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Transcript

  • 1.  
  • 2. Introduction
    • Course Details
      • Objectives
      • Methodology
      • Course Contents & Day-wise Schedule
      • Timings & Duration
  • 3. Course Objective
    • 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.
  • 4. Methodology
    • 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
  • 5. Day-wise Schedule
    • First Day
      • Orientation to Power & Energy
      • Conventional V/s Non-conventional Energy Sources
      • Break
      • Wind - an Introduction
      • Energy Contained In Wind
      • Power Production from Wind
      • Wind Turbine Power
  • 6. Day-wise Schedule
    • Second Day
      • Basic Components of Wind Energy Conversion System
      • Types of Wind Turbines
      • Break
      • Aerodynamic Principles of Wind Turbines
      • Performance of Wind Turbines
  • 7. Day-wise Schedule
    • Third Day
      • Wind data & Energy Estimation
      • Wind Energy Site Selection Consideration
      • Wind Energy, Power Generation Data
      • Break
      • Final Test
      • Feedback & Conclusion
  • 8. Recalling the Fundamentals
    • Power
      • Rate of doing work (Work done / Time taken)
      • Independent of the total 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
  • 9. Energy
    • 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
  • 10. Energy
    • 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.
  • 11. Energy
    • 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
  • 12. Growth of Energy Requirement
    • Energy Required (x 10 8 Tonnes Eq. Of Coal)
  • 13. Sources of Energy
    • Primary Sources of energy
      • Coal
      • Oil
      • 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
  • 14. Commercial / Conventional Energy Sources
    • Coal
    • Oil
    • Natural Gas
    • Water / Hydal
    • Agricultural & Organic wastes
    Source: www.eia.doe.gov 0.3% Waste 1.2% Dung 8% 6.6% Wood 2.0% Hydro 0.13% Uranium 92% 19.0% Gas 38.5% Oil 32.5% Coal Total Energy Consumption Source
  • 15. Non-commercial / Non-conventional Energy Sources
    • Solar Energy
    • Wind Energy
    • Tidal Energy
    • Bio-mass / Bio-gas
    • Geothermal
  • 16. Non-commercial / Non-conventional Energy Sources Several multiple megawatt wind turbines are in operation and many more are in construction. There are number of small wind turbines and wind Pumps in use. Electricity Mechanical Energy (Pumping Transport) Wind The kinetic energy Millions of solar water heaters and solar cookers are in use. Solar cells and Power Towers are in operation. Low temperature heat (Space heating water heating and electricity) Solar Total solar radiation absorbed by the earth and its atmosphere is 3.8 x 10 24 J/Yr. Comment From / Application Resource
  • 17. Non-commercial / Non-conventional Energy Sources There are million of biogas plants in operation, most of them are in China. Bio-gas (Cooking, mechanical power etc.) The world’s standing bio-mass has a energy content of about 1.5X10 22 J Biomass (principally wood accounts for about 15% of the world’s (commercial fuel) Consumption; It provides over 80% of the energy needs of many developing countries. High temperature heat (Cooking, Smelting) Biomass Total solar radiation absorbed by plants is 1.3X10 21 J/Yr Comment From / Application Resource
  • 18. Non-commercial / Non-conventional Energy Sources Installed capacity Is more than 2500 MW but output is expected to Increase more than seven fold by 2000. Electricity The total amount of heat stored in water or steam to a depth of 10 km is estimated to be 4 X 10 21 J that stored In the First 10 km of dry rock Is around 10 27 J/yr Geothermal energy supplies about 5350 MW of heat for use in bathing principally in Japan, but also in Hungary Ice land and Italy. More than one lakh houses are supplied with heat from geothermal wells. The installed capacity is more than 2650 MW (thermal) Low temperature heat (Bathing space and water heating) Geothermal The heat flux from the Earth's interior through the surface is 9.5 X 10 20 J/Yr. Comment From / Application Resource
  • 19. Non-commercial / Non-conventional Energy Sources The Japanese wave energy research vessel, the Kaimel. has an Installed capacity of about 1 MW. There are In addition several hundred waves powered navigational buoys designs after large prototype Electricity Wave The amount of energy stored as Kinetic Energy in weaves may be of the order of 10 18 J Only one large tidal barrage is in operation (In France) and three are small schemes In Russia and China total Installed. Capacity is about 240 MW and the out put around OS TWh/Yr. In addition China has several small tidal pumping stations. Electricity Tidal Energy dissipated In connection with slowing down the rotation of the earth. Comment From / Application Resource
  • 20. Non-commercial / Non-conventional Energy Sources Large hydro schemes provide about one quarter of worlds total electricity supply and more than 40% of the electricity used in developing counties. The installed capacity is more than 363GW. The technically usable Potential is estimated to be 2215GW or 19000 TWh/Yr There are no accurate estimates of the number of capacity of small hydro-plants currently in operation. Electricity Hydro The annual precipitation land amounts to about 1.1 x 10 17 Kg. of water. Taking the average elevation of land area as 840 m. The annually accumulated potential energy would be 9 x 10 20 J Comment From / Application Resource
  • 21. Economies of Wind Power Wind Power cost v/s conventional Power Cost Years of Operation
  • 22. Green Power
    • Wind Farm of 1MW capacity saves 200 MT of Coal annually
    • Wind Farm of 1MV avoids emission of pollutant gases annually as under :
      • Sulphur dioxide 2 – 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 0 C by year 2100 – a rate of warming greater than at any time over the last 10,000 years
  • 23.
    • 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
    • -------------------------------------------------------------------------------------------------------------------------------------------------
    • CO 2 -Emissions kg CO 2 per GJ / kg CO 2 per 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)
    Green Power
  • 24. Wind
    • What is Wind ?
    • Which prime source is responsible for the origin of Wind ?
    • Temperature Differences Drive Air circulation
    • The Coriolis Force
    • Coriolis Force Affects Global Winds
    • How a Wind turbine taps Wind energy ?
    Coriolis Force
  • 25.
    • Wind results 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.
    Wind
  • 26. Wind is much more complex due to:
    • 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.
    Diurnal (Night and Day) Variations of the Wind
  • 27. Wind Energy use
    • 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.
    Wind Turbines Deflect the Wind
  • 28. The power from wind
    • 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
  • 29.
    • 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.
    The power from wind Mean (Average) Power of the Wind
  • 30. Energy contained in Wind
    • 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 = ½ 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 3 at sea level) M =  AV a = ½  AV * V 2 Pa = ½  AV 3 Watts Available Wind energy is proportional to the cube of the wind speed
  • 31. Energy contained in Wind
    • Available wind energy is proportional to the cube of the wind speed.
    • 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 3 at sea level).
    • It may vary 10-15% during the year because of pressure and temperature change.
    • It changes negligibly with water contents.
  • 32. Power Production from Wind
    • A =  /4 D 2 Sq. 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 = ½   /4 D 2 V 3 Watts
    • P a =  /8  D 2 V 3 Watts
    • 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 2 V 3 Watts
    • Wind machines intended for generating substantial amount of power should have large rotors and be located in areas of high wind speeds.
  • 33. Power Coefficient
    • 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 as Betz coefficient )
  • 34. Power Generated and wind Speed
  • 35. Wind Turbine Power
    • P = 0.5 x  x A x Cp x V 3 x Ng x Nb
    • Where :
    • P = Power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
    • = Air density (about 1.225 kg/m 3 at 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).
  • 36. Cp /  Relationship
    • Cp α  2
    • 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 (  )
  • 37. Basic Components of a Wind Turbine Aero Turbine Gearing Coupling Electric Generator Wind Output Power Controller Yaw Control & Pitch control Wind Speed & Direction Speed Speed & Torque
  • 38.
    • What is a rotor ?
    • What makes the rotor turn ?
    • Stall and Drag
    • Stall Controlled Wind Turbines
    • Pitch Controlled Wind Turbines
    Aerodynamic Principles of Wind Turbines
  • 39. Types of Wind machines
    • Propeller Type
    • Horizontal Axis Type
    • - Single Blade Type
    • - Multi Blade Type
    • Vertical Axis Types
    • - Darries Type
    • Drag Type
    • Horizontal Axis 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
    Savonious Type Downwind Type Darries Type Three Blade Two Blade
  • 40. Characteristics of Wind Machines
    • Horizontal Axis 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
  • 41. Forces acting on the Blade
    • 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
    F W F R F T a V T V R Plane of Rotation V
  • 42. Performance of Wind Machines
  • 43. Yaw Control
    • 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.
  • 44. Wind Turbine Towers
    • 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.)
    Tubular Tower Lattice Tower Concrete Tower Guyed Tubular Tower
  • 45. Blade & Tower
    • To avoid hitting the tower at high wind speeds
    1.5 m. gap as per international compliance 5 0 tilt Rotor Blades Lift Direction
  • 46. Choosing between low and tall Towers
    • 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.
  • 47. Reasons for Choosing Large Turbines
    • 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.
  • 48. Reasons for Choosing Smaller Turbines
    • Risk distribution
      • Several smaller machines spread the risk failure
    • Local Electrical grid
      • The local electrical grid may be too weak to 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.
    • Cost
      • 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.
  • 49. Wind Machine Transmission
    • To increase greatly the rates of rotor rotation
      • Gears
      • Chains
      • Belts
    • 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
  • 50. Why to use a Gearbox ?
    • 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.
    `
  • 51. Gearbox : Less Torque, More Speed
    • 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.
  • 52. Choice of Generators and Evacuation
    • Synchronous Generators
    • Asynchronous Generators
    • Direct Grid connection
    • Indirect Grid connection
  • 53. Wind Machine Electrical Generating Schemes
    • 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
  • 54. Wind Machine Electrical Generating Systems
    • 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
  • 55. Key Parameters of Wind Turbine 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.
  • 56. Key Parameters of Wind Turbine Generator
    • 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)
  • 57. Electrical Generators used in WTGs
    • 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).
  • 58. Basics of Electrical Power Generation
    • Electro-magnetism
    • Fleming’s Right-hand Rule
    • F = PN / 120
    • Vrms / phase = 2.22 x F x Z x 
    N S
  • 59. Choice of Generators
    • 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.
  • 60. Synchronous Generators
    • 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
  • 61. Synchronous Generators
    • The reason why it is called a synchronous Generator 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 an indirect grid connection of the generator.
  • 62. Synchronous Generators
    • 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).
  • 63. Synchronous Generators
    • 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.
    Grid Connection of Offshore Wind Parks
  • 64. Synchronous Generators
    • 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.
  • 65. Asynchronous Generators
    • Most wind turbines in the world use a so-called three phase asynchronous (cage wound) generator
    • Also called an induction generator to generate alternating current.
    • This type of generator is not widely used outside the wind turbine industry, and in small hydropower units
  • 66. Asynchronous Generators (Induction Generator)
    • It is the rotor that makes the asynchronous generator different from the synchronous 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 &quot;iron&quot; 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 the electrical grid.
  • 67. Asynchronous Generators (Induction Generator)
    • 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.
  • 68. Asynchronous Generators (Induction Generator)
    • 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 the synchronous speed , is called the generator's slip.
  • 69. Asynchronous Generators (Induction Generator)
    • 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.
  • 70. Asynchronous Generators (Induction Generator)
    • 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 :
    • More suitable for the highly fluctuating power input.
    • Simple and rugged in construction (no excitation)
    • Less in weight and cost
    • Reliable in operation
    • Very little maintenance
  • 71. Indirect Grid connection of Wind Turbines Rotor, Gearbox, and Generator Variable Direct Irregular Grid Frequency Current Switched Frequency AC (DC) AC AC
  • 72. Indirect Grid Connection : Variable Speed
    • 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 &quot;overtones&quot; (multiples of the grid frequency) in the output current.
  • 73. Wind Data and Energy Estimation
    • Why?
    • Wind speeds are 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 the wind flow )
    • Seasonal Changes (magnitude & direction)
    • Instantaneous changes (magnitude & direction)
  • 74. Wind Data and Energy Estimation
    • 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
  • 75. Wind Data and Energy Estimation
    • 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 )
  • 76. Site Selection Consideration
    • 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
    Anemometer
  • 77. Site Selection Consideration
    • 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.
  • 78. Site Selection Consideration
    • Best sites are found off-shore and at sea coast. Average 2400 kWh / m 2 per year
    • Second preference can be the sites in mountains. Average 1600 kWh / m 2 per year.
  • 79. The Characteristics of a good Wind Power site
    • 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
  • 80. Wind Energy Worldwide World Leaders in Wind Capacity December 2003   Country Capacity (MW)   Germany 14,609   United States 6,374   Spain 6,202   Denmark 3,110   India 2,110   Netherlands 912   Italy 904   Japan 686   United Kingdom 649   China 568
  • 81. Wind Energy Potential in India State-wise Power Installed Capacity in India (As on 31 st December, 2003) Source: MNES
  • 82. Wind Energy in India Source: MNES
  • 83. Wind Power Projects Source: MNES
  • 84. Wind Energy Potential & Installation (State-Wise) Source: MNES
  • 85. Wind Energy Potential & Installation (State-Wise) Source: MNES
  • 86. Question & Answer Session
  • 87. Thank You Basics of Wind Energy THE END

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