How do Wind Turbines work ?
Windmills have been assisting mankind to convert the energy contained in wind to many other useful forms for the last two thousand years. Today’s wind turbines are capable of converting a great amount of energy in the wind energy into electricity.
This is due to the blades which are developed using state-of-the-art aerodynamic analysis and the other performance-enhancing equipment. In the article, we will define how to wind turbines work in scientific way.
Firstly, let’s get into its basic working
If the blowing wind can turn the wing, we will receive electricity from the generator that is attracted to it. However, how does the blowing wind turn the wing? You can look the picture
The blade has a lot of air foil cross-sections consisting of different sized and shapes from the root to tip. The simple air foil technology makes the wind turbine blade turn. Its mean that a lift force is produced when a fluid moves over an air foil.
This way the wind turbine achieves the basic rotation we are accustomed to seeing. Just as in a moving train, you experience things relatively, the moving wind turbine blade also experiences the wind relatively.
For the moving blade the relative wind velocity is as shown.
Therefore the wind turbines blade is positioned in a tilted manner in order to align with the relative wind speed. As the blade velocity increases to the tip the relative wind speed becomes more inclined towards the tip. The means that a continuous twist is given to the blade from the root to tip. However, the rotation can’t be directly coupled to a generator.
The wind turbine blades typically turn at a very low rate of rpm due to the issues of the noise and mechanical strength. Considering the low-speed rotation we can’t produce any meaningful electricity frequency from a generator. Therefore, before connecting to the generator the speed is increased in a gearbox.
The gearbox uses a planetary gear set arrangement to achieve the high speed ratio. Also, a break sits in the nacelle. The function of the brake is to arrest wind blade rotation during excessively windy conditions. Consequently the electricity that is passed through the cables towards the base where a step-up transformer is situated.
The wind turbine should face the wind normally for maximum power extraction
the wind direction change in any time. Therefore, a velocity sensor on the top of the nacelle measures the wind speed and direction. Also, the deviation in the wind’s direction is sent to an electronic controller which in turn sends an appropriate signal to the yawing mechanism to correct the error.
You can see how the yaw motors turn the nacelle. Therefore, the wind turbine will always be aligned with the wind direction. According to the wind speed, the relative velocity angle of the wind also changes. A blade tilting mechanism tilts the bladder and guarantees a proper alignment of the blade with the relative velocity. Therefore, the blades are always at the optimum angle of attack with the relative wind flow. Efficiency of the wind turbine is the really interesting topic. To gain a good insight into wind turbine efficiency assume that you are measuring wind speed at upstream and downstream over wind turbine.
You can note that the wind speed at the downstream is much smaller than the upstream. This is because the blades absorb some kinetic energy from the wind. The same amount of energy is converted as mechanical power of the wind turbine. Also, it is interesting to note a wind turbine absorbs 100 percent of the available kinetic energy only if the downstream wind speech becomes zero.