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A STUDY OF WIND POWERED TURBINE GENERATION

BY

EZUGWU, NICHOLAS U.

REG. NO: PGD/EEE/2003235010

DEPARTMENT OF ELECTRICAL/ELECTRONICS ENGINEERING SCHOOL OF POSTGRADUATE STUDIES

FACULTY OF ENGINEERING AND TECHNOLOGY

NNAMDI AZIKIWE UNIVERSITY, AKWA

2007

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APPROVAL PAGE

This project report entitled “A Study of Wind Powered Turbine Generation”

by Ezugwu Nicholas U. meet the regulations governing the award of the

Degree of Post Graduate Diploma (PGD) in Electrical /Electronic Engineering

of Nnamdi Azikwe University, Akwa and is approval or its contribution to

knowledge and literacy presentation.

-------------------------- --------------------------

Engr O. A Ezechukwu Engr F.O. Enemoh

Supervisor Head of Department

------------------------------

External Examiner

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DEDICATION

I am dedicating this project to my parents Mr. & Mrs. Steve U. Ezugwu, my

lovely wife Mrs. Ezugwu Nnenna and my only beloved sister Ezugwu, R.N.

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ACKOWLEDGEMENT

I wish to use this medium to thank the Almighty God for taking me this far. For

it is only by his mercy that am able to make this programme to the end. It is

now time to give him thanks and praise for he has lifted me up at last.

I cannot forget the encouraging, fatherly and inspirational words of my

project supervisor Engr. O.A. Ezechukwu who inspite of his tight schedules,

still made out time to meet me and discuss issue that led to the successful end of

this project.

My regards to my brothers Dr. Ezugwu C.O. and Ezugwu F.A. who due

to their financially commitment saw me through. May the good Lord guide and

protect them for me. May God grant them and their beloved families all their

heart desires that are not evil.

May the peace and love of God be with every soul that contributed in any

way to the success of this project all the days of their lives Amen.

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ABSTRACT

The (PHCH) Power Holding Company of Nigeria Plc, effort to provide us with

a regular power supply has not yet been achieved. And it is because of the

search for another means of power generation that necessitated the development

of wind turbine.

The wind energy is abundant in several parts. Among the numerous

natural energy resources that Nigeria was blessed with, wind is among the once

in great quantity. Wind can be used in conjunction with turbines to produce

electricity in isolation to supply numerous consumers. The PHCN can as well

use it to serve its customer be it commercial or residential load. It is because of

this aggressive search that in this paper I try to discuss various methods of

converting wind energy to electrical energy. The places it is obtainable and how

it can be best used to achieve maximum result in Nigeria.

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TABLE OF CONTENTS

Title page i

Approval page ii

Dedication iii

Acknowledgement iv

Abstract v

Table of contents vi

CHAPTER ONE

1.0 Introduction 1

1.1 Background of study 2

1.2 Energy from wind 4

CHAPTER TWO

2.0 Consideration for wind powered generator 6

2.1 Basic principal of wind power generation 9

2.2 Performance 12

CHAPTER THREE LITERATURE REVIEW

3.0 Types of wind machine 13

3.1 Horizontal axis wind turbine 13

3.2 Vertical axis wind turbine 15

3.3 Power in the wind 17

3.4 Matching wind turbine to load 19

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CHAPTER FOUR DESIGN SPECIFICATION FOR WIND TURBINE

4.0 Strength Calculation for Structural Analysis & Safety 21

4.1 System Design 25

4.2 Integration and Control 30

CHAPTER FIVE

5.0 Viability in Nigeria 32

5.1 Analysis of Wind Resource 34

5.2 Identification of Wind Data Source 36

5.3 Advantages 39

CHAPTER SIX

6.0 Conclusion 41

Reference 43

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CHAPTER ONE

1.0 INTRODUCTION

Since ancient times, people have harnessed the winds and energy. Over 5,000 years

ago, the ancient Egyptians used wind to sail ships on the Nile River. Later, people built

wind mills to grind wheat and other grains. The earliest known wind mills were in

Persia. These early wind mills looked like large paddle wheels. Centuries later, the

basic design of the wind mills was improved. It was given a propeller type blade. The

evolution has been slow but continuous, with two major phases. The first in which

wind energy was directly use for mechanical work, as in windmills, sawmills, water

lifting etc. and a second phase in which mechanical energy was changed into electrical

energy.

Since their first appearance, it have undergone many changes and improvements

in their major components. For instance, the major structure varied from wood frames

to more stable masonry works and subsequently to steel frames.

The interest here is on manufacturing system of which my goal will be looking at wind

as a means to effective power generation and system integration given a complete

program activities addressing electric power market rules.

This wind in question has played a long and important role in the history of human

civilization and is the world fastest growing energy technology, when

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flowing wind is captured and is turned into electricity and this process is called

HYBRID WIND SYSTEM OR WIND GENERATED POWER.

Wind powered generation. Turbine and generator coverts the energy into

electricity which can be used in isolation or fed into the electrical grid to be used in

homes, farms, business and by industries.

1.1 BACKGROUND OF STUDY

As the search for energy is now probing the realm of the wind and the sun,

human beings are sure to get a lasting solution to electricity problem. In using energy

to produce mechanical work, humans, since the beginning of civilization, have focused

their attention on those forces found explicit in

nature. Animal, hydraulic, and wind energy did not require transformation into other

energy types.

Instead, the use of such energy type necessitated the invention of mechanisms

whose complexity has constantly increased with the progress of technology. In

particular, since ancient times, the kinetic energy of the wind has been used to propel

ships and machines, such as windmill that proceeded the industrial age. The wind

power has been used for the production of electricity itself, but in small scale.

However, because of world wide energy crisis, wind energy once again is being

studied for large-scale application, along with other

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sources neglected. In the utilization of the wind or other natural energy forms, the

unlimited potentials of the source must be recognized in contraposition to the limited

supply of fossil fuel presently used.

Solar energy, which generates the wind is considered unlimited. The relationship

between the dynamic force in the wind and solar radiation is direct. Another major

characteristic of wind energy is the absence of any form of pollution, either in its direct

utilization for the production of mechanical work or in its transformation into electrical

energy. Yet, despite such positive factors, wind energy was neglected until a few years

ago. An estimate 1% to

3% of energy from the sun that hit the earth is converted into wind energy.

Most of this energy can be found at high altitude where continuous wind speeds over

160km/h (100mph) occur. This wind energy is converted through friction into diffuse

heat throughout the earth’s surface and the atmosphere.

The wind power estimated apply to areas free to local obstruction to wind terrain

features that are well exposed to wind such as open plains, table/and hilltops, Exposed

coastal areas are also rice potentials for wind application.

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1.2 ENERGY FROM-WIND

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

the sun. Since the earth’s surface is made of very different types of land and water, it

absorbs the sun’s heat at different rates. During the day, the air above the land heats up

more quickly than the air over water. The warm air over the land expands and rises,

and the heavier, cooler air rushes in to take its place. Creating winds at night, the winds

are reversed because the air cools more rapidly over land than over water.

In the same way, the large atmospheric winds that circle the earth are created because

the land near the earth’s equators is heated more by the sun than the land near the north

and South Pole.

Today, wind energy is mainly used to generate electricity. Wind is called a

renewable energy sources because the wind will blow as long as the sun shines.

Valleys often experience calm conditions at night even when adjacent hilltops are

windy, cool, heavy air drains from hillside and collects in the valleys. The resulting

layer of air is removed from the general flow above it to produce the calm condition in

the low lands.

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Fig 1

Because of this, a wind turbine located on a hill may be able to produce power all

night, while one located at a lower operation stands idle. This phenomenon is more

likely to occur on high terrain features that reach at least several hundreds feet above

the surrounding land. High terrain features can accelerate the flow of wind. An

approaching air mass is often squeezed into a thinner layer so it speeds up as it crosses

the summit. Over a ridge, maximum acceleration occurs when the wind blows

perpendicular to the ridge side. Isolated hills and mountains may accelerate the wind

less than ridges because more of the air tends to flow around the side. The downward

side of high terrain features should be avoided because of the presence of high wind

turbulence.

Land areas adjacent to large bodies of water may be good wind site for two

reasons. First, a water surface is smoother than land surface so air flowing over water

encounters little frictions. The best shoreline site is one where the wind direction is “on

shore”. Second when regional wind are light as on a sunny day local wind known as

sea or lake breeze can develop because the land and water surface heat up at different

rate.

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CHAPTER TWO

2.0 CONSIDERATION FOR WIND POWERED GENERATOR

In the 1970s, oil shortage pushed the development of alternative energy source. In

1990s, the push came from a renewed concern for the environment in response to

scientific studies indicating potential changes to the global climate if the use of fossils

fuels continuous to increase. Wind is a clean fuel; wind farms produce no air or water

pollution because no fuel is burnt.

Providing new cost effective advanced and innovative technologies valuation and

performance metrics that will enhance environmental performance and greater

efficiencies. The basic design concept for a wind powered outfit can be seen as in fig.

2.1 inside the wind turbine.

Inside the wind turbine

Fig.2.1

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This section defines the various part and instrument found inside the wind turbine.

Anemometer: This is an instrument which is used to measure the wind speed by

rotating in the wind and generates a signal proportional to the wind speed and transmit

wind speed data to the controller. Most of which are designed with cups mounted on

shaft arms connected to a rotating vertical shaft.

Controller: The controller starts up the machine at wind speed at about 8 to 16 miles

per hour (mph) and shuts off the machine at about 65mph. Turbines.

Cannot operate at wind speed above the rate of 65mph because their generators could

overheat.

Generators: This is usually an off the shell induction generator that produces 60 cycle

A.C electricity.

Gear Box: Gear box connect low-speed shaft to the high-speed shaft from about 30 to

60 rotations per minute (rpm) to 1200 to 1500 rpm, the rotational speed required by

most generators to produce electricity. This gear box is a costly and heavy part of the

wind turbine.

Low-Speed Shaft: This is the connecting pipe between the rotor and the gear box.

Rotor: This is made up of the blade and the hub. It is a portion of the wind turbine that

collects energy from the wind and rotates about an axis (horizontally or vertically) at a

rate determined by the wind speed and shape of

the blade. The blade is attached to the hub, which in turn is attached to the main shaft.

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Brake: A disc brake which can be applied mechanically, electrically or hydraulically

to stop the rotor in emergencies is used.

Yaw Drive: This is an equipment that is used to keep the rotor facing into the wind as

the wind direction changes. It is only found in the upwind turbine.

Yaw Motor: This powers the yaw driver.

High Speed Shaft: This drives the generator.

Wind Vane: This is an instrument that measures or decodes the wind direction and

communicate with the yaw drive to channel the turbine rotor properly with respect to

the wind.

Nacelle: This is the housing or casing which sits on-top of the tower and includes the

gear box, low and high speed shafts, generator, controller and brakes. The rotor is

being attached to it

Tower: This is being made of steel lattice and is very high because wind speed

increase with height and taller towers enable turbines to capture more energy and

generate more electricity.

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2.1 BASIC PRINCIPLES OF WIND POWER GENERATION

Wind power is a measure of the energy available in the wind. It is a function of

the cube (third power) of the wind speed, if the wind speed is doubled, power in the

wind is increased by a factor of eight (i.e. 23) this relationship means that the small

difference in wind speed leads to a large difference in power.

Wind speed is therefore defined as the rate at which airflow past a point above

the earth’s surface.

The output of a wind turbine varies with the wind speed through the motor. The

“rated wind speed” is the speed at which the “rated power” is

achieved. This corresponds to the point at which the conversion efficiency is near its

maximum. In most system, the power output above the “rated wind speed” is

mechanically or electrically maintained at a constant level allowing more stale system

control.

The power output drops sharply at wind speed. This is better explained by the

cubic power law, which states that the power available in the wind increases eight

times from every doubling of the wind speed and decreases eight times for every

halving of the wind speed.

In a particular wind site, the power output expected at the average wind speed

can be determined by the power curve.

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10 20 30 40 50

Wind speed in MPH

POWER CURVE

FIG. 2.2

Just like the weather, the wind can be unpredictable. It varies from place to place and

from moment to moment. It is invisible and as such can only be measured with a

special instrument. While wind turbines are mostly commonly classified by their

“rated power” at certain “rated wind speed”, energy output is also greatly influenced

by some subtle features of a wind turbine’s design.

These include:

1) Cut-in-Speed: This is the minimum wind speed at which the blade will turn and

generate useable power. This wind speed is typically between 7mph and 10mph.

2) Blade Air Foil Shape: This determines the power produced at moderate speed.

When air flows past the blade a wind speed and pressure differential

created between the upper and lower surface is greater and thus acts to “lift” the blade.

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3) Tip Speed Ration (TSR): The tip-speed is the ratio of the rotation speed of the

blade to the wind speed. The larger the ratio, the faster the rotation of the wind turbine

rotor at a given wind speed.

4) Rated Speed: The rated speed is the minimum wind speed at which the turbine

will generate its designated rated power. Note that between the cut-in and rated speed,

the power output from a wind turbine increase. The rated speed for most machines is in

the range of 25mph to 30mph.

5) Cut-Out Speed: This is the wind at which the turbine may be shut down to protect

the rotor and drive train machinery from damage. A wind speed sensor is usually used

to activate the automatic brake. And normal wind operation usually resumes when the

wind drops back to a safe level.

6) Operating characters: This includes such thing as low speed on-off cycling, shut

down behavior and overall reliability. These things together determine the turbine

availability to produce power when the wind speeds are in its operating range.

7) Efficiency: The efficiency of the drive train components such as the generator,

the gear box and other can be defined as the ratio of the output to the input. It should

also be noted that the drive converts energy from one form to

8) Another. And in the process, some of the input energy/power is being consumed

to make the device operate.

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For this reason, the efficiency of the operation is defined as energy output in given a

time.

Efficiency = Energy output in a given time = Wo Energy input in the same time Win

= Power output = Po Power input Pin

9) Frequency of Operation: This is the number of cycles completed in a second.

Actually this varies from time to time. But it is necessary to stabilize it, because

as soon as the frequency is made constant, it goes a long way to influence the

power/energy output of the wind turbine.

2.2 PERFORMACE

The wind does not start as long as the “cut-in speed” has not been reached. And when

it starts it has to reach the “rated speed” i.e. the lowest speed it has to reach before it

will be able to generate its “rated power”. The turbine also shut down automatically as

soon as it gets to the “cut-off speed” to avoid damage on the turbine.

Despite the use of frequency control, the wind turbine would be permitted to

rotate at a variable speed as the wind changed. How ever since the frequency

control has to be maintained. The wind turbine rotational speed can be controlled in

two distinct positions.

1) When the wind speed is between the cut-in speed and the rated speed, the speed

can be controlled by varying the load on the generator

2) When the wind speed is between the rated and cut-off speed, it can be controlled

by changing the pitch on the turbine.

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CHAPTER THREE

LITERATURE REVIEW

3.0 TYPE OF WIND MACHINE

There are two types of wind machine (turbines) used today. This classification is

based on the direction of the rotating shaft (AXIS). Horizontal- axis wind machine

Vertical – axis wind machine. The size of wind machine varies widely. Small turbines

used to power a single home or business. This may have a capacity of 100 kilowatts.

Some large commercial sized turbines may be up to 5 million watts or 5 watts. Large

turbines are those that provide power to the electrical grid

3.1 HORIZONTAL – AXIS WIND TURBINE (HAWT)

Most wind machines being used today are the horizontal – axis type. Horizontal – axis

wind have blades like airplane propellers. A typical horizontal wind machine stands as

tall as 20 – story building and has three blades that span 20 feet across. The largest

wind machines in the world have blades longer than a football field. Wind machines

stand tall and wide to capture more wind.

The axis of rotation is parallel to the wind flow. Some very large turbine use a motor

driven mechanism that turns the machine in response to wind direction

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sensor mounted on the tower. A prime objective in wind turbine design is for the blade

to have a relatively high lift-to-drag ratio. This ratio can be varied along the length of

the blade to optimize the turbine’s energy output at various wind speeds.

Horizontal axis

Fig. 3.1

ADVANTAGES OF HAWT

1) Blades are to the side of the turbine center of gravity, helping stability.

2) Ability to wing warp, which gives the turbine blades the best angle of

attack.

3) Ability to pitch the rotor blades in a storm, to minimize damage.

4) Tall towers allow access to stronger wind in site with wind shear. It allows

placement on uneven land or in shore locations.

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5) Most of them are self-starting.

6) Can be cheaper.

DISADVANTAGES OF HAWT

1) IT has difficulty operating in near ground, turbulent winds because their

yaw and blade bearing need smoother wind flow.

2) The tall towers and long blades (up to 180feat long) are difficult to

transport.

3) Difficult to install, it needs very tall and expensive cranes and skilled

operators.

4) Their height can create local opposition based on impact to view sheds.

5) Downwind variants suffer from fatigue and structural failure caused by

turbulence.

3.2 VERTICAL AXIS WIND TURBINE (VAWT)

Vertical-axis wind machines have blades that go from top to bottom and the most

common type is (Darrien wind turbine). It looks like a giant two bladed egg beaters.

The type of vertical wind machines make up only a very small percent of the machine

used today.

Other vertical axis turbine designs include the savanis, which uses scoops to catch the

wind. A vertical axis machine need not be oriented with respect to

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wind direction because the shaft are vertical, the transmission and generator can be

mounted at the ground level allowing easier servicing and lighter weight.

Vertical axis (Darrieus Wind Turbine)

Fig. 3.2

ADVANTAGES OF VAWT

1) Easier to maintain because most of their moving part are located near the

ground.

2) As the rotor blades are vertical, a yaw drive is not needed, reducing the

need for the bearing and its cost.

3) Low height useful where laws do not permit structures to be placed high.

4) Usually have a lower tip-speed ratio so less likely to break in high winds.

5) Does not need a free standing tower so is much less expensive and

stronger in high winds that are close to the ground.

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6) In place like hilltops, ridgelines etc. we can get higher than and more powerful

winds near the ground than up high because of the speed effect of the winds moving up

a slope or funneling into a pass combining with the winds moving directly into the site.

In these places, VAWTS placed close to the ground can produce more power than

HAWTS placed higher up.

DISADVANTAGES OF VAWT

1) Most VAWTS need to be installed on relatively flat piece of land and some sites

could be too steep for them but are still usable by HAWTS.

2) A VAWT that uses guyed wires to hold it in place put stress on the bottom

bearing as all the weight of the rotor is on the bearing. Guyed wires attached to the top

bearing increase downward thrust in wind gusts solving this problem requires a

superstructure to hold top bearing in place to eliminate the downward thrusts of great

events in guyed wired models.

3) Most VAWTS are low starting torque.

3.3 POWER IN THE WIND

The power in the wind can be extracted by allowing it to blow past a moving

wing that exerts torque on a rotor. The amount of power transferred is directly

proportional to the density of the air, the area swept out by the rotor, and the cube of

the wind speed.

The power available in the wind is giving by P = 1/2 Pπ R2V3 .The mass flow of air

that travels through the swept area of a wind turbine varies with the wind speed and air

density. The kinetic energy of a given mass varies with the square of its velocity.

Because the mass flow increases linearly with the wind speed, the wind available to a

wind turbine increase as the cube of the wind speed.

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As the wind turbines extracts the energy from the air flow, the air is slowed down,

which causes it to spread out and diverts it around the wind turbine to some extent.

Windiness varies and an average value for a location does not alone indicate the

amount of energy a wind turbine could produce there. To assess the climatology of

wind speed at a particular location, a probability distribution function is often fit to the

observe data. Different locations will have different wind distribution.

Because so much power is generated by higher wind speed, much of the average

power available to a windmill canes in short bursts. Half of the energy generated

arrived in just 15% of the operating time. The consequent is that wind energy does not

have a consistent output as fuel-fired power plants.

Additional output can only be made to compensate for load increase by utilizing

advanced wind storing technologies (e.g. giant compressed air storage tank facilities).

Since wind speed is not constant, a wind generator annual energy production is

never as much as its nameplate rating multiplied by the total hours in a year. The ratio

of actual productivity in a year to the theoretical maximum is called the capacity

factor. A well-sited wind generator will have a capacity factor of about 35%. This

compares to typical capacity factors of 90% for nuclear plants, 70% for coal plants,

and 30% for oil plants.

When comparing the size of wind turbine plants to fuel power plants, it is

important to note that 1000km of wind turbine potential power would be expected to

produce as much energy in a year as approximately 500km of coal-fired generation.

Though the short term output of a wind-plant is not

completely predictable. The annual output of energy tends to vary only a few percent

points between years.

The drag type rotor, such as Savonius rotor and American Multi blade, have lower tip

to speed ratio and power coefficient compared to the lift type propeller HAWT. The

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curve from the propeller type rotor (RAWT) indicates that the rotor is able to maintain

high efficiency over a long range of rotor rpm while the sharp curve from Darreus

rotor experience drop drastically when the rotor rpm movies away from the narrow

optimum range, the Darreus rotor with low power coefficient at low tsr range indicates

a weak self-starting ability thus when the Darrius type VAWT is coupled with a low

efficiency Savonius rotor its initial stating torque is developed and also on the

alternative an induction machine could be coupled with the perils rotor to improve its

starting characteristics.

3.4 MATCHING WIND TURBINE TO LOAD

The rotor efficiency alone will not determine the efficiency of wind energy system as

the coupling of the rotor load like generators will further reduce the overall efficiency.

The power output curve for a system consisting of a rotor and generator depends not

only on the individual efficiency of both components but also how well they were

matched. The plot/curve below shows a torque of rotor at different speed.

Fig. 3.3 Relationship Between load and rotor tsr

Now considering the 6 m/s rotor torque curve and the medium load curve. When the

stationary rotor is subjected to a 6 m/s wind speed, the rotor rpm will accelerate from

zero to the rpm of the intersection between two curves and

stabilize there. The rotor will produce torque following the 6m/s curve until the rotor

torque balances with load torque at the intersection. So by plotting the, rotor torque

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curve for various speeds, the intersection of these curves will form the actual operating

rpm of the wind turbine at various wind speed. However

the rotor/load torque at different wind speed is not the actual power output, the actual

output will be lower due to losses in the generator mechanical components and

conversion losses.

Fig 3.3 shows another 2 load which is a light and heavy load A light load will cause

rotor to operate at high rpm (high tsr) which will not maximize the rotor efficiency

while the heavy load causes the rotor to rotate slowly (low tsr) which also do not

maximize the rotor efficiency. By selecting a load nearer to the rotor maximum

efficiency point like the medium curve more power can be obtained.

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CHAPTER FOUR

DESIGN SPECIFICATION FOR WIND TURBINE

4.0 STRENGTH CALCULATION FOR STRUCTURAL ANALYSIS &

SAFETY

It is usually the common practice in Engineering field to have prior knowledge of the

properties of the materials that will be used in a design so that the design could be

carried out with the awareness of the materials properties. With such prior knowledge

adequate provision could be made to compensate the inadequacies of the material

available for use in design.

It is in the light of the above that the strength calculation of these materials

must be done before and during the fabrication process. The most important test will

be the strength of wood/aluminum airfoils under centrifugal load as flying broken

pieces of airfoils are not welcomed especially in wind tunnel. The airfoils model can

be fabricated using either solid woods or aluminum sheets with spar and rib.

Having a wind turbine test model as basic of my estimates and calculation

these strength calculation/estimates can be sub-divided into.

different section as;

i) Airfoil bending stress

ii) Bolt tension at Airfoil joint and washed pressure

iii) Support arm vibration and deflection

iv) Shaft bending stress and vibration

v) Bearing size selection

vi) Pipe bending stress and vibration

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i) Airfoil Bending Stress:

Hear two main loads on the airfoils are the centrifugal force and the

aerodynamic drop force. The rough comparison of these forces shows that the

aerodynamic forces are small compared to the centrifugal force for the mode material,

solidity and operating speed. The strength property of the wood airfoils will be

supported at the centre so the centrifugal forces will cause highest stress at the centre

where the airfoils join the support arm. To test the airfoil strength both sides of the

airfoil will be loaded with dumbell weights and it will be lifted off the ground by

holding the center of the airfoils. Note that stress concentration is definitely lower

when balancing using hand instead of the actual support.

Aerodynamic force comparism to centrifugal force on the air force is thus F aero = ⅔ Pair U2 Rcl X Cnorm = ½[U2 + (wR) 2]cL Cnorm F centrifugal ½ Pwood (AL) w 2R ½ Pwood (1/2 tcl) W2R – Equation 1 The uniformity distributed centrifugal force compared to the airfoil weight = F centrifugal = m (wR)2 W R - Equation 2 mg ii) Bolt Tension at airfoil joint and washer pressure

Here each airfoil is to be supported by 4 bolts with pairs of nuts which clamp the

wood airfoil. This bolts and nuts joint will further be tightened by using spring and

plate washer. The plate washer will hopefully distribute the stress to a wider area of the

wood.

Calculation on the tension in the bolts caused mainly by an assumed airfoil

imbalance and partly by centrifugal forces showed sufficient strength.

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The wood will probably be dented in after some time of fast rotation and repeating

assembling/disassembling.

Bolt tension due to centrifugal Force

= F Atensil --Equation 3 Bolt tension and compression due to imbalance = 2Fx L H/2 --Equation 4 Atensil Total Bolt tension =Equ 3 + Equ 4 --Equation 5 Average Compression on contact Surface = F A --Equation 6 iii) Supporting Arm Vibration And Deflection

The rotor vibration might build up if the rotor rpm is operated constantly at fixed rpm

that coincide with the structure nature frequency. The rough estimate frequency is

made by assuming the support arm as a spring while the other handing components

are rigid mass and the supporting components as fixed support. This will not provide

the real structure natural frequency but just as a comparison of how stiff this part of

structure is, compared to the other parts. The pair of flat plates support arm will have

the possibility to act like a single beam which will be very stiff.

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Cantilevered beam Vibration Formula

δ = PL3 3EL --Equation 7 K = P δ --Equation 8 F = K M --Equation 9 iv) Shaft Bending Stress and Vibrating

The vibration of the shaft at hub position was analyzed as an overhanging had

with simple support beam with the rotor as a lumped mass load. This shaft in question

is supported by a pair of bearing.

Deflection of hub δ = Pa2 (1+a) 3E1 --Equation 10 Stiffness K = p δ --Equation 11 v) Pipe Bending Stress, Deflection and Vibration

The pipe supports the shaft so it will also experience the centrifugal force from

the rotor imbalance. The pipe is very stiff with very high frequency and so in the

vibrating calculation / estimation, the frame was assumed to be a fixed support while

the pipe as a cantilever supporting the rotor mass.

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vi) Bearing Size Selection

The bearing size should be as small as possible partly to reduce loss but most

importantly to reduce torque loss at start up.

4.1 SYSTEM DESIGN

Here there are two basic arrangements in respect to the system design namely:

i) Constant speed constant frequency (CSCF) system

ii) Variable speed constant frequency (VSCF) system

i) Constant speed constant frequency (CSCF) system: Is where the rotor speed is

held constant by continually adjusting blade pitch and or generator electrical

characteristics.

ii) Variable speed constant frequency (VSCF) system: Is where the rotor speed is

allowed to vary in proportion with the power resulting in maximum conversion factor

for most of the operating zone.

In the variable speed constant frequency alternators, the rotor is meant to rotate

freely at the wind speed. The actual speed of rotation is determined by these speed/load

characteristics of both wind rotor and the generator. The rotor speed determines the

efficiency of conversion from wind energy to mechanical energy. At a particular ratio

the conversion factor K1 is maximum and the efficiency of conversion from wind

energy to mechanical energy is optimum.

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Since a constant frequency is needed from a variable speed machine an

additional circuit is necessary. A solid state electronic circuit is required to rectify the

instantaneous power output d.c power and another circuit comparing chopper is used to

invert the d.c power back again to a.c at a given constant

frequency (say 50Hz). These additional circuiting makes the VSCF system more

complex and of course more cost effective.

Improvement in the design of VSCF machine has led to the development of

special type called the “Double Output Induction Generator” (DOIG). In this, the solid

state handling only the slip power and this seems an interesting comparism between

the VSCF and CSCF Systems.

The solid state electronics is used for rectification and the line commutator

inverter inverts the slip power back to alternating current. Another version of the

VSCF system has power output at modulated frequency higher than the system

frequency fs (say 50Hz) and processes it down to the system frequency, fs by the

electronic circuitry. The system uses an 8.C exited alternator having a modulated

output. So the output is an amplitude –modulated wave. The speed of the rotor of the

machine nr-Lnw

Where nw = wind speed

L = loss factor

27

Thus the output is a modulated signal consisting of (fr + fs) and (fr – fs)

components.

Fig 4.1i shows the output of a varying speed generator couple to a rectifier. The

varying frequency of the generated power is rectified and inverted again in order to

achieve a constant frequency supply. The field of the generator is excited with d.c

current.

The same process used in fig 4.1i but the field coil of the generation is excited

with alternating current at the system frequency, fs. The effect of the a.c excitation of

the field is a modulated power output with the excitation frequency as shown. Thus if

the system (excitation) frequency is 50Hz, the generator output frequency will always

be fr = + 50H2 and after the conversion to a.c, a filter network is used to removed the

rotor frequency components.

In fig 4.1iii some principle applied in fig 4, 1ii is used but the commutator above

does the operation of the rectifier, inverter and filter. Thus the a.c commutator

generator seems to be simplest methods to obtain constant frequency output from a

varying speed wind machine. Fig 4. 1iv shows a Double output induction Generator

(DOIG) where the slip frequency is derived from the slip rings. One output is derived

from the stator while the second output is derived from a line-cumulated inverter.

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Fig. 4.1ii

29

Fig. 4.1 iv

30

4.2 INTEGRATION AND CONTROL

As the need to stabilize the nation’s energy resources and electricity demand

there is a cause to improve the method of possible impact on system operation and

control.

The schedule may be implemented either electrically or by a suitable

programmed digital computer. The gain in the speed, torque and power loop controls is

schedule as a function of average wind velocity to optimize stability and response.

This inversion relates to the use of wind energy to drive a wind turbine for the

production of electrical power and specifically to a control system which automatically

modulates the pitch angle of wind turbine in order to regulate either electrical output

power, shaft torque or speed in order to minimize the effect on wind quota (a sudden,

strong, rush of air carried by wind) and turbulence (the state of being irregular or

violent movement of the air) and to reduce stress on the blades and other mechanical

components

It has been found that the control necessary to produce electrical power from a

synchronous generator, driven by a wind turbine, can be provided by varying the pitch

angle of the wind turbine blade. During start-up and short down of the wind turbine the

blade pitch angle is scheduled by open loop control as a function of rotor speed and

wind velocity. During normal operation the

31

pitch angle of the wind turbine blade is controlled in a closed loop manner to maintain

either a constant generator speed for isolated power generating station or when the

generator is synchronized to the load or constant generator output power or shaft

torque when the generator is connected to an electrical grid. This loop contains

proportional, integral and derivative control signals in addition to lead compensation.

This gain in the closed loop control is continuously varied as a function of wind

velocity to optimize stability and transient response. Wind velocity may be sensed

directly or synthesized as a function of system operation condition. The control system

for blade pitch angle is very responsive to the wind quest and reacts rapidly via an

anticipation control signal, which is summed with the close loop control signal during

rapid changes in wind conditions to minimize mechanical stress. An integration in the

closed loop is forced via a feedback loop to track the blade pitch angle even when the

closed loop controls are inactive.

32

CHAPTER FIVE

5.0 VIABILITY IN NIGERIA

Nigeria generates her electric power from two main systems the hydro and the

thermal/gas turbines. For now there are three hydro-stations in the country. These are

kanji, Jebba and Shiroro and for some reason two of the hydro – stations (Kainji and

Jebba) are built in the same river “THE RIVER NIGER”. The rest of the stations are

predominantly thermal/gas. These are Afam, Delta, Egbim, and Sapele etc

At present their capacities are shown as seen on table 1. Unfortunately the

generated power is not yet adequate for the Nation’s Power Consumers. To worsen the

situation there are lots of limitations in both transmission and distribution sectors. Such

limitations are transformers, cable’s etc and they make it difficult for the power

consumers to enjoy steady electricity supply thus most of the station and substation

were built long time ago and needed to be up-graded in other to meet the challenges of

the present day.

Most of the prospective consumers are, yet to be connected to the Nations Power

Supply System. Many towns and villages have not been privilege to see electric poles

and cable in their land, yet need electricity like others.

These brings the wind turbine generators into play and why it is likely to

succeed in Nigeria because the poor performance of the

33

“POWER HOLDING COMPANY ON NIGERIA PLC” (PHCN) disturbs the

consumers and as such those lining in good wind catchments area will not hesitate to

request for it.

Unfortunately the Nigeria populaces are still ignorant of this energy that can cost less

and yet requires no money to fuel supply system.

The wind generator can be used in remote area where erections of power lines

pose both financially problems and inconvenience due to the nature of the areas. For

examples island or areas located in or surrounded by swamps and also in small isolated

towns and village located in rocky highland scattered all over the country.

Further research on wind turbine will help to uplift our technological base. In fact,

introduction of wind turbine generator in Nigeria will help to diversify our power

source. We often hear of low water heads or over floating of the dam as causes of low

or no power supply.

Finally new areas of electric power generator should be explored (wind power

generator) if Nigeria should move forward more especially now we talk more about

technological advancement of the country.

34

5.1 ANALYSIS OF WIND RESOURCE.

The production of wind power speed maps depends on the coherent synthesis of

several pieces information. The goal of the synthesis process is to present wind power

speed value representatives of sites that are well exposed to wind.

Hilltops ridge crests mountain summits large clearing and other location free of

local obstruction to the wind are expected to have good exposure to the wind. In

contrast location in narrow valleys and canyons downwind of hills and obstruction or

in forested or urban areas likely to have poor exposure

35

TABLE 1

POWER STATION STATISTIC

Power station

Installed Capacity(MW)

Available Capacity (MW)

Actual

Generation

Kanji(H) 760 59 598

Jebba (H) 578 549 538

Shiroro (H) 600 550 200

Egbim 1320 1300 1300

Sapele 720 720 690

Ughelli 300 250 200

Afam 972 SO1) 700

Delta 912 900 830

36

5.2 IDENTIFICATION OF WIND DATA SOURCE IN NIGERIA

Unfortunately, Nigeria has only few methodological centers and the records

available so far about wind energy and speed are not so comprehensive for the three

meteorological centers considered here are Port Harcourt Bauchi and Akure; Port

Harcourt and Bauchi reading are based on Beanfort scale and wind speed were not

checked on hourly basis. This means that a lot of inaccuracies were to be expected

more when the Beaufort scale is to be converted to actual values.

While reading were taken for a period of 13 years at Bauchi center, reading were

taken for a period of 14 years at Port Harcourt centers as can be seen in Table (ii) At

Akure meteorological center reading were taken in actual value but for 2 years. The

wind data for Akure center is show in Table (iii). Unfortunately there are no

meteorological centers located in any of our beaches at Lagos, Port Harcourt, Calabar,

etc. where without any instrument; one can rate the site high in items of wind energy

and velocity.

In actual fact there is no part or position in Nigeria where the wind turbine cannot

work but there are some sites that can be used as medium or large wind plant farms

(installation). Examples of such sites are all the beaches in Nigeria and some high

lands scattered all over the country where good and steady wind flow are prominent.

37

TABLE II

Mean wind speed over all the year for Port Harcourt =2.56 m/s

Mean wind speed over all the years for Bauchi =4.78 m/s

Years

Mean wind speed (m/s)

Port Harcourt Center

Man wind speed (m/s)

Bauchi center

1949 2.16

6.38

1950

2.12 6.38

1951 2.35 -

1952 2.64 4.36

1953 2.19 5.81

1954 2.15 5.72

1955 2.17 4.55

1956 2.22 3.52

1957 2.10 3.17

1958 2.31 3.64

1959 2.02 4.52

1960 1.98 4.63

1961 2.14 5.64

1962 2.14 5.64

38

TABLE III

THE MONTHLY WIND SPEED FOR AKURE 1991 AND 1992

Month Mean wind speed

1991

Mean wind speed

1992

January 0.00 0.61

February 0.32 0.64

March 0.69 0.51

April 0.56 0.48

June 0.86 0.62

July 0.64 0.49

August 0.60 0.52

September 0.69 0.61

October 0.67 0.38

November 0.69 0.46

December 0.62 0.62

39

5.3 ADVANTAGES

The advantages that wind power generation gives are enormous

i) It relies on the renewable power of the wind which can’t be used up. That is it is

fueled by wind.

ii) These sources do not use burning fuel thus avoiding the inconveniences of

supply and the dangers that arise through their storage.

iii) Wind energy turbine doesn’t pollute the air like power plants that rely on

combustion of fossil fuel such as coal or natural gas which when burnt goes a long

polluting the atmosphere and also affecting the ozon layer.

Note that ozon layer depletion is one of the problems facing the world today and it has

been established that the cause of ozon layer depletion is the release of carbon dioxide

(CO2) through fossil fuel combustion, these means that wind energy turbine does not

produce atmospheric emission that cause acid rain.

iv) Once installed and paid for (initial cost investment) no additional cost are

originated, the electricity energy consumed is free.

v) The electricity produced is in the form of direct current and generally of

low voltage avoiding, the risk of dangerous accidents which can become

problematic with the use of conventional power lines.

vi) Wind energy can be produced in same place as it is consumed. Thus

transformer, underground cable and distribution.

40

vii) No environmental impact. This means wind does not produce waste,

fumes or smells.

viii) It is possible to use conventional electrical installation through the use

of inverters which supply AC current at 220V.

ix) Wind energy generators are one of the lowest-priced renewable energy

technologies available today.

x) Wind energy generators present the greatest advantage of being self

complimentary. On sunny days (in general with low wind) wind generators produce

electricity and on cold and windy days also which is frequently cloudy, the wind

generators will also produce electricity counting the lack of sunlight the solar energy.

41

CHAPTER SIX

CONCLUSION

As the need to stabilize the nation’s energy resource and electricity demands,

renewable energy comes into play and also at a time when customers across the

country are facing electricity rate hikes due to supply shortage, wind power is an

attractive option to consumers and business alike.

Wind energy works because it generates energy without fuel. While

providing a reliable edge against rising energy cost. Wind energy works because the

wind energy industry is a good steward of the environment and provides pollution-free,

domestically generated electricity to support our economy.

Wind energy power generators provides electricity which can be used

immediately at the point of production, used to supply isolated loads or supplied into

the national grid to alleviate and support other forms of electricity production and as

well reduce the cost of electricity.

42

To further tap this underutilized, strategic resource, a balance energy policy

should.

Remove current barriers to wind energy development in electric markets rules.

Support a long-term extension of the wind energy production tax credit to

encourage investment in the industry and

Fully tap wind energy potentials for domestic electricity production through

improved access and upgrade the existing transmission lines and creation of new ones.

Wind energy will work effectively in Nigeria’s economy, environment and energy

security and must be part of the nation’s energy policy if we are to achieve our

country’s full energy potentials.

43

REFERENCE

1. Anderson. S.P.D.L Freeman, D.L Elliott and RL George Wind Energy

Atlas Pacific Norwest Laboratory, Richland Washington 1981.

2. Anderson S.P.D, Pacific Norwest Laboratory.

3. Baker R.W and E.W Hewson Network Wind Power Over the Pacific

Norwest Bonneville Power Administration, Portland 1981.

4. Baker R.N and E.W. Hewson Network Wind Power Over the Pacific

Norwest.

5. Black and Veatch Power Plant Engineering Chapman and Hall New Yoke

1996.

6. Black and Veatch, Power Plant Engineering.

7. Eldridge F. Wind Machines Van Nostrand Reinhold 1980.

8. Eldridge F. Wine Machines.

9. Elliott D.L. Adjustment and Analysis of Data for Regional Wind Energy

Assessment Asheville, North Carolina November 12-13 1979

10. Elliott D.L, Adjustment and Analysis of Pats for Regional Wind Energy

44

11. Ezechukwu O. A Harnessing Wind Energy for Better Farm Machineries

German Alumin 1 Carl Duisbery Gessellschaft E. V Germany 26th September

2002.

12. Ezechukwu O. A. The Wind Turbine for Nigeria Power System. NSE Elect.

Div. International Conference (ICEPT) Proceeding of 12th October, 2006.

13. Kuffel L. Wind Energy Research and Demonstrative Program Wind

Characteristics- Tall Tower Study Wisconsin Power and Light. Company,

Madison Wisconsin 1982.

14. Kuffel L. Wind Energy Research and Demonstration Program Wind

Extension.

15. National Electric Power Authority (NEPA) January 2005.

16. www.windpower.co.uk

17. www.powerhorsekids.com

18. www.infowiskis.com

19. www.smartpower.org

20. www.otherpower.com