructed to retain debris such as sand, gravel,

and drift wood flowing in the river with water. The water after passing over a

debris dam is relatively clear.

Based on structure and design:

Gravity Dam: A gravity dam is a dam constructed from concrete or stone

masonry and designed to hold back water by utilizing the weight of the material

alone to resist the horizontal pressure of water pushing against it. Gravity dams

are designed so that each section of the dam is stable, independent of any other

dam section.

Gravity dam resist water pressure, uplift pressure, pressure due to earthquake, silt pressure, wave pressure, ice pressure. Gravity Dam maybe: Straight gravity dam – It is straight in plan. Curved gravity plan – It curved in plan. Curved gravity dam (Arch gravity dam) – It resists the forces acting on it by combined gravity action (its own weight) and arch action. Solid gravity dam – Its body consists of a solid mass of masonry or concrete Hollow gravity dam – It has hollow spaces within its body. Earth Dams: An earth dam is made of earth (or soil) built up by compacting successive layers of earth. Earth dam resists the forces exerted upon it mainly due to shear strength of the soil. Examples of earthfill dam: Rongunsky dam (Russia) and New Cornelia Dam (USA).

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Rockfill Dams: A rockfill dam is built of rock fragments and boulders of large size. An impervious membrane is placed on the rockfill on the upstream side to reduce the seepage through the dam. The membrane is usually made of cement concrete or asphaltic concrete. The side slopes of rockfill are usually kept equal to the angle of repose of rock, which is usually taken as 1.4:1 (or 1.3:1). Rockfill dams require foundation stronger than those for earth dams. Examples of rockfill dam: Mica Dam (Canada) and Chicoasen Dam (Mexico). Arch Dams: An arch dam is curved in plan, with its convexity towards the

upstream side. They transfer the water pressure and other forces mainly to the

abutments by arch action. An arch dam is quite suitable for narrow canyons with

strong flanks which are capable of resisting the thrust produced by the arch

action. The section of an arch dam is approximately triangular like a gravity dam

but the section is comparatively thinner. The arch dam may have a single

curvature or double curvature in the vertical plane. Generally, the arch dams of

double curvature are more economical and are used in practice. Examples of

Arch dam: Hoover Dam (USA) and Idukki Dam (India).

Uttress Dams: Buttress dams are of three types: (i) Deck type, (ii) Multiple-arch

type, and (iii) Massive-head type.

Buttress Dam: A buttress dam is a dam with a solid, water-tight upstream side

that is supported at intervals on the downstream side by a series

of buttresses or supports. The dam wall may be straight or curved. Most

buttress dams are made of reinforced concrete and are heavy, pushing the dam

into the ground. Water pushes against the dam, but the buttresses are inflexible

and prevent the dam from falling over.

Steel Dams: Dams: A steel dam consists of a steel framework, with a steel skin

plate on its upstream face, rather than the more

common masonry, earthworks, concrete or timber construction materials.

Timber Dams: Main load-carrying structural elements of timber dam are made

of wood, primarily coniferous varieties such as pine and fir.

Rubber Dams: A symbol of sophistication and simple and efficient design, this

most recent type of dam uses huge cylindrical shells made of special synthetic

rubber and inflated by either compressed air or pressurized water. Rubber dams

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offer ease of construction, operation and decommissioning in tight schedules.

These can be deflated when pressure is released.

Principle of working of thermal power plant:

A thermal power plant basically operates on the Rankine cycle. Coal is burnt in

a boiler, which converts water into steam. The steam is expanded in a turbine,

which produces mechanical power driving the alternator coupled to the turbine.

The steam after expansion in prime mover (turbine) is usually condensed in a

condenser to be fed into the boiler again.

The working of modern coal-fired thermal power plant can be studied

conveniently with the help of various cycles. The entire arrangement for sake of

simplicity may be divided into four main circuits namely

(i) Fuel and ash circuit (ii) Air and fuel gas circuit (iii) Feed water and steam

circuit and (iv) Cooling water circuit.

(i) Coal and Ash Circuit: In this circuit, the coal from the storage is fed to the boiler through coal handling equipment for the generation of steam. Ash produced due to combustion of coal is removed to ash storage through ash-handling system.

(ii) Air and Gas Circuit: Air is supplied to the combustion chamber of the boiler either through forced draught or induced draught fan or by using both. The dust from the air is removed before supplying to the combustion chamber. The

7

exhaust gases carrying sufficient quantity of heat and ash are passed through the air-heater where the exhaust heat of the gases is given to the air and then it is passed through the dust collectors where most of the dust is removed before exhausting the gases to the atmosphere.

(iii) Feed Water and Steam Circuit: The steam generated in the boiler is fed to the steam prime mover to develop the power. The steam coming out of the prime mover is condensed in the condenser and then fed to the boiler with the help of pump. The condensate is heated in the feed-heaters using the steam tapped from different points of the turbine. The feed heaters may be of mixed type or indirect heating type. Some of the steam and water are lost passing through different components of the system, therefore, feed water is supplied from external source to compensate this loss. The feed water supplied from external source to compensate the loss. The feed water supplied from external source is passed through the purifying plant to reduce to reduce dissolve salts to an acceptable level. This purification is necessary to avoid the scaling of the boiler tubes.

(iv) Cooling Water Circuit: The quantity of cooling water required to condense the steam is considerably high and it is taken from a lake, river or sea. At the Columbia thermal power plant it is taken from an artificial lake created near the plant. The water is pumped in by means of pumps and the hot water after condensing the steam is cooled before sending back into the pond by means of cooling towers. This is done when there is not adequate natural water available close to the power plant. This is a closed system where the water goes to the pond and is re circulated back into the power plant. Generally open systems like rivers are more economical than closed systems.

8

Choice of site and other geographical arrangements for hydro-electric

plant:

(i) Availability of water: Since the primary requirement of a hydro-

electric power station is the availability of huge quantity of water, such

plants should be built at a place (e.g., river, canal) where adequate

water is available at a good head.

(ii) Storage of water: There are wide variations in water supply from a

river or canal during the year. This makes it necessary to store water by

constructing a dam in order to ensure the generation of power

throughout the year. The storage helps in equalising the flow of water so

that any excess quantity of water at a certain period of the year can be

made available during times of very low flow in the river. This leads to

the conclusion that site selected for a hydro-electric plant should provide

adequate facilities for erecting a dam and storage of water.

(iii) Cost and type of land: The land for the construction of the plant

should be available at a reasonable price. Further, the bearing capacity

of the ground should be adequate to with- stand the weight of heavy

equipment to be installed.

(iv) Transportation facilities: The site selected for a hydro-electric

plant should be accessible by rail and road so that necessary equipment

and machinery could be easily transported.

(v) Water pollution: Polluted water may cause excessive corrosion and

damage to metallic structures. This may render the operation of the plant

unreliable and uneconomic.

(vi) Geological Investigation: Geological investigations are needed to see

that the foundation rock for the dam and other structure is firm, stable,

impervious and strong enough to withstand water thrust and other stresses.

(vii) Earthquakes and Seismicity: The area should be free from earthquakes.

(vii) High average rain fall: The Dam should be selected at that place where

there should be high average rain fall.

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Various types of power plants and its efficiencies:

Efficiencies Thermal power plant

Hydro power plant

Diesel Power Plant

Nuclear power plant

Overall Efficiency

Least efficient

Most Efficient

More efficient than thermal power plant

More efficient than thermal power plant

overall efficiency is about 25%

Overall efficiency is about 85%

Efficiency is about 35%

Efficiency is in the range of 38%

Principle of working of hydroelectric power plant:

In hydroelectric power plants the potential energy of water due to its high

location is converted into electrical energy. The total power generation capacity

of the hydroelectric power plants depends on the head of water and volume of

water flowing towards the water turbine. The dam is built across the large river

that has sufficient quantity of water throughout the river. In certain cases where

the river is very large, more than one dam can built across the river at different

locations.

The water flowing in the river possesses two type of energy:

(1) The kinetic energy due to flow of water and

(2) Potential energy due to the height of water.

In hydroelectric power and potential energy of water is utilized to generate

electricity.

More the head of water more is the power produced in the hydroelectric power

plant. To obtain the high head of water the reservoir of water should as high as

possible and power generation unit should be as low as possible. The

maximum height of reservoir of water is fixed by natural factors like the height of

river bed, the amount of water and other environmental factors. The location of

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the power generation unit can be adjusted as per the total amount of power that

is to be generated. Usually the power generation unit is constructed at levels

lower than ground level so as to get the maximum head of water. The total flow

rate of water can be adjusted through the pen stock as per the requirements. If

more power is to be generated more water can be allowed to flow through it.

Turbine:

A turbine is a machine which converts rotational energy from fluids into

mechanical energy of a rotating shaft which drives an alternator.

Types of Turbines:

1. Steam turbines: Most power plants use coal, natural gas, oil or a nuclear

reactor to create steam. The steam runs through a huge and very carefully

designed multi-stage turbine to spin an output shaft that drives the plant's

generator.

2. Gas turbines: A gas turbine, also called a combustion turbine, is a type

of internal combustion engine. It has an upstream

rotating compressor coupled to a downstream turbine, and a combustion

chamber in between.

3. Transonic turbine: The gas flow in most turbines employed in gas turbine

engines remains subsonic throughout the expansion process. In a

transonic turbine the gas flow becomes supersonic as it exits the nozzle

guide vanes, although the downstream velocities normally become

subsonic. Transonic turbines operate at a higher pressure ratio than

normal but are usually less efficient and uncommon.

4. Contra-rotating turbines: A contra-rotating steam turbine, usually known as

the Ljungström turbine. he design is essentially a multi-stage radial turbine

offering great efficiency, four times as large heat drop per stage as in the

reaction turbine, extremely compact design and the type met particular

success in back pressure power plants.

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5. Ceramic turbine: Conventional high-pressure turbine blades are made from

nickel based alloys and often utilise intricate internal air-cooling passages

to prevent the metal from overheating. In recent years, experimental

ceramic blades have been manufactured and tested in gas turbines, with a

view to increasing rotor inlet temperatures and possibly, eliminating air

cooling.

6. Shrouded turbine: Many turbine rotor blades have shrouding at the top,

which interlocks with that of adjacent blades, to increase damping and

thereby reduce blade flutter. In large land-based electricity generation

steam turbines, the shrouding is often complemented, especially in the

long blades of a low-pressure turbine, with lacing wires. These wires pass

through holes drilled in the blades at suitable distances from the blade root

and are usually brazed to the blades at the point where they pass through.

Lacing wires reduce blade flutter in the central part of the blades. The

introduction of lacing wires substantially reduces the instances of blade

failure in large or low-pressure turbines.

7. Bladeless turbine: It uses the boundary layer effect and not a fluid

impinging upon the blades as in a conventional turbine.

8. Water turbines:

a. Pelton turbine, a type of impulse water turbine.

b. Francis turbine, a type of widely used water turbine.

c. Kaplan turbine, a variation of the Francis Turbine.

d. Turgo turbine, a modified form of the Pelton wheel.

e. Cross-flow turbine, also known as Banki-Michell turbine, or Ossberger turbine.

9. Wind turbine: These normally operate as a single stage without nozzle and

interstage guide vanes. An exception is the Éolienne Bollée, which has a

stator and a rotor.

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Operation of Electric Arc Furnace:

The scrap is charged commonly from the furnace top.

The roof with the electrodes is swung aside before the scrap charging.

The scrap arranged in the charge basket is transferred to the furnace by a

crane and then dropped into the shell.

Lower voltages are selected for this first part of the operation to protect the

roof and walls from excessive heat and damage from the arcs.

Once the electrodes have reached the heavy melt at the base of the

furnace and the arcs are shielded by the scrap.

The voltage can be increased and the electrodes raised slightly,

lengthening the arcs and increase power to the melt.

Water softening and ash handling in thermal power station:

Water softening in thermal power station:

It is used to remove impurities like suspended particles, minerals and biological

impurities.

Equipment for demineralization cum softening plant consists of two streams

each stream with activated carbon filter, acid, cation exchanger and mixed bed

exchanger.

It is done when hardness alone is a limiting factor

In thermal power station soluble water impurities are removed with the help

of PAC (Poly Aluminum Chloride)

And cation-exchange zeolite resin exchanges all hardness ions to reduce

hardness to zero

Ash handling in thermal Power Station:

Ash handling refers to the method of collection, conveying, interim storage and

load out of various types of ash residue left over from solid fuel combustion

processes. The most common types of ash include bottom ash, bed ash, fly ash

and ash clinkers resulting from the combustion of coal, wood and other solid

13

fuels. Ash handling systems may employ pneumatic ash conveying or

mechanical ash conveyors. Electrostatic Precipitator is used in ash handling

plant to remove fly ash.

Parts of Ash Handling System:

Bottom Ash Handling System

Coarse Ash (Economizer Ash) handling system

Air Pre Heater ash handling system

Fly ash handling system

Ash slurry disposal system

Use of ash:

Manufacturing of building materials.

Making of concrete.

Manufacturing of cement.

Road construction etc.

Types of Loads:

A device which taps electrical energy from the electric power system is

called a load on the system. The load may be resistive (e.g., electric

lamp), inductive (e.g., induction motor), capacitive or some combination

of them. The various types of loads on the power system are:

(i) Domestic load. Domestic load consists of lights, fans, refrigerators,

heaters, television, small motors for pumping water etc. Most of the

residential load occurs only for some hours during the day (i.e., 24

hours) e.g., lighting load occurs during night time and domestic appliance

load occurs for only a few hours. For this reason, the load factor is low

(10% to 12%).

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(ii) Commercial load. Commercial load consists of lighting for shops,

fans and electric appliances used in restaurants etc. This class of load

occurs for more hours during the day as compared to the domestic load.

The commercial load has seasonal variations due to the extensive use

of air- conditioners and space heaters.

(iii) Industrial load. Industrial load consists of load demand by

industries. The magnitude of industrial load depends upon the type of

industry. Thus small scale industry requires load upto 25 kW, medium

scale industry between 25kW and 100 kW and large-scale industry

requires load above 500 kW. Industrial loads are generally not weather

dependent.

(iv) Municipal load. Municipal load consists of street lighting, power

required for water sup- ply and drainage purposes. Street lighting load

is practically constant throughout the hours of the night. For water

supply, water is pumped to overhead tanks by pumps driven by electric

motors. Pumping is carried out during the off-peak period, usually

occurring during the night. This helps to improve the load factor of the

power system.

(v) Irrigation load. This type of load is the electric power needed for

pumps driven by motors to supply water to fields. Generally this type of

load is supplied for 12 hours during night.

(vi) Traction load. This type of load includes tram cars, trolley buses, railways

etc. This class of load has wide variation. During the morning hour, it reaches

peak value because people have to go to their work place. After morning hours,

the load starts decreasing and again rises during evening since the people start

coming to their homes.

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Four cycles for the principle of working of Diesel engine:

These are the followings:

1. Intake: In this cycle the piston begins at top dead center. The piston descends from the top of the cylinder to the bottom of the cylinder, increasing the volume of the cylinder. A mixture of fuel and air is forced by atmospheric (or greater by some form of air pump) pressure into the cylinder through the intake port.

2. Compression: with both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the air or fuel-air mixture into the cylinder head.

3. Power: this is the start of the second revolution of the cycle. While the piston is close to Top Dead Centre, the compressed air–fuel mixture in a gasoline engine is ignited, by a spark plug in gasoline engines, or which ignites due to the heat generated by compression in a diesel engine. The resulting pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward bottom dead centre.

4. Exhaust: during the exhaust stroke, the piston once again returns to top dead centre while the exhaust valve is open. This action expels the spent fuel-air mixture through the exhaust valve(s).

Factors to be considered in deciding the location of nuclear reactor and

nuclear power plant:

The following points should be kept in view while selecting the site for a nuclear

power station :

(i) Availability of water. As sufficient water is required for cooling

purposes, therefore, the plant site should be located where ample

quantity of water is available, e.g., across a river or by sea-side.

(ii) Disposal of waste. The waste produced by fission in a nuclear

power station is generally radioactive which must be disposed off

properly to avoid health hazards. The waste should either be buried in a

deep trench or disposed off in sea quite away from the sea shore.

Therefore, the site selected for such a plant should have adequate

arrangement for the dis- posal of radioactive waste.

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(iii) Distance from populated areas. The site selected for a nuclear

power station should be quite away from the populated areas as there is

a danger of presence of radioactivity in the atmosphere near the plant.

However, as a precautionary measure, a dome is used in the plant which

does not allow the radioactivity to spread by wind or underground

waterways.

(iv) Transportation facilities. The site selected for a nuclear power

station should have adequate facilities in order to transport the heavy

equipment during erection and to facilitate the move- ment of the workers

employed in the plant.

(v) Security and Safety: The security to protect atomic material from

terrorist.

(vii) Seismic and Geologic Sitting Criteria: The location nature according investigations should be free from geologic and seismic problems which are necessary to determine site suitability and to provide reasonable assurance.

From the above mentioned factors it becomes apparent that ideal

choice for a nuclear power station would be near sea or river and away

from thickly populated areas.

Method used for earthing the power system neutral:

There are the followings

methods for Neutral earthing:

1. Underground Neutral Earthing System: In ungrounded system there is no internal connection between the conductors and earth. However, as system, a capacitive coupling exists between the system conductors and the adjacent grounded

17

surfaces. Consequently, the “ungrounded system” is, in reality, a “capacitive grounded system” by virtue of the distributed capacitance. Under normal operating conditions, this distributed capacitance causes no problems. In fact, it is beneficial because it establishes, in effect, a neutral point for the system; As a result, the phase conductors are stressed at only line-to-neutral voltage above ground. But problems can rise in ground fault conditions. A ground fault on one line results in full line-to-line voltage appearing throughout the system. Thus, a voltage 1.73 times the normal voltage is present on all insulation in the system. This situation can often cause failures in older motors and transformers, due to insulation breakdown.

2. Solid Neutral Earthed System: “When the neutral point of a 3-phase system (e.g. 3-phase generator,3-phase transformer etc.) is directly connected to earth (i.e. soil) through a wire of negligible resistance and reactance, it is called solid grounding or effective grounding.”

In this method neutral point is always grounded.

3. Resistance Neutral Earthing System: When the neutral point of a 3-phase system (e.g. 3-phase generator, 3-phase transformer etc.) is connected to earth (i.e. soil) through a resistor, it is called resistance grounding.

Fig. Shows the grounding of neutral point through a resistor R.

The value of R should neither be very low nor very high. If the value of earthing resistance R is very low, the earth fault

current will be large and the system becomes similar to the solid grounding system.

On the other hand, if the earthing resistance R is very high, the system conditions become similar to ungrounded System.

The value of R is so chosen such that the earth fault current is limited to safe value but still sufficient to permit the operation of earth fault protection system.

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In practice, that value of R is selected that limits the earth fault current to 2 times the nor-mal full load current of the earthed generator or transformer.

4. Resonant Neutral Earthing

System: When the value of L of arc suppression coil is such that the fault current IF exactly balances the capacitive current IC, it is called resonant grounding. An arc suppression coil (also called Peterson coil) is an iron-cored coil connected between the neutral and earth as shown in Fig. The reactor is provided with tapings to change the inductance of the coil. By adjusting the tapings on the coil, resonant grounding can be achieved.

Load factor. The ratio of average load to the maximum demand during a given

period is known as load factor i.e.

Load factor = Average load

Max.demand

If the plant is in operation for T hours,

Load factor = Average load x T

Max.demand x T

Load factor = Units generated in T hours

Max.demand x T hours

The load factor may be daily load factor, monthly load factor or annual

load factor if the time period considered is a day or month or year. Load

factor is always less than 1 because average load is smaller than the

maximum demand. The load factor plays key role in determining the

overall cost per unit generated. Higher the load factor of the power

station, lesser* will be the cost per unit generated.

Diversity Factor: The ratio of the sum of individual maximum

demands to the maximum demand on power station is known as

diversity factor i.e.

Diversity factor = Sum of individual max.demands

Max.demand on power station

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A power station supplies load to various types of consumers whose maximum

demands generally do not occur at the same time. Therefore, the maximum

demand on the power station is always less than the sum of individual maximum

demands of the consumers. Obviously, diversity† factor will always be greater

than 1. The greater the diversity factor, the lesser‡ is the cost of generation of

power.

Effect of load factor on cost of energy:

Load factor affects the cost of energy. Higher the load factor, higher will be the

average load. So, No. of units generated for a given period of time for the same

max. demand will be more. Therefore, overall cost per unit of electrical energy

decreases due to distribution of standing charges which are proportional to the

max. demand and independent of units generated.

Diversity factor affects the cost of energy. More is the diversity lesser will be

max. demand due to which installation capacity of plant will be less. Lesser is

the installation capacity lesser will be the capital required for installation. So

lesser will be generation cost. And the fixed charges in the tariff would be less.

Connected load: It is the sum of continuous ratings of all the

equipment’s connected to supply system.

A power station supplies load to thousands of consumers. Each

consumer has certain equipment installed in his premises. The sum of

the continuous ratings of all the equipment’s in the consumer’s premises

is the “connected load” of the consumer. For instance, if a consumer has

connections of five 100-watt lamps and a power point of 500 watts, then

connected load of the consumer is 5 x 100 + 500 = 1000 watts. The sum

of the connected loads of all the consumers is the connected load to the

power station.

Maximum demand: It is the greatest demand of load on the power

station during a given period.

The load on the power station varies from time to time. The maximum of

all the demands that have occurred during a given period (say a day) is

the maximum demand. Thus referring back to the load curve of Fig. 3.2,

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the maximum demand on the power station during the day is 6 MW and

it occurs at 6 P.M. Maximum demand is generally less than the

connected load because all the consumers do not switch on their

connected load to the system at a time. The knowledge of maxi- mum

demand is very important as it helps in determining the installed capacity

of the station. The station must be capable of meeting the maximum

demand.

Demand factor. It is the ratio of maximum demand on the power station

to its connected load i.e.

Demand factor = Maximum demand

connected load

The value of demand factor is usually less than 1. It is expected

because maximum demand on the power station is generally less than

the connected load. If the maximum demand on the power station is 80

MW and the connected load is 100 MW, then demand factor = 80/100 =

0·8. The knowledge of demand factor is vital in determining the capacity

of the plant equipment.

Comparison of Hydro and diesel electric station:

Hydroelectric power

station

Diesel electric power

station

Initial cost is very high Initial cost is very low

Running cost is zero, as it

use water which is for free

Running cost is high, as it

use diesel which is not for

free

Power availability may be

affected by seasonal

precipitation

There is no seasonal

precipitation in diesel electric

power station

It does not make pollution in

the environment

It creates pollution in the

environment

In this station water is

renewable fuel source

In this station diesel is non-

renewable source

Require large space Require less space as

compared to hydro power

station

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Comparison of Boiling water reactor and pressurized water

nuclear reactor:

Boiling water reactor Pressurized water nuclear

reactor

The steam in boiling water

reactor is produced directly

in the reactor core

While the steam in a

pressurized water reactor is

produced in a secondary

system

The pressure of a boiling

water reactor remains

constant which is 1040 psi,

The pressure of a

pressurized boiling reactor

varies from the primary

system to the output steam,

2250 psi then lowered

the steam in a boiling water

reactor, after coming out of

the steam separators,

proceeds to a steam dryer

and then to the turbine

The steam in a pressurized

water reactor after coming

out of the steam separator

proceeds directly to the

turbine

The water is allowed to boil Preventing the water from

actually boiling.

The steam produced in a

boiling water reactor is

radioactive

Whereas the steam

produced in pressurized

water reactor is

nonradioactive.

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Operation of nuclear power reactor and its control:

The operation of nuclear power reactor is based on nuclear fission

reaction, 235U fissions by absorbing a neutron and producing 2 to 3

neutrons, which initiate on average one more fission to make a

controlled chain reaction

Normal water is used as a moderator to slow the neutrons since

slow neutrons take longer to pass by a U nucleus and have more

time to be absorbed

The protons in the hydrogen in the water have the same mass as

the neutron and stop them by a billiard ball effect

The extra neutrons are taken up by protons to form deuterons

235U is enriched from its 0.7% in nature to about 3% to produce the

reaction, and is contained in rods in the water

Boron control rods are inserted to absorb neutrons when it is time

to shut down the reactor

The hot water is boiled or sent through a heat exchanger to

produce steam. The steam then powers turbines.

Nuclear power reactor can be controlled with control-rods - these are

dense materials which, when dropped down into the reactor, soak up

some of the neutrons that are produced by the nuclear chain

reaction. The consequence of that is that there are fewer neutrons left

to bust open other uranium or fissionable nuclei, and as a result, the

chain reaction is slowed down. By putting the fuel rods in, or drawing

them out, you can speed up or slow down the chain reaction, and

therefore, you can affect how much energy actually comes out of the

reactor.

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Importance of Wind Energy:

The importance of wind energy is given below:

1) Wind energy is always for free and can be used without any cost.

2) Wind energy is a form of energy which is pollution free and eco-

friendly. It does not release any harmful emissions or pollutants

that enter the atmosphere from using them.

3) It acts as a great way to supply electricity to rural areas.

4) Wind energy is home grown, and local landowners and small

businesses can operate single turbines or clusters of turbines.

5) Wind energy is a renewable resource that can be used forever, as

long as there is wind.

6) Wind energy is the best alternate to the traditional methods of

generating power.

7) Wind is considered a native fuel that does not need to be

transported.

8) Wind energy requires small area of land.

Energy resources: An energy resource is something that can produce heat,

power life, move objects, or produce electricity. Material such as coal, gas, oil,

and wood consumed in generation of power.

Difference between renewable and non-renewable energy resources:

renewable resources Non-renewable resources

Resources that can be

replenished naturally in the

course of time are called

renewable resources.

Nonrenewable resources cannot

be replenished.

It can be used again and again. It can be used once.

We have unlimited supplies of

them.

We have limited supplies of

them, and when these supplies

are gone we will not have any

more.

It is environmental friendly. It makes pollution

Examples: air, water, sunlight,

wind, rain, tides, bio-fuel,

geothermal energy.

Examples: coal, Natural gas, oil,

nuclear fuels

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Fossil fuel: Fuels formed by natural resources such as anaerobic

decomposition of buried dead organisms. Fossil fuels are the carbon

rich remains of ancient vegetation and other organisms that have

endured intense heat and pressure inside the earth, the age of the

organisms and their resulting fossil fuels is typically millions of years,

but exceeds 2 billion years.

Different types of fossil fuels are: coal, petroleum and natural gas.

Layout of hydroelectric power plant:

:

Examples:

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List of all types of hydroelectric power plant:

1) Water wheels

2) Hydro power plants

3) Wave energy from oceans

4) Tidal energy

5) Damless hydro power

Based on Quantity of Water Available

1) Run-off river hydro plants with pondage

2) Run-off river hydro plants without pondage

3) Reservoir hydroelectric power plants

Based on the Head of Water Available

1) Low head hydroelectric power plants

2)Medium head hydroelectric power plants

3) High head hydroelectric power plants

Based on the Nature of Load

1) Base load hydroelectric power plants

2) Peak load hydroelectric power plants

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Difference between Impulse(Pelton) wheel and Reaction (Francis,

Kaplan and Propeller) Turbine

Impulse turbine Reaction turbine

Impulse Turbine operates at high

water heads.

Reaction turbine operate at low

and medium heads.

In Impulse Turbine all hydraulic

energy is converted into kinetic

energy by a nozzle and it is is

the jet so produced which strikes

the runner blades.

In Reaction Turbine only some

amount of the available energy is

converted into kinetic energy

before the fluid enters the

runner.

Water is admitted only in the

form of jets. There may be one

or more jets striking equal

number of buckets

simultaneously.

Water is admitted over the entire

circumference of the runner.

The turbine doesn’t run full and

air has a free access to the

bucket.

Water completely fills at the

passages between the blades

and while flowing between inlet

and outlet sections does work on

the blades.

The turbine is always installed

above the tail race and there is

no draft tube used.

Reaction turbine are generally

connected to the tail race

through a draft tube which is a

gradually expanding passage. It

may be installed below or above

the tail race.

Flow regulation is done by

means of a needle valve fitted

into the nozzle.

The flow regulation in reaction

turbine is carried out by means

of a guide-vane assembly. Other

component parts are scroll

casing, stay ring runner and the

draft tub.

Impulse Turbine have more

hydraulic efficiency.

Reaction Turbine have relatively

less efficiency.

Impulse turbine involves less

maintenance work.

Reaction turbine involves more

maintenance work.

Water flow is tangential direction

to the turbine wheel.

Water flows in radial(Francis)l

and axial(Kaplan) direction to

turbine wheel.

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Difference between Kaplan turbine and Francis turbine:

Kaplan Turbine Francis Turbine

Water enters the runner

vanes axially and leave

axially hence it is called axial

flow turbine.

Water enters the runner

vanes radially and leaves

axially hence it is called a

mixed flow turbine.

The number of blades in the

runner is generally between

3 and 8.

The number of blades in the

runner is generally between

16 and 24.

Advantages and disadvantages of hydroelectric power plant:

Advantages:

(i) It requires no fuel as water is used for the generation of electrical

energy.

(ii) It is quite neat and clean as no smoke or ash is produced.

(iii) It requires very small running charges because water is the source

of energy which is available free of cost.

(iv) It is comparatively simple in construction and requires less

maintenance.

(v) It does not require a long starting time like a steam power station. In

fact, such plants can be

put into service instantly.

(vi) It is robust and has a longer life.

(vii) Such plants serve many purposes. In addition to the generation of

electrical energy, they

also help in irrigation and controlling floods.

(viii) Although such plants require the attention of highly skilled persons

at the time of construction, yet for operation, a few experienced persons

may do the job well.

Disadvantages:

(i) It involves high capital cost due to construction of dam.

(ii) There is uncertainty about the availability of huge amount of water

due to dependence on

weather conditions.

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(iii) Skilled and experienced hands are required to build the plant.

(iv) It requires high cost of transmission lines as the plant is located in

hilly areas which are quite

away from the consumers.

Schematic diagram of nuclear power plant:

Function of fuel rod, control rod and moderator:

Function of fuel rod: A long, slender, zirconium metal tube containing

pellets of fissionable material, which

provide fuel for nuclear reactors. Fuel rods are assembled into bundles

called fuel assemblies, which are loaded individually into

the reactor core.

Control rod: Control rods are used in nuclear reactors to control the

fission rate of uranium and plutonium. They are composed of chemical

elements such as boron, silver, indium and cadmium that are capable of

absorbing many neutrons without themselves fissioning.

Moderator: A nuclear power reactor controls the fission chain reaction

by moderating the neutrons and with the use of control rods which may

be inserted in the reactor core to absorb neutrons and slow down the

reaction.

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List of main and auxiliary equipment’s used in thermal power

station:

1. Coal handling plant

2. Pulverizing plant

3. Draft fans

4. Boiler

5. Ash handling plant

6. Turbine

7. Condenser

8. Cooling towers and ponds

9. Feed water heater

10. Economizer

11. Superheater and Reheater

12. Air preheater

Explanation:

(1) Coal handling plant: The function of coal handling plant is

automatic feeding of coal to the boiler furnace.

A thermal power plant burns enormous amounts of coal.

A 200MW plant may require around 2000 tons of coal daily

(2) Pulverizing plant: In modern thermal power plant , coal is

pulverised i.e. ground to dust like size and carried to the furnace in a

stream of hot air. Pulverising is a means of exposing a large surface

area to the action of oxygen and consequently helping combustion.

Pulverising mills are further classified as:

(i) Contact mill (ii) . Ball mill (iii) .Impact mill

(3) Draft fans: The circulation of air is caused by a difference in

pressure, known as Draft.

Draft is a differential pressure b/w atmosphere and inside the boiler.

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It is necessary to cause the flow of gases through boiler setting

It may be –

1. Natural draft 2. Mechanical draft

(4) Boiler: A boiler or steam generator is a closed vessel in which water

under pressure, is converted into steam.

It is one of the major components of a thermal power plant

Always designed to absorb maximum amount of heat released in the

process of combustion

Boilers are of two types-

1. Fire tube boiler 2. Water tube boiler

(5) Ash handling plant: The percentage of ash in coal varies from 5%

in good quality coal to about 40% in poor quality coal

Power plants generally use poor quality of coal , thus amount of ash

produced by it is pretty large

A modern 2000MW plant produces about 5000 tons of ash daily

The stations use some conveyor arrangement to carry ash to dump

sites directly or for carrying and loading it to trucks and wagons which

transport it to the site of disposal

(6) Turbine: A steam turbine converts heat energy of steam into

mechanical energy and drives the generator.

(7) Condenser: In thermal power plants, the purpose of a

surface condenser is to condense the exhaust steam from a steam

turbine to obtain maximum efficiency, and also to convert the turbine

exhaust steam into pure water (referred to as steam condensate) so

that it may be reused in the steam generator or boiler as boiler feed

water.

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(8) Cooling towers and ponds: A condenser needs huge quantity of

water to condense the steam.

Typically a 2000MW plant needs about 1500MGallon of water.

Most plants use a closed cooling system where warm water coming

from condenser is cooled and reused

Small plants use spray ponds and medium and large plants use cooling

towers.

Cooling tower is a steel or concrete hyperbolic structure having a

reservoir at the base for storage of cooled water

(9) Feed water heater: Feed water heating improves overall plant

efficiency.

The dissolved oxygen and carbon dioxide which would otherwise cause

boiler corrosion are removed in feed water heater

Thermal stresses due to cold water entering the boiler drum are

avoided.

Quantity of steam produced by the boiler is increased.

Some other impurities carried by the steam and condensate, due to

corrosion of boiler and condenser are precipitated outside the boiler.

(10) Economizer: Flue gases coming out of the boiler carry lot of heat.

An economiser extracts a part of this heat from flue gases and uses it

for heating feed water. This use of economiser results in saving coal

consumption and higher boiler efficiency

(11) Superheater: Superheater is a component of a steam-generating

unit in which steam, after it has left the boiler drum, is heated above its

saturation temperature. The amount of superheat added to the steam is

influenced by the location, arrangement, and amount of super heater

surface installed, as well as the rating of the boiler. The super heater

may consist of one or more stages of tube banks arranged to effectively

32

transfer heat from the products of combustion. Super heaters are

classified as convection , radiant or combination of these.

(12) Air preheater: After flue gases leave economiser, some further

heat can be extracted from them and used to heat incoming heat.

Cooling of flue gases by 20 degree centigrade increases the plant

efficiency by 1%.

Air preheaters may be of three types

Plate type

Tubular type

Regenerative type

Deaerator: A deaerator is a device that is widely used for the removal

of oxygen and other dissolved gases from the feedwater to steam-

generating boilers.

Techniques used to dissolved gases:

Mainly two types of techniques are used.

1. Reduce the pressure

2. Rise the temperature to saturation

Economizer save coal consumption and higher boiler efficiency in

thermal power plant:

As the name indicates the function of the economizer is to preheat the

boiler feed water before it is introduced into the drum by recovering heat

from the flue gases leaving the boiler.

Temperature inside economizer is about 3150C.

The heat of economizer and burnt coal combines thus it saves coal

consumption and increased higher boiler efficiency.

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advantages and disadvantages of thermal power plant:

advantages:

1. The design and layout of the plant are quite simple.

2. It occupies less space as the number and size of the auxiliaries is

small.

3. It can be located at any place.

4. It can be started quickly and can pick up load in a short time.

5. There are no standby losses.

6. It requires less quantity of water for cooling.

7. The overall cost is much less than that of steam power station of

the same capacity.

8. The thermal efficiency of the plant is higher than that of a steam

power station.

9. It requires less operating staff.

Disadvantages:

1. The plant has high running charges as the fuel (i.e., diesel) used is

costly.

2. The plant does not work satisfactorily under overload conditions for

a longer period.

3. The plant can only generate small power.

4. The cost of lubrication is generally high.

5. The maintenance charges are generally high.

6. Air pollution from smoke fumes

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Tide: Tides are the rise and fall of sea levels caused by the combined

effects of gravitational forces exerted by the Moon, Sun, and rotation of

the Earth.

Working of tidal power plant:

• two method used : Using turbines

• Using pushplates

USING TURBINES:

Production Of Power From Tidal Energy

Step 1: A location has to be found where there is sufficient tidal

changes to create enough energy to power turbines.

Step 2: A dam or barrage is created

Step 3: sluice gates allow the tides to fill the tidal basin

Step 4: water runs over the turbines which is connected to a

generator

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Wind Turbine: A wind turbine is device that converts the kinetic energy

from the wind into electrical power. Wind turbines, like aircraft propeller

blades, turn in the moving air and power an electric generator that

supplies an electric current.

Simply stated, a wind turbine is the opposite of a fan. Instead of using

electricity to make wind, like a fan, wind turbines use wind to make

electricity. The wind turns the blades, which spin a shaft, which

connects to a generator and makes electricity.

Working of wind turbine:

The energy in the wind turns the propeller-like blades around a rotor.

The pitch of the blades makes optimum use of the wind direction.

The rotor is connected to the main drive shaft, which spins a generator

to create electricity.

Wind turbines are mounted on a tower to capture the most energy. At

30 metres or more above ground, they can take advantage of faster and

less turbulent wind.

Wind turbines can be used to produce electricity for a single home or

building, or they can be connected to an electricity grid for more

widespread electricity distribution.

Solar energy uses in electrical applications:

• Toys, watches, calculators

• Remote lighting systems

• Water pumping

• Water treatment

• Emergency power

• Portable power supplies

• Satellites

36

• Solar cookers

• Vehicle running on solar power

• Charging phones

Inductive and dielectric heating:

Inductive heating: nduction heating is a method of heating conductive material by subjecting it to an alternating electromagnetic field, usually at frequencies between 100 and 500 kHz.

Oscillator circuits containing triodes are commonly used to generate the RF currents.

Typically induction heating is used in pipe welding and induction hardening/heat treatment.

Dielectric heating:

Dielectric heating (also known as Capacitance heating) is the method of

heating non-conductive materials. The material to be heated is placed

between two electrodes, to which a high-frequency energy source is

connected. The oscillating field passes through the material and as the

field direction changes, the polarization of individual molecules reverses

rapidly, causing friction and hence heat. The higher the frequency, the

greater the movement. Typically, frequencies in the range 5 MHz to 80

MHz are used. This technology is used in Wood Gluing, RF Drying and

Plastic Welding.

Electric furnaces: An electric arc is an electrical breakdown of a gas

resulting from a current flowing through normally nonconductive media

such as air.

An electric arc furnace (EAF) heats charged material by means of an

electric arc.

37

BRAKING SYSTEM in hydropower plant:

Electrical and Mechanical (auxiliary) braking is used for regular

braking. When hydro generator is disconnected from grid, turbine

wicket gate is closed and rotation speed is reduced down to 50%

of rated value, short-circuiting of main terminals of stator winding

and current supply into rotor winding from brake thyristor converter

occurs.

When rotation speed reduced down to 5% of rated value, the

mechanical breaking is automatically switched on .In case of

electrical braking system failure, or electrical damage of generator,

the mechanical breaking is automatically switched on, when

rotation speed will become 10% of rated value.