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Course Details

Objectives

Methodology

Course Contents & Day-wise Schedule

Timings & Duration

The course objective is to ensure learning on fundamentals of Wind Power Generation

Upon completion of this training one will be able to identify, distinguish and apply principles of Wind Power Generation.

Trainer-led classroom lectures giving individual attention and encouraging one- to-one and group discussions

MS-PowerPoint presentation slides to handle teaching & learning processes efficiently and effectively

Workbook containing tests and exercises to stimulate cognitive capabilities for effective learning

Familiarising Wind Power related keywords and acronyms

First Day

Orientation to Power & Energy

Conventional V/s Non-conventional Energy Sources

Wind - an Introduction

Energy Contained In Wind

Power Production from Wind

Wind Turbine Power

Second Day

Basic Components of Wind Energy Conversion System

Types of Wind Turbines

Aerodynamic Principles of Wind Turbines

Performance of Wind Turbines

Third Day

Wind data & Energy Estimation

Wind Energy Site Selection Consideration

Wind Energy, Power Generation Data

Final Test

Feedback & Conclusion

Rate of doing work(Work done / Time taken)

Independent of thetotal work to be done

Electrical power is usually measured in watt (W), kilowatt (kW), megawatt (MW)

Energy

Capacity of doing work (at certain Rate) (Power x Duration)

Energy can neither be created nor consumed nor destroyed

Energy, however may be converted or transferred to different forms

1 kWh (kilowatt hour) = 3,600,000 Joule

Everything what happens around is the expression of flow of energy in one of its forms

Energy is an important input in all sectors of any country's economy

Present Energy Crisis scenario

Population is increasing

Standard of living is increasing

Per Capita energy consumption per annum

8000 KWh in USA

150 KWh in India

USA with 7% of world's population consumes 32% of the total energy consumed in the world.

India with 20% of world's population consumes 1% of total energy consumed in the world.

Developing countries like India at present export primary products such as food,coffee, tea, jute and ores etc.

This does not give them the full value of their resources

To get better Value, the primary products should be processed to products for export

This needs energy

Energy Required (x 10 8Tonnes Eq. Of Coal)

Primary Sources of energy

Natural Gas

Nuclear (Uranium)

Secondary Sources of energy

Solar Energy

Wind Energy

Biomass Energy

Tidal Energy

Coal Oil Natural Gas Nuclear (Uranium)

Solar Energy Wind Energy Tidal Energy

Natural Gas

Water / Hydal

Agricultural & Organic wastes

Solar Energy

Wind Energy

Tidal Energy

Bio-mass / Bio-gas

Geothermal

Wind Farm of 1MW capacity saves 200 MT of Coal annually

Wind Farm of 1MV avoids emission of pollutant gases annually as under :

Sulphur dioxide2 3.2 MT

Nitrogen dioxide 1 2.4 MT

Carbon dioxide 300 500 MT

Particulate like fly ash 150 280 kgs.

Average temperature rise of around 1-3.5 0C by year 2100 a rate of warming greater than at any time over the last 10,000 years

Energy Content of Fuels GJ per tonne

North Sea Crude Oil 42.7

LPG (Liquefied Petroleum Gas: Propane, Butane) 46.0

Petrol (Gasoline) 43.8

JP1 (Jet aircraft fuel) 43.5

Diesel / Light Fuel oil 42.7

Heavy Fuel Oil 40.4

Orimulsion 28.0

Natural Gas 39.3 per 1000 Nm 3

Steam Coal 24.5

Other Coal 26.5

Straw 14.5

Wood chips 14.7

Household Waste 1995 10.0

Household Waste 1996 9.4

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CO 2-Emissions kg CO 2per GJ / kg CO 2per kg fuel

Petrol (Gasoline) 73.0 / 3.20

Diesel / Light Fuel oil 74.0 / 3.16

Heavy Fuel Oil 78.0 / 3.15

Orimulsion 76.0 / 2.13

Natural Gas (methane) 56.9 / 2.74

Coal 95.0 / 2.33 (steam coal), 2.52 (other)

What is Wind ?

Which prime source is responsible for the origin of Wind ?

Temperature Differences Drive Air circulation

The Coriolis Force

CoriolisForce Affects Global Winds

How a Wind turbine taps Wind energy ?

Windresults from Air in motion

Air in motion arises from a pressure gradient

Solar radiation heats the air near the equator

This low-density heated air is buoyed up

At the surface this air is displaced by cooler more dense higher-pressure air flowing from poles

In the upper atmosphere near the equator the air thus tend to flow back toward the poles and away from the equator.

The net result is a global convective circulation with surface winds from north to south in northern hemisphere.

Earth's rotation causes Coriolis force resulting in

an easterly wind velocity component in the northern hemisphere

Boundary layer frictional effects between the moving air and the earth's rough surface (mountains, trees, buildings and similar obstructions )

Local Winds

Differential heating of land and water. Unequal solar absorption and thermal time constants of land and water. During daylight the land heats up rapidly compared to nearby sea or water bodies and there tend to be a surface wind flow from the water to the land. At night the wind reverses, because the land surface cools faster than the water.

Hills and mountainsides. The air above the slopes heats-up during the day and cools down at night more rapidly than the air above the low lands. This causes heated air during the day to rise along the slopes and relatively cool heavy air to flow down at night

2% of all solar radiation falling on the face of earth is converted to kinetic energy of wind. 30% of this occurs in lowest 1000m elevation of the atmosphere.

Conversion of kinetic energy of wind into mechanical energy that can be utilised to perform useful work or to generate electricity.

When the wind blows against the vanes or sails they rotate about the axis and the rotational motion can be made to perform useful work.

Because wind turbines produce rotational motion, wind energy is readily converted to electrical energy by connecting the turbine to an electric generator.

Three factors determine for deriving power form wind

Wind Speed

Cross-section of wind swept by rotor

Conversion efficiency of the rotor, transmission system and generator

It is not practical to extract all of the wind's energy because the wind would have to be brought to a halt and this would prevent the passage of more air through rotor.

A 100% efficient aero-generator would therefore only be able to convert up to a maximum of around 60% of available energy in the wind into mechanical energy.

Well-designed blades will typically extract 70% of the theoretical maximum but losses incurred in conversion mechanism could decrease overall efficiency to 35% or less.

Energy available in wind is kinetic energy

Kinetic energy of any particle is equal to one half of its mass (M) times the square of its velocity (V) : P a= MV 2

The amount of air passing in unit time, through an area (A), with velocity (V) is A*V; and its mass (M) is equal to its volume multiplied by its density ( ) of air (1.225 kg/m 3at sea level) M = AV a = AV * V 2 Pa = AV 3Watts Available Wind energy is proportional to thecubeof thewind speed

Available wind energy is proportional to thecubeof the windspeed.

It is thus evident that a small increase in wind speed can have a marked effect on the power in the wind.

Wind power is also proportional to air density (1.225 kg/m 3at sea level).

It may vary 10-15% during the year because of pressure and temperature change.

It changes negligibly with water contents.

A =/4 D 2Sq. m.

The wind power is proportional to the intercept area. Thus an aero turbine with a large swept area has higher power than a smaller area machine.

Area is normally circular diameter (D) in horizontal axis machine

Available wind power

P a= /4 D 2V 3Watts

P a= /8D 2V 3Watts

This indicates that the maximum power available from the wind varies according to the square of the diameter of the wind area or square of the rotor diameter.

Thus doubling the diameter of the rotor will resulting a fourfold increase in the available power

P a= 1/8 D 2V 3Watts

Wind machines intended for generating substantial amount ofpower should havelarge rotorsand be located in areas ofhigh wind speeds.

Power coefficient (Cp), describes that fraction of the power in the wind that may converted by the wind turbine in to mechanical work

Cp =Power output from Wind Machine

Power available in wind

It is the fraction of power in a wind stream that can be extracted.

It has a theoretical maximum value of : Cp (max)= 0.593(popularly known asBetz coefficient )

P = 0.5 xx A x Cp x V 3x Ng x Nb

Where :

P = Power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)

= Air density (about 1.225 kg/m 3at sea level, less higher up)

A = Rotor swept area, exposed to the wind (m 2 )

Cp = Power coefficient (.59 {Betz limit} is the maximum theoretically possible, .35 for a good design)

V = Wind speed in meters/sec (20 mph = 9 m/s)

Ng = Generator efficiency (50% for car alternator, 80% or possibly more for a permanent magnet genertor or grid-connected induction generator. Induction generator efficiency is more than 95%)

Nb = Gearbox/bearings efficiency (depends, could be as high as 95% if good).

Where : Cp = Power coefficient

= Tip speed ratio

Also, = Rotor tip speed / Wind velocity

( =R/V )

Where = Rotational speed of rotor

R= Blade tip radius

V= Wind speed in meters/sec

Power coefficient of a rotor (Cp) is maximum for a unique Tip speed ratio ( )

What is a rotor ?

What makes the rotor turn ?

Stall and Drag

Stall Controlled Wind Turbines

Pitch Controlled Wind Turbines

Propeller Type

Horizontal Axis Type

-Single Blade Type

- Multi Blade Type

Vertical Axis Types

- Darries Type

Drag Type

-Sail Type

Vertical Axis Types

-Savonious Type

Stall Controlled

Pitch Controlled

Upwind Type

Downwind Type

Two Blade

Three Blade

Dutch Type

Multi-blade Type

-Simple in Principle

- Complex in complete conversion System

- Subjected to continuous cyclic gravity loads

- Structural Support is Critical

Vertical Axis Types

-Can be active for Wind from any direction

-Difficult to Brake

- Far Less Known

V:Wind Velocity

F W :Wind force

V T :Wind velocity due to the blade turning

F T :Torque producing component

V R :Resultant wind velocity

F R :Resultant force on the blade

a:Angle of attack

To keep the swept area perpendicular to the predominant Wind direction

Yaw Fixed

Yaw Active

Tail Vane

Yaw Error

The wind turbine is said to have a yaw error, if the rotor is not perpendicular to the wind. A yaw error implies that a lower share of the energy in the wind will be running through the rotor area.

The tower of the wind turbine carries the nacelle and the rotor.

Towers for large wind turbines may be either tubular steel towers, lattice towers, or concrete towers.

Guyed tubular towers are only used for small wind turbines (battery charges etc.)

To avoid hitting the tower at high wind speeds

The optimum height of the tower is a function of :

Tower costs per meter

How much the wind locally varies with the height above ground level, i.e. the average local terrain roughness (large roughness makes it more useful with a taller tower)

The price the turbine owner gets for an additional kilowatt hour of electricity.

Economies of scale

Larger machines are usually able to deliver electricity at a lower cost than smaller machines.

The reason is that the cost of foundations, road building, electrical grid connection, plus a number of components in the turbine (the electronic control system etc.), are somewhat independent of the size of the machine.

Maintenance Cost

Maintenance Costs are largely independent of the size of the machine.

Difficult sites Locations

In areas where it is difficult to find sites for more than a single turbine, a large turbine with a tall tower uses the existing wind resource more efficiently.

Risk distribution

Several smaller machinesspread the riskfailure

Local Electrical grid

Thelocal electrical grid may be too weakto handle the electricity output from a large machine. This may be the case in remote parts of the electrical grid with low population density and little electricity consumption in the area.

Wind Park Fluctuations

Wind fluctuations occur randomly, and therefore tend to cancel out. Again, smaller machines may be an advantage in a weak electrical grid.

Aesthetical landscape

A large machine really does not attract as much attention as many small, fast moving rotors.

The cost of using large cranes, and building a road strong enough to carry the turbine components may make smaller machines more economic in some areas.

To increase greatly the rates of rotor rotation

Chains

Fixed Ratio gears are recommended for top mounted Wind machines due to their high efficiency, known cost and minimum system risk

For ground mounted Wind machines which requires right-angle drive the transmission cost might be reduced substantially by using large diameter bearing with ring-gears mounted on the hub

If we used an ordinary generator, directly connected to a 50 Hz AC three phase grid with two, four, or six poles, we would have to have an extremely high speed turbine with between 1000 and 3000 revolutions per minute (rpm).

With a 43 m. of rotor diameter that would imply a tip speed far more than twice the speed of sound !!

Another possibility is to build a slow-moving AC generator with many poles. But it may need a 200 pole generator to arrive at a reasonable rotational speed of 30 rpm.

Another problem is, that the mass of the rotor of the generator has to be roughly proportional to the amount of torque (moment, or turning force) it has to handle. So a directly driven generator will be very heavy (and expensive) in any case.

The practical solution, which is used in the opposite direction in lots of industrial machinery, and in connection with car engines is to use a gearbox.

With a gearbox you convert between slowly rotating, high torque power which you get from the wind turbine rotor -and high speed, low torque power, which you use for the generator.

The gearbox in a wind turbine does not "change gears". It normally has a single gear ratio between the rotation of the rotor and the generator.

For a 600 or 750 kW machine, the gear ratio is typically approximately 1 to 50.

Synchronous Generators

Asynchronous Generators

Direct Grid connection

Indirect Grid connection

Constant Speed frequency (CSCF)

Large Generator Connected to Grid

Variable Speed constant frequency (VSCF)

Small generators for autonomous application

Variable Speed variable Frequency (VSVF)

Stand alone power application

Basis of Operation

Constant Tip Speed

Constant Tip Speed ratio

Wind Power Rating

Type of the Load (Battery, Grip, Inverter etc.)

Small Generator ( =< 100 kW )

- Permanent Magnet, DC Generators

Medium Generator ( =< 1000 kW )

- DC Generator, Synchronous Generator,Asynchronous Generator

Large Generator ( >= 1000 kW )

- Induction Generator

Machine Availability Hours Number of hours WTG is available without any breakdown / problem for power generation

Grid Availability Hours Number of hours state electricity board common grid is available.

Export of Power kWh KWh exported to the grid and metered at Electricity Board (Tri-vector Meter). These units will be billed for further commercial proceedings.

Import of Power kWh KWh consumed by WTG components like space heater, fan, yaw motor, hydraulic pump motor etc. from the grid.

Export of k VARh Reactive Power supplied to grid e.g. over compensation.

Import of kVARh Reactive power drawn from Grid e.g. for magnetizing current of generator (These units of kVARh charged as penalty to the owner by State Electricity Board at a rate decided by respective SEBs)

The wind turbine generator converts mechanical energy to electrical energy.

Wind turbine generators are a bit unusual, compared to other generating units you ordinarily find attached to the electrical grid.

One reason is that generator has to work with a power source (the wind turbine rotor) which supplies very fluctuating mechanical power (torque).

Electro-magnetism

Flemings Right-hand Rule

F = PN / 120

Vrms / phase = 2.22 x F x Z x

Synchronous Generators Synchronous generators have their own DC excitation system and hence can work with or without grid supply

Asynchronous Generators Induction generators require excitation power from the grid and hence cannot work without grid supply.

If the magnet is forced around, it is discovered that it sends alternating current into the STATOR windings.

It requires more powerful magnet or more stator conductors to produce much electricity.

It requires a constant rotational speed in order to produce alternating current with a constant frequency

The reason why it is called asynchronousGenerator is that the magnet in the centre will rotate at a constant speed which is synchronous with (running exactly like the cycle in) the rotation of the magnetic field.

Consequently, with this type of generator you will normally want to use anindirect grid connectionof the generator.

All 3-phase generators use a rotating field.

The fluctuation in magnetism corresponds exactly to the fluctuation in voltage of each phase.

When one phase is at its peak, the other two have the current running in the opposite direction, at half the voltage.

Since the timing of current in the three magnets is one third of a cycle apart, the magnetic field will make one complete revolution per cycle.

With a 50 Hz grid, the needle will make 50 revolutions per second,i.e. 50 times 60 = 3000 rpm (revolutions per minute).

In practice, permanent magnet synchronous generators are not used very much.

There are several reasons for this.

One reason is that permanent magnets tend to become de-magnetized by working in the powerful magnetic fields inside a generator.

Another reason is that powerful magnets (made of rare earth metals, e.g.Neodynium) are quite expensive, even if prices have dropped lately.

Wind turbines which use synchronous generators normally use electromagnets in the rotor which are fed by direct current from the electrical grid.

Since the grid supplies alternating current, they first have to convert alternating current to direct 1 current before sending it into the coil windings around the electromagnets in the rotor.

If we double the number of magnets in the Rotor, however, we can ensure that the magnetic field rotates at half the speed.

This generator has four poles at all times, two South and two North. Since a four pole generator will only take half a revolution per cycle, it will obviously make 25 revolutions per second on a 50Hz grid, or 1500 revolutions per minute (rpm).

When we double the number of poles in the Stator of a synchronous generator we will have to double the number of magnets in the Rotor, as you see on the picture. Otherwise the poles will not match.

Most wind turbines in the world use a so-called three phase asynchronous (cage wound) generator

Also called aninduction generatorto generate alternating current.

This type of generator is not widely used outside the wind turbine industry, and in small hydropower units

It is the rotor that makes the asynchronous generator different from thesynchronous generator.

The rotor consists of a number of copper or aluminum bars which are connected electrically by copper or aluminum end rings, as you see in the picture to the right.

The rotor is provided with an "iron" core, using a stack of thin insulated steel laminations, with holes punched for the conducting aluminum bars.

The rotor is placed in the middle of the stator, which in this case, once again, is a 4- pole stator which is directly connected to the three phases of theelectrical grid.

When the current is connected, the machine will start turning like a motor at a speed which is just slightly below the synchronous speed of the rotating magnetic field from the stator.

If we look at the rotor bars from above we have a magnetic field which moves relative to the rotor. This induces a very strong current in the rotor bars which offer very little resistance to the current, since they are short circuited by the end rings.

The rotor then develops its own magnetic poles, which in turn become dragged along by the electromagnetic force from the rotating magnetic field in the stator.

Now, what happens if we manually crank this rotor around at exactly the synchronous speed of the generator, e.g. 1500 rpm

Nothing. Since the magnetic field rotates at exactly the same speed as the rotor, we see no induction phenomena in the rotor, and it will not interact with the stator.

But if we increase speed above 1500 in the rotor. The harder you crank the rotor, the more power will be transferred as an electromagnetic force to the stator, and in turn converted to electricity which is fed into the electrical grid.

The speed of the asynchronous generator will vary with the turning force (moment, or torque) applied to it. In practice, the difference between the rotational speed at peak power and at idle is very small, about 1 per cent. This difference in per cent of thesynchronous speed , is called the generator's slip.

Thus a 4-pole generator will run idle at 1500 rpm if it is attached to a grid with a 50 Hz current. If the generator is producing at its maximum power, it will be running around 1510 rpm

It is a very useful mechanical property that the generator will increase or decrease its speed slightly if the torque varies.

Why Induction Generators ?

The feature of stand alone is not advantageous. Power is not required in remote areas where normally windmills are installed. It has to be fed into the grid.

Induction Generators are :

Moresuitable for the highly fluctuating power input.

Simple and rugged in construction (no excitation)

Less in weight and cost

Reliable in operation

Very little maintenance

The advantage of indirect grid connection is that it is possible to run the wind turbine at variable speed.

Disadvantages of Indirect Grid Connection is cost . The turbine will need a rectifier and two inverters, one to control the stator current, and another to generate the output current.

Other disadvantages are the energy lost in the AC-DC- AC conversion process

The power electronics may introduce harmonic distortion of the alternating current in the electrical grid, thus reducing power quality. The problem of harmonic distortion arises because the filtering process mentioned above is not perfect, and it may leave some "overtones" (multiples of the grid frequency) in the output current.

Wind speedsare usually measured as 10 minute averages

Wind roses :vary from one location to the next As an example, take a look at this wind rose : Although the primary wind direction is the same, Southwest, you will notice that practically all of the wind energy comes from West and Southwest, so on this site we need not concern ourselves very much about other wind directions.

Isovents : Contours of constant average wind velocity, (Monthly / Quarterly / Yearly average )

Isodynes : Contours of constant wind power ( Watts / m3 of the area@ perpendicular to thewind flow )

Seasonal Changes (magnitude & direction)

Instantaneous changes (magnitude & direction)

Factors which affect the nature of the wind close to the surface of the earth

Latitude of the place

Altitude of the place

Topography of the place

Scale of the hour, month or year

Hourly mean Wind velocity basic data (for many years), provides the data for establishing the potential of the place for tapping the wind energy.

The scale of the month is useful to indicate whether it is going to be useful during particular periods of the year.

The data based on scale of the hour is useful for mechanical aspects of design.

Hourly Mean wind velocity

Scale of month

Scale of hour

Spell of low wind speeds (for alternatives / storage)

Gusts ( structural design, safety measures )

High annual average wind speed Strategy for siting-

Survey of historical wind data

Contour maps of terrain and wind are consulted

Potential sites are visited - Best sites are visited

Best sites are instrumented for one year

Availability of anemometer data

Availability of wind velocity curve at the proposed site to predict the electrical power

Wind Structure at the proposed site, for knowing departure from homogeneous flow of the wind in direction and velocity.

Altitude of the proposed site to examine the air density and power in wind.

Terrain and its aerodynamics

Local ecology; bare rock, trees, grass, vegetation etc.

Distance to roads or Railways

Distance to local users , transmission line length, losses, costs

Nature of ground for foundations, corrosions

Favorable land cost

Site ambient parameters - temperature, dust, humidity, icing, salt spray etc.

Best sites are found off-shore and at sea coast. Average 2400 kWh / m 2per year

Second preference can be the sites in mountains. Average 1600 kWh / m 2per year.

The characteristics of a good wind power site :

The site should have a high annual wind speed

There should be no tall obstructions for a radius of 3 km.

An open plain or an open shore line may be a good location

The top of a smooth, well rounded hill with gentle slopes laying on a flat plain or located on an island in a lake or sea.

A mountain gap which produces to wind tunneling is good

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