Learn Wind electric conversion system
Transcript of Learn Wind electric conversion system
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WIND
ELECTRIC CONVERSION
Basic Questions for Wind System DesignWind Energy Potential in India
Monitor speed, direction and temperature
Wind resource Evaluation
Components of WECS, their FunctionsOperating characteristic speeds
Gear for turbine to generator speed
conversion
Energy Flow and Control in WECS
Generators
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Basic questions for
Wind System Installation
Is there enough wind ?
Are tall wind towers allowed in your area?
Do you have enough space?
How much electricity do you need or wantto produce?
Do you want to connect to the utility grid
or be grid-independent? Can you afford a wind energy system?
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Kinetic > Mechanical > Electric
Wind is created by the unequalheating of the Earths surface by
the sun. Wind turbines convert
the kinetic energy in wind intomechanical power that runs a
generator to produce clean
electricity.
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Wind resources evaluation
Apart from having a good wind turbine, the most
critical aspects for the success of investment in the
wind energy sector are (i) having a good site and
(ii) an accurate assessment of the wind resource at
the site over the season of active wind.
Wind Resource Monitoring consists of following
activities (i) Siting, (ii) Wind Monitoring
(iii) Wind Resource Mapping
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For wind data from selected stations,
essential attributes are:
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Non-grid power for Pumping Water
One- to 10-kW turbines can be used inapplications 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.
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Turbine Component Function
Nacelle
Contains the key components of the wind turbine,
including the gearbox, yaw system, and electrical
generator.
Rotor bladesCaptures the wind and transfers its power to the rotor
hub.
HubAttaches the rotor to the low-speed shaft of the wind
turbine.
Low speed shaft Connects the rotor hub to the gearbox.
Gear box
Connects to the low-speed shaft and turns the high-
speed shaft at a ratio several times (approximately 50
for a 600 kW turbine) faster than the low-speed shaft.
High-speed shaft
with mechanical
brake
Drives the electrical generator by rotating at
approximately 1,500 revolutions per minute (RPM).
The mechanical brake is used as backup to the
aerodynamic brake, or when the turbine is beingserviced.
Electric generator
Usually an induction generator or asynchronous
generator with a maximum electric power of 500 to
1,500 kilowatts (kW) on a modern wind turbine.
Yaw mechanism Turns the nacelle with the rotor into the wind usingelectrical or other motors.
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Electronic controller
Continuously monitors the condition of the wind
turbine. Controls pitch and yaw mechanisms. In
case of any malfunction (e.g., overheating of the
gearbox or the generator), it automatically stops
the wind turbine and may also be designed to
signal the turbine operator's computer via a modem
link.
Hydraulic systemResets the aerodynamic brakes of the wind turbine.
May also perform other functions.
Cooling system
Cools the electrical generator using an electric fan
or liquid cooling system. In addition, the systemmay contain an oil cooling unit used to cool the oil
in the gearbox.
Tower
Carries the nacelle and the rotor. Generally, it is
advantageous to have a high tower, as wind
speeds increase farther away from the ground.
Anemometer and wind
vane
Measures the speed and the direction of the wind
while sending signals to the controller to start or
stop the turbine.
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Some definitions: Solidity: In reference to a wind energy
conversion device, the ratio of rotor bladesurface area to the frontal, swept area that therotor passes through.
wind rose: A diagram that indicates the averagepercentage of time that the wind blows fromdifferent directions, on a monthly or annualbasis.
power curve: A plot of a wind energy conversiondevice's power output versus wind speed.
power coefficient: The ratio of power produced
by a wind energy conversion device to the powerin a reference area of the free wind stream.
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WIND
Wind Speed at 10 m height
SPEED
Beaufort scale
SCALE
Wind
0.0-0.4 m/s (0.0-0.9 knots) 0 Calm
0.4-1.8 m/s (0.9-3.5 knots) 1 Light
1.8-3.6 m/s (3.5-7.0 knots) 2 Light
3.6-5.8 m/s (7-11 knots) 3 Light
5.8-8.5 m/s (11-17 knots) 4 Moderate
8.5-11 m/s (17-22 knots) 5 Fresh
11-14 m/s (22-28 knots) 6 Strong
14-17 m/s (28-34 knots) 7 Strong
17-21 m/s (34-41 knots) 8 Gale
21-25 m/s (41-48 knots) 9 Gale
25-29 m/s (48-56 knots) 10 Strong Gale
29-34 m/s (56-65 knots) 11
>34 m/s (>65 knots) 12 Hurricane
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Requirements: wind to electric Conversion
Force of wind needs turbine area, height
and direction control:
turn turbine and generator shaft,
produce electricity
wind resources at 50meter height Wind translational > rotational > electric
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How Do Wind Turbines Work?
Todays turbines are versatilemodular sources of electricity.
Their blades are aerodynamically
designed to capture the maximum
energy from the wind. The wind turns
the blades, which spin a shaftconnected to a generator
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The formula for calculating the
power from a wind turbine is:
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Turbines today are horizontal axis upwind
machines with two or three blades, made of
a composite material like fiberglass.
The amount of power a turbine will produce
depends on the diameter. The diameter of
the rotor defines its swept area, or the
quantity of wind intercepted by the turbine.
The turbines frame is the structure onto
which the rotor, generator, and tail are
attached. The tail keeps the turbine facing
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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
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number of blades
The number of rotor blades and the total area theycover 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 shouldbe 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 windturbines have only two or three blades on their rotors
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Operating Characteristics
All wind machines share certain operatingcharacteristics, such as cut-in, rated and cut-outwind speeds.
Cut-in Speed
Cut-in speed is the minimum wind speed at which the windturbine will generate usable power. This wind speed istypically between 7 and 10 mph.
Rated SpeedThe rated speed is the minimum wind speed at which the
wind turbine will generate its designated rated power. Forexample, a "10 kilowatt" wind turbine may not generate 10kilowatts until wind speeds reach 25 mph. Rated speed for
most machines is in the range of 25 to 35 mph.
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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.
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Generators
The generator is what converts the turning
motion of a wind turbine's blades intoelectricity.
Inside this component, coils of wire are rotated
in a magnetic field to produce electricity.
Different generator designs produce eitheralternating current (AC) or direct current (DC),
and they are available in a large range of
output power ratings.
The generator's rating, or size, is dependent onthe length of the wind turbine's blades because
more energy is captured by longer blades. 29
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It is important to select the right type of
generator to match your intended use. Most
home and office appliances operate on 120
volt (or 240 volt), 60 / 50 cycle AC. Some
appliances can operate on either AC or DC,such as light bulbs and resistance heaters, and
many others can be adapted to run on DC.
Storage systems using batteries store DC and
usually are configured at voltages of between
12 volts and 120 volts.
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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.
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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 speedsnecessary for efficient electricity production.
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Towers: Tall structures
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. 33
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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.
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