Seminar Report

A

SEMINAR REPORT ON

“ELECTRO STATIC PRECIPATOR”

Submitted in partial fulfillment of the requirement for the award of the degree

of

Bachelors of TechnologyIn

MECHANICAL

From

Rajasthan Technical University

Kota (Rajasthan)

Submitted to Submitted ByMr. Iqbal Mohammad CHITRANSH(Asst. Proff. of Mechanical.) Roll No. (09EMCME016)

DEPARTMENT OF MECHANICAL ENGINEERING

MODERN INSTITUTE OF TECHNOLOGY AND RESEARCH CENTRE

ALWAR(RAJ.)

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ACKNOWLEDGEMENT

I extend my sincere gratitude towards Mr. Mr. Iqbal Mohammad (Asst. Proff. of Mechanical.)for giving us this invincible knowledge and technical guidance.I express my thanks to all staff members of mechanical engineering department for their kind co-operation and guidance.I also thank all the other faculty members of ME department and my friends for their endless support.

Deevan Singh 09EMCME019

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ABSTRACT

Engineering is a theoretical study as well as practical study but it is an implantation of all

we study for creating something new and making things more easy and useful through

practical study.

The electricity produced in India by thermal power plants and hydroelectric power plants

are not sufficient as per the requirements and the loss of electricity and theft of electricity is

more in these processes. Thus, we have an idea of generating electricity by using wind

energy. The wind energy is readily available, abundant in quantity and also the cleanest

source of energy. It can be used for multiple purposes like generation of electricity,

compression of fluids and pumping of fluids.

In this project we will use a generator of appropriate volt, wind turbine, gear attachments.

The main objective of this project is to convert the mechanical forces into electricity with

the help of wind turbine.

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TABLE OF CONTENTS

CERTIFICATE IAKNOWLEDGEMENT IIABSTRACT IIIChapter Name1 INTRODUCTION

1.1 HISTORY

2 TRENDS IN GENERATION OF ELECTRICITY

2.1 THERMAL ENERGY

2.2 HYDRO ENERGY

2.3 NUCLEAR ENERGY

2.4 SOLAR ENERGY

2.5 WIND ENERGY

3 TECHNICAL DETAILS

3.1 WIND TURBINE

3.2 DESIGN BASICS

3.2.1 MATCHING THE ROTOR TO THE GENERATOR

3.3 BLADES

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3.3.1 TYPES OF BLADES

3.3.2 BLADE COUNT

3.3.3 BLADE DESIGN

3.3.4 BLADE MATERIALS

3.4 GENERATOR

3.4.1 GENERATOR CHARACTERSTICS

3.5 TOWER

3.5.1 TOWER HEIGHT

3.6 WIND RESOURCE

4 FUTURE SCOPE OF WIND ENERGY

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CHAPTER 1

INTRODUCTION

The report suggests about wind energy.In this seminar report we will learn that what is

wind energy in actual and what wind energy is used for. We know that electricity is the

most one need of everyone in this world. The growth of all the countries in this world is

based on the electricity and to fill up this need, there are many large electrical power plants

are established to generate the electricity. In india the electricity is generated in the thermal

power plants or hydroelectric power plants. India is a large country and the consumption of

power or electricity in India is very much. The power generation using thermal power

plants is very costly. To overcome this problem the wind energy comes to take action.

Wind Energy is the kind of energy that is produced by wind. Wind energy is mostly used in

the wind turbines and wind turbines can be used to generate the electricity. To produce the

electricity with wind energy we need only three things that are wind turbine, generator and

gear boxes. The wind turbine can be drived automatically with the help of wind energy and

the generator is used to convert this mechanical energy into the electrical energy. Wind

energy is a kinetic energy and this is converted into the mechanical energy by wind turbine

and this mechanical energy is converted into electrical energy by generator.A simple and

one wind turbine can produce the electricity sufficient for charging a battery but if someone

needs to generate a high amount of electricity, more wind turbines can be concated using

gear boxes. Wind is the most powerful force in the world and why should one not use this

natural resource (wind energy) to generate the electricity.

Wind energy can be used not only for producing the electrical power but also it can drive

the wind mills and wind pumps for irrigating the field.The force of the wind can be very

strong, as can be seen after the passage of a hurricane or a typhoon. Historically, people

have harnessed this force peacefully, its most important usage probably being the

propulsion of ships using sails before the invention of the steam engine and the internal

combustion engine. Wind has also been used in windmills to grind grain or to pump water

for irrigation or, as in The Netherlands, to prevent the ocean from flooding low-lying land.

At the beginning of the twentieth century electricity came into use and windmills gradually

became wind turbines as the rotor was connected to an electric generator

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1.1 HISTORY

Windmills were used in Persia (present-day Iran) as early as 200 B.C.The wind wheel of

Heron of Alexandria marks one of the first known instances of wind powering a machine in

history. However, the first known practical windmills were built in Sistan, a region

between Afghanistan and Iran, from the 7th century. These "Panemone" were vertical axle

windmills, which had long vertical driveshaft with rectangular blades. Made of six to

twelve sails covered in reed matting or cloth material, these windmills were used to grind

grain or draw up water, and were used in the gristmilling and sugarcane industries.

Windmills first appeared in Europe during the middle ages. The first historical records of

their use in England date to the 11th or 12th centuries and there are reports of German

crusaders taking their windmill-making skills to Syria around 1190. By the 14th century,

Dutch windmills were in use to drain areas of the Rhine delta.

The first electricity generating wind turbine, was a battery charging machine installed in

July 1887 by Scottish academic James Blyth to light his holiday home in Marykirk,

Scotland. Some months later American inventor Charles F Brush built the first

automatically operated wind turbine for electricity production in Cleveland, Ohio.

Although Blyth's turbine was considered uneconomical in the United Kingdom electricity

generation by wind turbines was more cost effective in countries with widely scattered

populations. In Denmark by 1900, there were about 2500 windmills for mechanical loads

such as pumps and mills, producing an estimated combined peak power of about 30 MW.

The largest machines were on 24-metre (79 ft) towers with four-bladed 23-metre (75 ft)

diameter rotors. By 1908 there were 72 wind-driven electric generators operating in the US

from 5 kW to 25 kW. Around the time of World War I, American windmill makers were

producing 100,000 farm windmills each year, mostly for water-pumping. By the 1930s,

wind generators for electricity were common on farms, mostly in the United States where

distribution systems had not yet been installed. In this period, high-tensile steel was cheap,

and the generators were placed atop prefabricated open steel lattice towers.

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A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in

1931. This was a 100 kW generator on a 30-metre (98 ft) tower, connected to the local 6.3

kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not

much different from current wind machines. In the fall of 1941, the first megawatt-class

wind turbine was synchronized to a utility grid in Vermont. The Smith-Putnam wind

turbine only ran for 1,100 hours before suffering a critical failure. The unit was not

repaired because of shortage of materials during the war.

Figure- The first automatically operated wind turbine.

Courtsey:Wikipedia(http://en.wikipedia.org/wiki/Wind_turbine)

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CHAPTER 2

TRENDS OF GENERATION OF ELECTRICITY

2.1 THERMAL ENERGY

A thermal power station is a power plant in which the prime mover is steam driven.

Water is heated, turns into steam and spins a steam turbine which drives an electrical

generator. After it passes through the turbine, the steam is condensed in a condenser and

recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in

the design of thermal power stations is due to the different fuel sources. Some prefer to use

the term energy center because such facilities convert forms of heat energy into electricity.[1] Some thermal power plants also deliver heat energy for industrial purposes, for district

heating, or for desalination of water as well as delivering electrical power. A large part of

human CO2 emissions comes from fossil fueled thermal power plants; efforts to reduce

these outputs are various and widespread.

2.2 HYDRO POWER

Hydropower, hydraulic power, hydrokinetic power or water power is power that is derived

from the force or energy of falling water, which may be harnessed for useful purposes.

Since ancient times, hydropower has been used for irrigation and the operation of various

mechanical devices, such as watermills, sawmills, textile mills, dock cranes, and domestic

lifts. Since the early 20th century, the term is used almost exclusively in conjunction with

the modern development of hydro-electric power, the energy of which could be transmitted

considerable distance between where it was created to where it was consumed.

Another previous method used to transmit energy had employed a trompe, which produces

compressed air from falling water that could then be piped to power other machinery at a

distance from the energy source.

Water's power is manifested in hydrology, by the forces of water on the riverbed and banks

of a river. When a river is in flood, it is at its most powerful, and moves the greatest

amount of sediment. This higher force results in the removal of sediment and other material

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from the riverbed and banks of the river, locally causing erosion, transport and, with lower

flow, sedimentation downstream

2.3 NUCLEAR POWER

Nuclear power is the use of sustained nuclear fission to generate heat and electricity.

Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's

electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear

generated electricity. In 2007 there were 439 nuclear power reactors in operation in the

world, operating in 31 countries. Also, more than 150 naval vessels using nuclear

propulsion have been built.

2.4 SOLAR POWER

Solar energy, radiant light and heat from the sun, has been harnessed by humans since

ancient times using a range of ever-evolving technologies. Solar energy technologies

include solar heating, solar photovoltaic, solar thermal electricity and solar architecture,

which can make considerable contributions to solving some of the most urgent problems

the world now faces.

Solar technologies are broadly characterized as either passive solar or active solar

depending on the way they capture, convert and distribute solar energy. Active solar

techniques include the use of photovoltaic panels and solar thermal collectors to harness

the energy. Passive solar techniques include orienting a building to the Sun, selecting

materials with favourable thermal mass or light dispersing properties, and designing spaces

that naturally circulate air.

In 2011, the International Energy Agency said that "the development of affordable,

inexhaustible and clean solar energy technologies will have huge longer-term benefits. It

will increase countries’ energy security through reliance on an indigenous, inexhaustible

and mostly import-independent resource, enhance sustainability, reduce pollution, lower

the costs of mitigating climate change, and keep fossil fuel prices lower than otherwise.

These advantages are global. Hence the additional costs of the incentives for early

deployment should be considered learning investments; they must be wisely spent and need

to be widely shared".

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2.5 WIND ENERGY

Wind is simply air in motion. It is caused by the uneven heating of the Earth’s surface by

radiant energy from the sun. Since the Earth’s surface is made of very different types of

land and water, it absorbs the sun’s energy at different rates. Water usually does not heat or

cool as quickly as land because of its physical properties. An ideal situation for the

formation of local wind is an area where land and water meet. During the day, the air above

the land heats up more quickly than the air above water. The warm air over the land

expands, becomes less dense and rises. The heavier, denser, cool air over the water flows in

to take its place, creating wind. In the same way, the atmospheric winds that circle the

Earth are created because the land near the equator is heated more by the sun than land near

the North and South Poles.

CHAPTER 3

TECHNICAL DETAILS

3.1 WIND TURBINE

Wind turbines are designed to exploit the wind energy that exists at a location.

Aerodynamic modelling is used to determine the optimum tower height, control systems,

number of blades and blade shape.

Wind turbines convert wind energy to electricity for distribution. Conventional horizontal

axis turbines can be divided into three components.

The rotor component, which is approximately 20% of the wind turbine cost, includes

the blades for converting wind energy to low speed rotational energy.

The generator component, which is approximately 34% of the wind turbine cost,

includes the electrical generator, the control electronics, and most likely a gearbox (e.g.

planetary gearbox adjustable-speed drive. or continuously variable transmission ] )

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component for converting the low speed incoming rotation to high speed rotation

suitable for generating electricity.

The structural support component, which is approximately 15% of the wind turbine

cost, includes the tower and rotor yaw mechanism.

A 1.5 MW wind turbine of a type frequently seen in the United States has a tower 80

meters high. The rotor assembly (blades and hub) weighs 48,000 pounds (22,000 kg). The

nacelle, which contains the generator component, weighs 115,000 pounds (52,000 kg). The

concrete base for the tower is constructed using 58,000 pounds (26,000 kg) of reinforcing

steel and contains 250 cubic yards (190 cubic meters) of concrete. The base is 50 feet

(15 m) in diameter and 8 feet (2.4 m) thick near the centre.

Like old-fashioned windmills, today’s wind turbines use blades to capture the wind’s

kinetic energy. Wind turbines work because they slow down the speed of the wind. When

the wind blows, it pushes against the blades of the wind turbine, making them spin. They

power a generator to produce electricity. Most wind turbines have the same basic parts:

blades, shafts, gears, a generator, and a cable. (Some turbines do not have gearboxes.)

These parts work together to convert the wind’s energy into electricity.

1. The wind blows and pushes against the blades on top of the tower, making them spin.

2. The turbine blades are connected to a low-speed drive shaft. When the blades spin, the

shaft turns. The shaft is connected to a gearbox. The gears in the gearbox increase the

speed of the spinning motion on a high-speed drive shaft.

3. The high-speed drive shaft is connected to a generator. As the shaft turns inside the

generator, it produces electricity.

4. The electricity is sent through a cable down the turbine tower to a transmission line.

The amount of electricity that a turbine produces depends on its size and the speed of the

wind. Wind turbines come in many different sizes. A small turbine may power one home.

Large wind turbines can produce enough electricity to power up to 1,000 homes.

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ADVANTAGES OF WIND TURBINE

Cost

Wind is free. This means unlike other fuel sources, there is no cost for materials used to

create power. Wind is also a continuing resource, and will not run out from overuse.

Environment

Once a wind turbine is built, the energy created does not emit greenhouse gasses, so the

effect on the ozone is basically nothing. There are no pollutants, like with coal or fossil

fuels.

Size

Wind turbines are very tall, but they take up a relatively small plot of land. This means the

surrounding land can still be used for things, like farming. Wind turbines can also be

placed pretty much anywhere.

Range of Use

Wind turbines come in a variety of sizes. This makes them accessible in ways other power

conversion methods are not. Homes, corporations or giant wind farms, can all convert wind

for power usage.

Expansion of Power

Remote areas that are not easily connected into main power grids, can establish wind

turbines, and thus create their own power. This allows them to sustain themselves much

easier, and also means that Third World nations can expand and tap into energy in a new

way.

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3.2 DESIGN BASICS

3.2.1 MATCHING THE ROTOR TO THE GENERATOR

For a given size of rotor, it is tempting to use a very large generator, to make use of the

high power in high winds. But, for a given size of generator it is tempting to use a very

large rotor, so as to obtain full power in low winds. A big generator with a small rotor will

very seldom be operating at rated power, so it will be disappointing, especially if the

generator's part-load efficiency is poor. A small generator with a large rotor will achieve

full power in low winds, giving a more constant power supply. The drawbacks are that the

larger rotor will:

• need a stronger tower

• run at lower rpm

• require more control in high winds

The usual compromise is to choose a generator which reaches full output in a wind speed

around ten metres per second (10 m/s).It is also vital to match the rotational speed (rpm) of

these two components, for which we need to understand their power/ speed characteristics.

3.2.2 TIP SPEED RATIO

The speed of the tip of one blade depends on the revolutions per minute (or rpm), and the

rotor diameter. For example, the tip of a two metre diameter rotor, running at 500 rpm,

travels at about 52 metres per second. This is over 100 mph! Operating tip speeds of up to

134 m/s (300 mph) are not unknown, but for the sake of a quiet life you should try to keep

it below 80 m/s. Tip speed ratio is the magic number which most concisely describes the

rotor of a windmill. It is how many times faster than the wind speed the blade tip is

designed to run. A windmill rotor does not simply have a best rotational speed (e.g. 600

rpm). Its optimum rpm will depend on the wind speed, the diameter and the tip speed ratio.

The windmill rotor will do best at a particular tip speed ratio, but it will inevitably have to

work over a range of speeds. The power coefficient 'ep' will vary depending on tip speed

ratio, for any particular rotor design. It will be best at the 'design' or 'rated' tip speed ratio,

but acceptable over a range of speeds designed to operate at a tip speed ratio of 7. A small

shift in rpm or wind speed will not make much difference. If the rpm is too low, compared

to the wind, then it will stall, and performance will drop. If there is no load on the rotor

(perhaps because a wire has broken in the electrical circuit), the rotor will over speed until

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it reaches a certain point, where it becomes so inefficient that it has no power to go faster.

Most windmills are quite noisy and alarming at runaway tip speed.

3.3 BLADES

3.3.1 TYPES OF BLADES

Wind turbines are one of the oldest devices in existence used for generating power. With

time, design aspects of wind generators have steadily improved, especially when it comes

to how the blades that are responsible for turning the turbines’ rotors have been built.

Today, wind turbines generate much more power from much less wind than ever before,

which is largely thanks to these improvements .The earliest wind turbine blades were

basically just large mats made from reeds . While they did the job under some conditions,

they weren’t very durable. The short lifespan of this type of blade led inventors to seek out

other options.

Cloth sails were the next step in the development of wind turbine blades. Thanks to this

blade design, early windmills were able to harness wind power effectively in order to

process grain.

The next major kind of blade to be introduced was the wood blade, which was often used

in conjunction with a horizontal axis configuration. This development mimicked those seen

in the world of aeronautics, as improving rotors often had these characteristics. Although

much lighter, wooden blades were nevertheless able to provide much more power than

earlier turbine blades.

Electricity was generated for the first time from wind turbines thanks to these designs. The

earliest wind turbines of this type were relatively small in size, but they would soon be

enlarged and used for commercial purposes.

In order to meet divergent requirements, the differences between horizontal axis turbine

blade designs and vertical axis blade designs started to become even more distinct. With

regard to horizontal axis blade design, most of the changes would manifest themselves as

differences in blade shape and pitch, materials, and the number of blades used per rotor.

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Due to their strong balance of stability and rotor speed, 3-blade designs came to be the

standard for horizontal axis wind turbines. In many current turbines, composite blades are

used, which are extremely strong and flexible in addition to being lightweight, making

them excellent for both residential and commercial uses. Unlike previous generations of

turbines, these new turbines can both spin at higher speeds and pick up winds of lower

velocity.

For vertical axis wind turbines too, there are a number of new designs available currently,

appropriate for a wide variety of purposes. The rotation for these units is usually provided

by features that take advantage of either the lift or drag of the wind.

The big advantage of vertical axis wind turbine designs is their capacity to generate power

regardless of wind direction. In this regard, they provide a more consistent supply of power

than standard horizontal axis turbines. What’s more, because vertical axis turbines usually

don’t require a tower, they’re often favored by residential users.

There are several excellent formulas out there which are a bit more scientific, but the goal

here is to keep things simple and inexpensive. We don’t believe we need to use a terribly

thick board, or have really steep angles at the root like most correct formulas would tell us.

Here we make blades from standard 2" thick lumber. The very steep pitch that most blade

formulas would call for at the root requires much thicker lumber. Such blades are a bit

more work - the wood is more expensive and they may start-up easier in low winds,

although we don't believe that's an issue, especially with very free spinning dual rotor

alternators. Machines we make with blades start turning in very low winds (below 5mph)

and come up to speed quickly - they seem very responsive. They also seem reasonably

efficient across the range of wind speeds. 10' diameter machines we use these blades on

frequently produce over 1000 watts in winds below 30 mph and they seem quite reasonable

in lower winds.

There are lots of ways of doing things. We prefer to make blades from wood for the

following reasons. It's easy to work with, a person can make a nice blade from wood with

simple tools fairly quickly. It's fairly inexpensive. It has an excellent strength/weight ratio,

and it stands up to fatigue very well. If its finished reasonably well and maintained it can

last practically forever. I've seen 70 year old Win chargers running with their original

Cedar blades. Lots of different types of wood can be used. It seems like lighter weight

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'pines' are the best bet - white pine, fir, Spruce ... we've used lodgepole. Lately Cedar has

been our favourite, its very light, very easy to work... it doesn't rot. We've made blade sets

from single boards - lately we prefer to laminate up smaller boards, it makes things a bit

stronger and we can use less expensive lumber.

Simple tools are required to work with wood. The whole job could be done with a

drawknife, a hand saw, and a plane. A hammer, chisel can be handy sometimes too. A few

power tools can speed things up a lot.

3.3.2 BLADE DESIGN

The ratio between the speed of the blade tips and the speed of the wind is called tip speed

ratio. High efficiency 3-blade-turbines have tip speed/wind speed ratios of 6 to 7. Modern

wind turbines are designed to spin at varying speeds. Use of aluminium and composite

materials in their blades has contributed to low rotational inertia, which means that newer

wind turbines can accelerate quickly if the winds pick up, keeping the tip speed ratio more

nearly constant. Operating closer to their optimal tip speed ratio during energetic gusts of

wind allows wind turbines to improve energy capture from sudden gusts that are typical in

urban settings.

In contrast, older style wind turbines were designed with heavier steel blades, which have

higher inertia, and rotated at speeds governed by the AC frequency of the power lines. The

high inertia buffered the changes in rotation speed and thus made power output more

stable.

The speed and torque at which a wind turbine rotates must be controlled for several

reasons:

To optimize the aerodynamic efficiency of the rotor in light winds.

To keep the generator within its speed and torque limits.

To keep the rotor and hub within their centrifugal force limits. The centrifugal force

from the spinning rotors increases as the square of the rotation speed, which makes this

structure sensitive to over speed.

To keep the rotor and tower within their strength limits. Because the power of the wind

increases as the cube of the wind speed, turbines have to be built to survive much

higher wind loads (such as gusts of wind) than those from which they can practically

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generate power. Since the blades generate more torsional and vertical forces (putting

far greater stress on the tower and nacelle due to the tendency of the rotor to precess

and nutate) when they are producing torque, most wind turbines have ways of reducing

torque in high winds.

To enable maintenance. Since it is dangerous to have people working on a wind turbine

while it is active, it is sometimes necessary to bring a turbine to a full stop.

To reduce noise. As a rule of thumb, the noise from a wind turbine increases with the

fifth power of the relative wind speed (as seen from the moving tip of the blades). In

noise-sensitive environments, the tip speed can be limited to approximately 60 m/s

(200 ft/s).

It is generally understood that noise increases with higher blade tip speeds. To increase tip

speed without increasing noise would allow reduction the torque into the gearbox and

generator and reduce overall structural loads, thereby reducing cost. The reduction of noise

is linked to the detailed aerodynamics of the blades, especially factors that reduce abrupt

stalling. The inability to predict stall restricts the development of aggressive aerodynamic

concepts.

3.3.3 BLADE COUNT

The determination of the number of blades involves design considerations of aerodynamic

efficiency, component costs, system reliability, and aesthetics. Noise emissions are affected

by the location of the blades upwind or downwind of the tower and the speed of the rotor.

Given that the noise emissions from the blades' trailing edges and tips vary by the 5th

power of blade speed, a small increase in tip speed can make a large difference.

Wind turbines developed over the last 50 years have almost universally used either two or

three blades. Aerodynamic efficiency increases with number of blades but with

diminishing return. Increasing the number of blades from one to two yields a six percent

increase in aerodynamic efficiency, whereas increasing the blade count from two to three

yields only an additional three percent in efficiency. Further increasing the blade count

yields minimal improvements in aerodynamic efficiency and sacrifices too much in blade

stiffness as the blades become thinner.

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Component costs that are affected by blade count are primarily for materials and

manufacturing of the turbine rotor and drive train. Generally, the fewer the number of

blades, the lower the material and manufacturing costs will be. In addition, the fewer the

number of blades, the higher the rotational speed can be. This is because blade stiffness

requirements to avoid interference with the tower limit how thin the blades can be

manufactured, but only for upwind machines; deflection of blades in a downwind machine

results in increased tower clearance. Fewer blades with higher rotational speeds reduce

peak torques in the drive train, resulting in lower gearbox and generator costs.

System reliability is affected by blade count primarily through the dynamic loading of the

rotor into the drive train and tower systems. While aligning the wind turbine to changes in

wind direction (yawing), each blade experiences a cyclic load at its root end depending on

blade position. This is true of one, two, three blades or more. However, these cyclic loads

when combined together at the drive train shaft are symmetrically balanced for three

blades, yielding smoother operation during turbine yaw. Turbines with one or two blades

can use a pivoting teetered hub to also nearly eliminate the cyclic loads into the drive shaft

and system during yawing.

Finally, aesthetics can be considered a factor in that some people find that the three-bladed

rotor is more pleasing to look at than a one- or two-bladed rotor.

3.3.4 BLADE MATERIALS

Wood and canvas sails were used on early windmills due to their low price, availability,

and ease of manufacture. Smaller blades can be made from light metals such as aluminium.

These materials, however, require frequent maintenance. Wood and canvas construction

limits the airfoil shape to a flat plate, which has a relatively high ratio of drag to force

captured (low aerodynamic efficiency) compared to solid airfoils. Construction of solid

airfoil designs requires inflexible materials such as metals or composites.

New wind turbine designs push power generation from the single megawatt range to

upwards of 10 megawatts using larger and larger blades. A larger area effectively increases

the tip-speed ratio of a turbine at a given wind speed, thus increasing its energy extraction.

Computer-aided engineering software such as HyperSizer can be used to improve blade

design.

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Current production wind turbine blades are as large as 100 meters in diameter with

prototypes in the range of 110 to 120 meters. In 2001, an estimated 50 million kilograms of

fibreglass laminate were used in wind turbine blades.

An important goal of larger blade systems is to control blade weight. Since blade mass

scales as the cube of the turbine radius, loading due to gravity constrains systems with

larger blades.

Manufacturing blades in the 40 to 50 meter range involves proven fibreglass composite

fabrication techniques. Manufactures such as Nordex and GE Wind use an infusion

process. Other manufacturers use variations on this technique, some including carbon and

wood with fibreglass in an epoxy matrix. Options also include prepreg fiberglass and

vacuum-assisted resin transfer molding. Each of these options use a glass-fibre reinforced

polymer composite constructed with differing complexity. Perhaps the largest issue with

more simplistic, open-mold, wet systems are the emissions associated with the volatile

organics released. Preimpregnated materials and resin infusion techniques avoid the release

of volatiles by containing all reaction gases. However, these contained processes have their

own challenges, namely the production of thick laminates necessary for structural

components becomes more difficult. As the preform resin permeability dictates the

maximum laminate thickness, bleeding is required to eliminate voids and insure proper

resin distribution. One solution to resin distribution a partially preimpregnated fiberglass.

During evacuation, the dry fabric provides a path for airflow and, once heat and pressure

are applied, resin may flow into the dry region resulting in a thoroughly impregnated

laminate structure.

Epoxy-based composites have environmental, production, and cost advantages over other

resin systems. Epoxies also allow shorter cure cycles, increased durability, and improved

surface finish. Prepreg operations further reduce processing time over wet lay-up systems.

As turbine blades pass 60 meters, infusion techniques become more prevalent; the

traditional resin transfer moulding injection time is too long as compared to the resin set-up

time, limiting laminate thickness. Injection forces resin through a thicker ply stack, thus

depositing the resin where in the laminate structure before gelatine occurs. Specialized

epoxy resins have been developed to customize lifetimes and viscosity.

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Carbon fibre-reinforced load-bearing spars can reduce weight and increase stiffness. Using

carbon fibres in 60 meter turbine blades is estimated to reduce total blade mass by 38% and

decrease cost by 14% compared to 100% fibreglass. Carbon fibres have the added benefit

of reducing the thickness of fibreglass laminate sections, further addressing the problems

associated with resin wetting of thick lay-up sections. Wind turbines may also benefit from

the general trend of increasing use and decreasing cost of carbon fibre materials.

3.4 GENERATOR

In electricity generation, an electric generator is a device that converts mechanical energy

to electrical energy. A generator forces electric charge (usually carried by electrons) to

flow through an external electrical circuit. It is analogous to a water pump, which causes

water to flow (but does not create water). The source of mechanical energy may be a

reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an

internal combustion engine, a wind turbine, a hand crank, compressed air or any other

source of mechanical energy.

The reverse conversion of electrical energy into mechanical energy is done by an electric

motor, and motors and generators have many similarities. In fact many motors can be

mechanically driven to generate electricity, and very frequently make acceptable

generators.

For large, commercial size horizontal-axis wind turbines, the generator is mounted in a

nacelle at the top of a tower, behind the hub of the turbine rotor. Typically wind turbines

generate electricity through asynchronous machines that are directly connected with the

electricity grid. Usually the rotational speed of the wind turbine is slower than the

equivalent rotation speed of the electrical network - typical rotation speeds for a wind

generators are 5-20 rpm while a directly connected machine will have an electrical speed

between 750-3600 rpm. Therefore, a gearbox is inserted between the rotor hub and the

generator. This also reduces the generator cost and weight.

Older style wind generators rotate at a constant speed, to match power line frequency,

which allowed the use of less costly induction generators. Newer wind turbines often turn

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at whatever speed generates electricity most efficiently. This can be solved using multiple

technologies such as doubly fed induction generators or full-effect converters where the

variable frequency current produced is converted to DC and then back to AC, matching the

line frequency and voltage. Although such alternatives require costly equipment and cause

power loss, the turbine can capture a significantly larger fraction of the wind energy. In

some cases, especially when turbines are sited offshore, the DC energy will be transmitted

from the turbine to a central (onshore) inverter for connection to the grid.

3.4.1 GENERATOR CHARACTERISTICS

The rotor will accelerate until the load (generator) absorbs all the power it can produce. If

the generator and the rotor are well matched, this will occur at the design tip speed ratio,

and the maximum power will be extracted from the wind. Generators also have their

preferred speeds of operation. As we shall see later, the voltage produced by a generator

varies with the speed of rotation. It will need to be run fast. If it is connected to a battery,

then no power will come out of the generator until its output voltage exceeds the battery

voltage.

The shaft speed (rpm) above which the generator delivers power is known as the cut-in

speed. The speed required for full power output is known as the rated speed. These speeds

need to correspond to the speeds at which the rotor 'likes' to run, in the corresponding wind

speeds.

3.5 TOWER

3.5.1 TOWER HEIGHT

Wind velocities increase at higher altitudes due to surface aerodynamic drag (by land or

water surfaces) and the viscosity of the air. The variation in velocity with altitude, called

wind shear, is most dramatic near the surface.

Typically, in daytime the variation follows the wind profile power law, which predicts that

wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a

turbine, then, increases the expected wind speeds by 10% and the expected power by 34%.

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To avoid buckling, doubling the tower height generally requires doubling the diameter of

the tower as well, increasing the amount of material by a factor of at least four.

At night time, or when the atmosphere becomes stable, wind speed close to the ground

usually subsides whereas at turbine hub altitude it does not decrease that much or may even

increase. As a result the wind speed is higher and a turbine will produce more power than

expected from the 1/7 power law: doubling the altitude may increase wind speed by 20% to

60%. A stable atmosphere is caused by radiative cooling of the surface and is common in a

temperate climate: it usually occurs when there is a (partly) clear sky at night. When the

(high altitude) wind is strong (a 10-meter ) wind speed higher than approximately 6 to

7 m/s the stable atmosphere is disrupted because of friction turbulence and the atmosphere

will turn neutral. A daytime atmosphere is either neutral (no net radiation; usually with

strong winds and/or heavy clouding) or unstable (rising air because of ground heating—by

the sun). Here again the 1/7 power law applies or is at least a good approximation of the

wind profile. Indiana had been rated as having a wind capacity of 30,000 MW, but by

raising the expected turbine height from 50 m to 70 m, the wind capacity estimate was

raised to 40,000 MW, and could be double that at 100 m

3.6 WIND RESOURCE

A wind turbine transforms the kinetic energy in the wind to mechanical energy in a shaft

and finally into electrical energy in a generator. The maximum available energy, Pmax, is

thus obtained if theoretically the wind speed could be reduced to zero: P = 1/2M* VO 2 =

1/2 ρA VO 3 where m is the mass flow, VO is the wind speed, the density of the air and A the

area where the wind speed has been reduced. The equation for the maximum available

power is very important since it tells us that power increases with the cube of the wind

speed and only linearly with density and area. The available wind speed at a given site is

therefore often first measured over a period of time before a project is initiated. In practice

one cannot reduce the wind speed to zero, so a power coefficient Cp is defined as the ratio

between the actual power obtained and the maximum available power as given by the

above equation. A theoretical maximum for Cp exists, denoted by the Betz limit, CPmax =

16/27 = 0.593. Modern wind turbines operate close to this limit, with Cp up to 0.5, and are

therefore optimized. Statistics have been given on many different turbines sited in

Denmark and as rule of thumb they produce approximately 1000kWh/m2/year. However,

the production is very site dependent and the rule of thumb can only be used as a crude

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estimation and only for a site in Denmark. Sailors discovered very early on that it is more

efficient to use the lift force than simple drag as the main source of propulsion. Lift and

drag are the components of the force perpendicular and parallel to the direction of the

relative wind respectively. It is easy to show theoretically that it is much more efficient to

use lift rather than drag when extracting power from the wind. All modern wind turbines

therefore consist of a number of rotating blades looking like propeller blades. If the blades

are connected to a vertical shaft, the turbine is called a vertical-axis machine, VAWT, and

if the shaft is horizontal, the turbine is called a horizontal-axis wind turbine, HAWT.

The tower height is important since wind speed increases with height above the ground and

the rotor diameter is important since this gives the area A in the formula for the available

power. The ratio between the rotor diameter D and the hub height H is often approximately

one. The rated power is the maximum power allowed for the installed generator and the

control system must ensure that this power is not exceeded in high winds. The number of

blades is usually two or three. Two-bladed wind turbines are cheaper since they have one

blade fewer, but they rotate faster and appear more flickering to the eyes, whereas three-

bladed wind turbines seem calmer and therefore less disturbing in a landscape. The

aerodynamic efficiency is lower on a two bladed than on a three-bladed wind turbine. A

two-bladed wind turbine is often, but not always, a downwind machine; in other words the

rotor is downwind of the tower. Furthermore, the connection to the shaft is flexible, the

rotor being mounted on the shaft through a hinge. This is called a teeter mechanism and the

effect is that no bending moments are transferred from the rotor to the mechanical shaft.

Such a construction is more flexible than the stiff three-bladed rotor and some components

can be built lighter and smaller, which thus reduces the price of the wind turbine. The

stability of the more flexible rotor must, however, be ensured. Downwind turbines are

noisier than upstream turbines, since the once-per-revolution tower passage of each blade is

heard as a low frequency noise. The rotational speed of a wind turbine rotor is

approximately 20 to 50 rpm and the rotational speed of most generator shafts is

approximately 1000 to 3000 rpm. Therefore a gearbox must be placed between the low-

speed rotor shaft and the speed generator shaft.

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CHAPTER 4

FUTURE SCOPE OF WIND ENERGY

In the near future, wind energy will be the most cost effective source of electrical power. In

fact, a good case can be made for saying that it already has achieved this status. The actual

life cycle cost of fossil fuels (from mining and extraction to transport to use technology to

environmental impact to political costs and impacts, etc.) is not really known, but it is

certainly far more than the current wholesale rates. The eventual depletion of these energy

sources will entail rapid escalations in price which -- averaged over the brief period of their

use -- will result in postponed actual costs that would be unacceptable by present standards.

And this doesn't even consider the environmental and political costs of fossil fuels use that

are silently and not-so-silently mounting every day.

The major technology developments enabling wind power commercialization have already

been made. There will be infinite refinements and improvements, of course. One can guess

(based on experience with other technologies) that the eventual push to full

commercialization and deployment of the technology will happen in a manner that no one

can imagine today. There will be a "weather change" in the marketplace, or a "killer

application" somewhere that will put several key companies or financial organizations in a

position to profit. They will take advantage of public interest, the political and economic

climate, and emotional or marketing factors to position wind energy technology for its next

round of development.

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