How it works
A wind turbine has many components that work together to transfer the kinetic energy of the wind to mechanical energy of rotating propellors and finally to the desired electrical energy that can be distributed and used in the National Grid.
Wind:
Wind is the movement of air from a high-pressure to a low-pressure area, a larger atmospheric pressure gradient causes higher wind speeds. It is caused because the Sun unevenly heats the surface of the Earth, the hotter air rises, and cooler air moves in to fill the space, this is wind. [1]
Not all of the wind power can be utilised by a wind turbine, in fact the maximum power that can be produced from wind power, was discovered by Betz in 1926. The equation is as follows:
***equation***
Where PBetz is the maximum power extracted from the wind, r is the air density, A is the area of the wind turbine rotor, V is the wind velocity, and CP Betz is a constant of 0.59. This equation shows increasing wind speed by 10% causes a 30% increase in the available power from a wind turbine. [2]
Propeller Blades:
These are the most visible part of the wind turbine, they rotate as the wind blows and cause a rotor to spin which in turn causes the generator to produce electricity. [3]
Gear Box:
The generator needs speeds of around 1500 revolutions per minute (rpm) and generally the wind only provides about 15-20 rpm, therefore a gear box is needed. This increases rotational speeds up to 1000-1800 rpm which is needed for the induction generator to produce electricity. [3]
Generator:
Electromagnetic Induction-
Generators are based on the concept of electromagnetic induction, which says that a voltage is produced when a conductor is moved through a magnetic field, as it intersects the magnetic field lines causing a change in flux. If the conductor is connected in a circuit, then current flows. The voltage produced is called the electromotive force (emf), and can be calculated from the following equation:
***equation***
Where e is the emf, N is the number of turns of coil on the conductor, and df/dt is the rate of change of magnetic flux. The minus sign is because the emf is in such a direction to oppose the change in flux.
Electromagnetic induction can also work in reverse so if an electrical charge is moving, then a magnetic field is generated. [4]
Induction Generator-
The most common generator used in wind turbines is an induction generator as it works for variable wind speeds. This only works when the wind turns the rotor at a speed above the synchronous speed, which is typically around 1000-1800 revolutions per minute. [3]
It requires an input of power as alternating current is supplied to coils on the stator, the stationary part of the generator. This creates a changing magnetic field. Coils on the rotor are moving and intersect the stator magnetic field lines, inducing a current in the coils by electromagnetic induction. This rotor current in turn creates a magnetic field which then is intersected by the stator coils. Therefore, an active current is induced in these stator coils, this current is the electrical output of the generator. [5]
Transformer:
This is at the base of the mast, it steps the electricity produced up to the voltage of the network, so it can be transported on the national grid and used.
These are essentially made up of 2 coils wrapped around a core and again use the idea of electromagnetic induction. AC current flows
through the primary coil which produces a changing magnetic field, this then induces a e.m.f. in the secondary coil as the magnetic field is changing so there is a change in flux, which then causes a current to flow.
Transformers can vary voltage due to the number of turns of each coil, so to step up the voltage from that produced by the wind turbine to that used in the national grid, a transformed with more turns on the secondary coil than on the primary coil is needed. The following equation is used to calculate the required number of turns on each coil:
***equation***
Where Vp is the voltage produced from the wind turbine, Vs is the voltage used in the national grid, Np is the number of turns on the primary coil and Ns is the number of turns on the secondary coil. [6]
Substation:
The electricity from all wind turbines pass through the substation and then it is fed into the national grid. [7]
References:
[3] https://energy.gov/eere/wind/inside-wind-turbine-0
[4] http://www.egr.msu.edu/classes/ece480/capstone/fall15/group10/subpage/application%20note%20ari.pdf
[5] https://www.windpowerengineering.com/generators/generators/
[6] http://www.tubebooks.org/Books/Lee_1955_Electronic_Transformers_and_Circuits.pdf
[7] https://energy.gov/eere/wind/animation-how-wind-turbine-works