Published on March 27, 2014
Wind Power A PRIMER ON wind electric systems
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CEESAT NOTES 3 From wind to electricity. 10 to 50 m High above GL, Turn turbine and generator, make electricity! Wind resources: assessment, monitoring, site selection Energy conversion: wind turbine, gear[?], generator, control Tower : support at 50 m height with a strong structure.
CEESAT NOTES 4 wind energy conversion systems (WECs) Design and successful operation of wind energy conversion systems (WECs) is a very complex task and requires many interdisciplinary skills, e.g., civil, mechanical, electrical and electronics, geography, aerospace, environmental etc. Yet success has been achieved...
CEESAT NOTES 5 Performance of WECS The availability of wind resources are governed by the climatic conditions of the region concerned for which wind survey is extremely important to exploit wind energy. Performance of W E C S depends upon: Subsystems like wind turbine (aerodynamic), gears (mechanical), generator (electrical) and Control (electronic)
CEESAT NOTES 6 Potential in India : Gross Potential :- 45,000 MW Technical Potential :- 13,000 MW Sites with Annual Average Wind Power Density > 200 watts/m2 generally viable, 208 such sites in 13 states identified States with high potential : Gujarat, Andhra Pradesh, Tamil Nadu, Karnataka, Kerala, Madhya Pradesh, and Maharashtra.
CEESAT NOTES 7 India’s Installed Wind Power Gen Capacity at end of 2001 State Installed capacity, MW Tamil nadu 828 Maharastra 236 Gujarat 167 Andhra 92 Karnataka 50 M.P. 23 All Others 111
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CEESAT NOTES 9 Wind resources Apart from having a good wind turbine, the most critical aspects for the success of investment in the wind energy sector are having a good site and an accurate assessment of the wind resource at the site.
CEESAT NOTES 10 Wind Resource Monitoring Site selection Wind Monitoring Wind Resource Mapping
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CEESAT NOTES 13 anemometer An instrument for measuring the force or velocity of wind. There are various types: A cup anemometer, is used to measure the wind speed from the speed of rotation of a windmill which consist of 3 or 4 hemispherical or conical cups, each fixed to the ends of horizontal arms attached to a vertical axis. A Byram anemometer is a variety of cup anemometer.
CEESAT NOTES 14 A counting anemometer has cups or a fan whose rotation is transmitted to a counter which integrates directly the air movement speed. A hand anemometer is small portable anemometer held at arm's length by an observer making a wind speed measurement. A pressure tube anemometer (Dines anemometer) is an instrument that derives wind speed from measurements of the dynamic wind pressures. Wind blowing into a tube develops a pressure greater than the static pressure, while wind blowing across a tube develops a pressure less than the static. This pressure difference is proportional to the square of the wind speed.
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CEESAT NOTES 16 Hurricane12>34 m/s (>65 knots) 1129-34 m/s (56-65 knots) Strong Gale1025-29 m/s (48-56 knots) Gale921-25 m/s (41-48 knots) Gale817-21 m/s (34-41 knots) Strong714-17 m/s (28-34 knots) Strong611-14 m/s (22-28 knots) Fresh58.5-11 m/s (17-22 knots) Moderate45.8-8.5 m/s (11-17 knots) Light33.6-5.8 m/s (7-11 knots) Light21.8-3.6 m/s (3.5-7.0 knots) Light10.4-1.8 m/s (0.9-3.5 knots) Calm00.0-0.4 m/s (0.0-0.9 knots) SCALE Wind SPEED Beaufort scale WIND Wind Speed at 10 m height
CEESAT NOTES 17 Some definitions…. 1 m/s = 3.6 km/h = 2.237 mph = 1.944 knots 1 knot = 1 nautical mile per hour = 0.5144 m/s = 1.852 km/h = 1.125 mph average wind speed: The mean wind speed over a specified period of time. PITCH CONROL: A method of controlling the speed of a wind turbine by varying the orientation, or pitch, of the blades, and thereby altering its aerodynamics and efficiency.
CEESAT NOTES 18 For wind data from selected stations, essential attributes are: Station location Local topography Anemometer height and exposure Type of observation (instantaneous or average) Duration of record.
CEESAT NOTES 19 Topographic maps provide the analyst with a preliminary look at other site attributes, including: Available land area Positions of existing roads and dwellings Land cover (e.g., forests) Political boundaries Parks Proximity to transmission lines.
CEESAT NOTES 20 For verifying site conditions items of importance include: Available land area Land use Location of obstructions Trees deformed by persistent strong winds (flagged trees) Accessibility into the site Potential impact on local aesthetics Cellular phone service reliability for data transfers Possible wind monitoring locations.
CEESAT NOTES 21 WIND RESOURCE ASSESSMENT- in India- Implemented through : (i) State Nodal Agencies (ii) Centre for Wind Energy Technology (C- WET) Financial Assistance : (i) Full establishment costs of Wind Resource Assessment Project (WRAP) of C-WET by the Central Government.
CEESAT NOTES 22 WIND RESOURCE ASSESSMENT Implemented through…. : (ii) The cost of setting up the wind monitoring stations would be shared between MNES and State Nodal agencies in 80:20 ratio, except for North-eastern and hilly States, where it would be in 90:10 ratio.
CEESAT NOTES 23 Resource Survey in India Published databases Centre for Wind Energy Technology (C-WET) Chennai. 6 Volumes of “Wind Energy –Resource Survey in India” , containing wind data have been published Master Plans for 87 sites prepared and available from C-WET at nominal cost. Wind data available from C-WET on CD ROM.
CEESAT NOTES 24 Government of India Ministry of New and Renewable Energy (Wind Power Division) Block No.14, CGO Complex, Lodhi Road, New Delhi – 110003 •C-WET would evaluate the eligibility of manufacturer, who approaches for Type. Certification, as per the evaluation criteria in vogue, which is being followed by C- WET. •Validity of Self-Certification facility for models specified in the List of Models and Manufacturers thereof issued by C- WET is extended up to 30th September, 2007. •Self-Certification facility would be available for a maximum period of 18 months from the date of signing of the agreement with C-WET for the models hereinafter including in the category "Model under Testing and Certification at C-WET" in the List to be issued by C-WET.
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CEESAT NOTES 32 Choosing an exact location for the monitoring tower: Place the tower as far away as possible from local obstructions to the wind Select a location that is representative of the majority of the site.
CEESAT NOTES 33 Wind energy basics Kinetic energy > Mechanical [Rotational] > Electrical energy Wind is created by the unequal heating of the Earth’s surface by the sun. Wind turbines convert the kinetic energy in wind into mechanical power that runs a generator to produce electricity.
CEESAT NOTES 34 Horizontal Axis upwind Wind Turbine Most turbines today are Horizontal Axis upwind machines with two or three blades, made of a composite material like fiberglass.
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CEESAT NOTES 36 •The amount of power a turbine will produce depends primarily on the diameter of its rotor. •The diameter of the rotor defines its “swept area,” or the quantity of wind intercepted by the turbine. •The turbine’s frame is the structure onto which the rotor, generator, and tail are attached. The tail keeps the turbine facing into the wind.
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CEESAT NOTES 39 Small WECS for Pumping Water ‘off grid’ One- to 10-kW turbines can be used in applications such as pumping water. Wind-electric pumping systems can be placed where the wind resource is the best and connected to the pump motor with an electric cable.
CEESAT NOTES 40 Small wind turbines Usually machines under about 10 kW in output. In developing countries small wind turbines are used for rural energy applications, and there are many "off-grid" applications in the developed world as well - such as providing power for navigation beacons. Since most are not connected to a grid, many use DC generators and run at variable speed. A typical 100 W battery-charging machine has a shipping weight of only 15 kg
CEESAT NOTES 41 The formula for calculating the power from a wind turbine is:
CEESAT NOTES 42 As the wind turbine extracts 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. Albert Betz, a German physicist, determined in 1919 (see Betz' law) that a wind turbine can extract at most 59% of the energy that would otherwise flow through the turbine's cross section. The Betz limit applies regardless of the design of the turbine.
CEESAT NOTES 43 Operating Characteristics All wind machines share certain operating characteristics, such as cut-in, rated and cut- out wind speeds. Cut-in Speed Cut-in speed is the minimum wind speed at which the wind turbine will generate usable power. This wind speed is typically between 7 and 10 mph. Rated Speed The rated speed is the minimum wind speed at which the wind turbine will generate its designated rated power. For example, a "10 kilowatt" wind turbine may not generate 10 kilowatts until wind speeds reach 25 mph. Rated speed for most machines is in the range of 25 to 35 mph.
CEESAT NOTES 44 Rated Speed… At wind speeds between cut-in and rated, the power output from a wind turbine increases as the wind increases. The output of most machines levels off above the rated speed. Most manufacturers provide graphs, called "power curves," showing how their wind turbine output varies with wind speed.
CEESAT NOTES 45 Cut-out Speed At very high wind speeds, typically between 45 and 80 mph, most wind turbines cease power generation and shut down. The wind speed at which shut down occurs is called the cut-out speed. Having a cut-out speed is a safety feature which protects the wind turbine from damage. Shut down may occur in one of several ways. In some machines an automatic brake is activated by a wind speed sensor.
CEESAT NOTES 46 Cut out speed & yaw Some machines twist or "pitch" the blades to spill the wind. Still others use "spoilers," drag flaps mounted on the blades or the hub which are automatically activated by high rotor rpm's, or mechanically activated by a spring loaded device which turns the machine sideways to the wind stream. Normal wind turbine operation usually resumes when the wind drops back to a safe level.
CEESAT NOTES 47 Tip Speed Ratio The tip-speed is the ratio of the rotational speed of the blade to the wind speed. The larger this ratio, the faster the rotation of the wind turbine rotor at a given wind speed. Electricity generation requires high rotational speeds. Lift-type wind turbines have maximum tip-speed ratios of around 10
CEESAT NOTES 48 number of blades The number of rotor blades and the total area they cover affect wind turbine performance. For a lift- type rotor to function effectively, the wind must flow smoothly over the blades. To avoid turbulence, spacing between blades should be great enough so that one blade will not encounter the disturbed, weaker air flow caused by the blade which passed before it. It is because of this requirement that most wind turbines have only two or three blades on their rotors
CEESAT NOTES 49 Transmission The number of revolutions per minute (rpm) of a wind turbine rotor can range between 40 rpm and 400 rpm, depending on the model and the wind speed. Generators typically require rpm's of 1,200 to 1,800. As a result, most wind turbines require a gear-box transmission to increase the rotation of the generator to the speeds necessary for efficient electricity production.
CEESAT NOTES 50 Electrical Generators It converts the turning motion of a wind turbine's blades into electricity. Inside this component, coils of wire are rotated in a magnetic field to produce electricity. Different generator designs produce either alternating current (AC) or direct current (DC),
CEESAT NOTES 51 generators for wind turbines At the present time and for the near future, generators for wind turbines will be synchronous generators, permanent magnet synchronous generators, and induction generators, including the squirrel-cage type and wound rotor type.
CEESAT NOTES 52 generators for SMALL wind turbines For small to medium power wind turbines, permanent magnet generators and squirrel- cage induction generators are often used because of their reliability and cost advantages. Induction generators, permanent magnet synchronous generators, and wound field synchronous generators are currently used in various high power wind turbines.
CEESAT NOTES 53 range of output power ratings. Generators are available in a large range of output power ratings. The generator's rating, or size, is dependent on the length of the wind turbine's blades because more energy is captured by longer blades.
CEESAT NOTES 54 Range of power <100 kW 101 kW - 250 kW 251 kW - 500 kW 501 kW - 750 kW 750 kW - 1000 kW 1001 kW - 2000 kW >2000 kW
CEESAT NOTES 55 Applications adapted to run on DC. • Storage systems using batteries store DC and usually are configured at voltages of between 12 volts and 120 volts in USA. A typical 100 W battery-charging machine has a shipping weight of only 15 kg.
CEESAT NOTES 56 A .C. Generators….. • Generators that produce AC are generally equipped with features to produce the correct voltage (120 or 240 V) and • constant frequency (60 / 50 cycles) of electricity, even when the wind speed is fluctuating.
CEESAT NOTES 57 Advantages of Induction generator over synchronous Induction generator offers many advantages over a conventional synchronous generator as a source of isolated [A .C] power supply. Reduced unit cost, ruggedness, brush less (in squirrel cage construction), reduced size, absence of separate DC source and ease of maintenance, self-protection against severe overloads and short circuits, are the main advantages
CEESAT NOTES 58 induction generator… Further induction generators are loosely coupled devices, i.e. they are heavily damped and therefore have the ability to absorb slight change in rotor speed and drive train transient to some extent can therefore be absorbed.
CEESAT NOTES 59 drawback of the induction generator Reactive power consumption and poor voltage regulation under varying speed are the major drawback of the induction generators, but the development of static power converters has facilitated the control of induction generator, regarding output voltage and frequency.
CEESAT NOTES 60 Synchronous generator Synchronous generators are closely coupled devices and when they are used in wind turbines which is subjected to turbulence and requires additional damping devices such as flexible couplings in the drive train or to mount gearbox assembly on springs and dampers.
CEESAT NOTES 61 Towers Tower on which a wind turbine is mounted is not just a support structure. It also raises the wind turbine so that its blades safely clear the ground and so it can reach the stronger winds at higher elevations. Maximum tower height is optional in most cases, except where zoning restrictions apply. The decision of what height tower to use will be based on the cost of taller towers versus the value of the increase in energy production resulting from their use.
CEESAT NOTES 62 The tower must be strong enough to support the wind turbine and to sustain vibration, wind loading and the overall weather elements for the lifetime of the wind turbine. Tower costs will vary widely as a function of design and height.
CEESAT NOTES 63 Towers…. Studies have shown that the added cost of increasing tower height is often justified by the added power generated from the stronger winds. Larger wind turbines are usually mounted on towers ranging from 40 to 70 meters tall.
CEESAT NOTES 64 Environmental Aspects of Power Generation Using WECs Wind turbines are most environment friendly method of producing electricity. They do not pose any adverse effect on the global environment, unlike the conventional coal or oil-fired power plants. The pollution that can be saved per year from a typical 200 kW wind turbine, involving of substitution of 120 - 200 tonnes of coal which contain pollution contents as, Sulphur dioxide (SO2): 2 –3 tonnes, Nitrogen oxide (NOX): 1.2 to 2.4 tonnes, and other particulates of 150-300 kg. .
CEESAT NOTES 65 Audible noise The wind turbine is generally quiet. The wind turbine manufacturers generally supply the noise level data in dB versus the distance from the tower. A typical 600 kW wind turbine may produce 55 dB noise at 50 meter distance from the turbine and 40 dB at a 250 meter distance [4, 22] comparable with the noise level in motor car which may be approximately 75 dB. This noise is, however, is a steady state noise. The wind turbine makes loud noise while yawing under the changing wind direction. Local noise ordinance must be compiled with.
CEESAT NOTES 66 Research and development Research and development is going on to make wind power competitive with fossil fuel and nuclear power in strict sense, without taking into account of wind power’s social factors such as environment benefits.
CEESAT NOTES 67 Research and development Efforts are being made to reduce the cost of wind power by: design improvement, better manufacturing technology, finding new sites for wind systems, development of better control strategies (for output and power quality control), development of policy and instruments, human resource development, etc
CEESAT NOTES 68 About Enercon- E-30-230 kW- Gearless type--1 Variable speed drive, Continuous pitch regulation, Starts gen. at low speed of 2.5 m/s, Gearless construction, no transmission loss, Synchronous gen., draws < one % reactive power from grid, By using AC_DC_AC conversion, pumps the power at ‘grid frequency’,
CEESAT NOTES 69 About Enercon - E-30-230 kW- Gearless type--2 Produces power at all loads at near unity power factor without using capacitors Supply reactive power to the grid to improve grid power factor Slow speed generator of maximum 50 rpm Three independent air brakes, no mechanical brakes Lightning protection
CEESAT NOTES 70 Wind Turbine Design Wind turbine design is dictated by a combination of technology, prevailing wind regime, and economics. Wind turbine manufacturers optimize machines to deliver electricity at the lowest possible cost per kilowatthour (kWh) of energy.
CEESAT NOTES 71 Wind Turbine Design Design efforts benefit from knowledge of the wind speed distribution and wind energy content corresponding to the different speeds and the comparative costs of different systems to arrive at the optimal rotor/generator combination. Optimizing for the lowest overall cost considers design factors such as relative sizes of rotor, generator, and tower height.
CEESAT NOTES 72 Thanks to extensive R&D efforts during the past 30 years, wind energy conversion has become a reliable and competitive means for electric power generation. The life span of modern wind turbines is now 20-25 years, which is comparable to many other conventional power generation technologies. The average availability of commercial wind power plants is now around 98%. Thank You
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