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Windmills have been assisting mankind to convert the energy contained in wind to
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many other useful forms for the last two thousand years.
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Today's wind turbines are capable of converting a great amount of energy in
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the wind into electricity.
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This is due to the blades which are developed using state-of-the-art
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aerodynamic analysis and the other performance-enhancing equipment.
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In this video we will explore these different set of technology in a simple
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yet scientific way.
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First, let's get into its basic working
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If the blowing wind can turn the wing, we will receive electricity from the
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generator that is attached to it.
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However, how does the blowing wind turn the wing ?
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Let's have a close look at the blade.
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The Blade has a lot of airfoil cross-sections consisting of different
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sizes and shapes from the root to tip.
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The simple airfoil technology makes the wind turbine blade turn.
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That means that a lift force is produced when a fluid moves
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over an airfoil.
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This way the wind turbine achieves the basic rotation
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we are accustomed to seeing.
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Just as in a moving train
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you experience things relatively, the moving wind turbine blade also
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experiences the wind relatively.
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For the moving blade the relative wind velocity is
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as shown.
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Therefore the wind turbine blade is positioned in a tilted manner
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in order to align with the relative wind speed.
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As the blade velocity increases to the tip the relative wind speed becomes more
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inclined towards the tip.
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This means that a continuous twist is given to the blade from the root to tip.
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However this rotation cannot be directly coupled to a generator.
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Because the wind turbine blades typically turn at a very low rate of rpm
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due to the issues of the noise and mechanical strength.
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Considering this low-speed rotation we cannot produce
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any meaningful electricity frequency from a generator.
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So before connecting to the generator the speed is increased in a gearbox.
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The gearbox uses a planetary gear set arrangement
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to achieve the high speed ratio.
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A break also sits in the nacelle.
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The function of the brake is to arrest wind blade rotation
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during excessively windy conditions
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Consequently the electricity that is
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passed through the cables towards the base
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where a step-up transformer is situated.
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The wind turbine should face the wind
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normally for maximum power extraction.
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But the wind direction can change at any time.
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A velocity sensor
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on the top of the nacelle measures the wind speed and direction.
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The deviation in the wind's direction
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is sent to an electronic controller which in turn sends an appropriate signal to the
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yawing mechanism to correct the error.
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You can see how the yaw motors turn the nacelle.
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Thus the wind turbine will
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always be aligned with the wind direction:
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According to the wind speed the relative velocity anggle
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of the wind also changes.
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A blade tilting mechanism tilts the blades
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and guarantees a proper alignment of the blade with the relative velocity.
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Thus the blades are always at the optimum angle of attack
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with the relative wind flow.
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Efficiency of the wind turbine is the really interesting topic.
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To gain a good insight into wind turbine efficiency assume that you are measuring
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wind speed at upstream and downstream over wind turbine.
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You can note that the wind speed
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at the downstream is much smaller than the upstream.
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This is because the blades absorb
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some kinetic energy from the wind.
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The same amount of energy
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is converted as mechanical power of the wind turbine.
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It is interesting to note that
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a wind turbine absorbs 100 percent of the available kinetic energy
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only if the downstream wind speech becomes zero.
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However zero wind speed at downstream is a physically impossible condition.
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This cartoon animation clearly depicts this fact.
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Zero downstream speed simply means
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the whole flow is stock.
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This physical reality of the flow demands a certain amount of exit wind speed.
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That means that there is a theoretically maximum efficiency
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a wind turbine can achieve.
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This limit is known as Betz's limit.
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Essentially it means that no wind turbine in the world can
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ever cross the efficiency limit of 59.3 percent.
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We hope you have now developed a good inside of the operation a wind turbines.
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Thank You !
