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Why Do Some Wind Turbines Stop Turning?

Why Do Some Wind Turbines Stop Turning?

When I drove past a wind turbine recently, I noticed that the blades weren’t spinning at all. So, I did some research to find out why wind turbines stop turning. 

Why do some wind turbines stop turning? Wind turbines can stop turning their blades due to a variety of factors including wind speeds that are too fast or too slow and extreme weather conditions. The turbines will stop themselves from spinning if they cannot get any energy from the wind or if their blades will be damaged by a movement that is too rapid. 

It can be confusing to see a wind turbine in real life with its blades standing still because they are supposed to spin to collect energy from the wind. However, there are some circumstances throughout their lifetimes in which wind turbines will stop turning their blades for one reason or another. 

Related: Just Three Blades? Why Most Wind Turbines Use Three Blades

The Turning Functions of a Wind Turbine

Wind turbines are made up of multiple intricate components that work together to spin the blades and collect the wind’s energy. The component that is first in line in this process is called the anemometer. The anemometer is a small rotating piece that sits on top of the turbine and looks similar to helicopter blades.

Its function is to gauge the wind’s speed and transmit it through the turbine to signal the rest of the components whether it is time to start spinning the blades or not.

The controller is an inner component that receives signals from the anemometer and starts the turbine’s functions from the inside. Located within the nacelle, this piece is also the one that will stop the turbine’s blades from turning if necessary.

The nacelle is one of the largest components on the turbine with other parts inside of it. For some utility-scale turbines, the nacelle is long enough to fit an airplane on top of it.  It is located on top of the tower behind the blades and encompasses the controller, gearbox, speed shafts, generator, and the brake.

The generator produces electricity within the turbine when the wind’s energy is passed through the machine. Connected by the gearbox, the high-speed shaft is what pushes turning speeds through the generator and the low-speed shaft pushes more controlled speeds out toward the blades.

The gearbox itself is the component of the turbine that multiplies the energy that is taken in by the turbine. 

It does this by multiplying the rate of rotations per minute, usually tripling it, in order to effectively generate usable electricity that has enough power. Finally, the brake piece that is also located within the nacelle will stop the blades from moving if the other components send the signal that it is necessary.

There are a few different ways that the brake function is able to stop the blades from turning, which I will get to in the upcoming sections. 

The spinning section of the wind turbine is collectively known as the rotor, which is the blades and the rotor hub together. The rotor hub is essentially the centerpiece that is in between the fan of blades.

It gains momentum from the inner components of the turbine when it is time to spin and passes it along through the blades. There is an additional component related to the blades called the pitch, which keeps the blades out of the direct wind to keep a steady turning pace and also helps to stop them when the wind speeds are not ideal for producing electricity. 

All of these components are held up by the tower, which is a slender cylinder shape that is usually made of some type of steel material. It is ideal for this piece to extend as high into the air as possible in order to be able to collect the most wind energy.

The entire tower and all other working parts are held in place by the foundation, which is commonly filled into the ground with concrete, although it can be made out of steel as well in certain locations that permit it. 

For example, a wind turbine in a field will probably have a concrete foundation, while an offshore turbine in the ocean will most likely stand on a steel base that emerges from the water.

These last two components are vital to the functions of the wind turbine because they serve the purpose of keeping it standing still as well as allowing it to be able to withstand strong wind speeds without toppling over. 

So now that the parts of a wind turbine are understood, what happens inside of the turbine when the blades start to spin? As mentioned before, the entire process of extracting wind energy begins with the tiny anemometer piece that sits on top of the nacelle.

When the wind begins to blow, the anemometer will spin according to the force that the wind is exerting on it and send a message through to the inside of the turbine. The signal will be received by the controller inside of the nacelle and the turning action will commence. Depending on the direction of the wind, the pitch system will rotate the blades to keep them safe from any damage and in order to get the most energy possible. 

When the blades receive the signal that the current wind speed is ideal, it will begin to turn freely according to the speed of the wind.

The force that is exerted on the blades is known as lift, where the wind speeds past the blades and they react by turning around the axis of the tower. The faster the wind blows, the faster the turbine’s blades will spin. 

When the wind is blowing, it is producing something called kinetic energy, which is created by movement. This kinetic energy will enter the inside of the turbine through the rotor hub in the middle of the blades as they are spinning according to the pace that the wind is blowing.

When the energy is received by the generator, it will be spun around multiple loops of copper wire to be multiplied and transformed into mechanical energy. 

Mechanical energy is created when the wind’s kinetic energy is added to the potential energy from within the turbine. During the process of creating mechanical energy, electrons will be given off in order to turn it into electricity.

The electrons travel through another component called the step-up transformer that increases the capacity of the electricity it was given by almost five times more. 

Once the electricity has been fully converted after passing through each one of the turbine’s inner parts, it will travel down the tower’s shaft and be transported to an electrical substation to be distributed from there. 

The Factors that Influence When a Wind Turbine Spins 

There are certain factors that influence when a wind turbine will spin its blades and when it will stand still instead. All of these factors, however, are dependent on the speed of the wind at the given time.

Turbines have advanced technology that is programmed within them to detect when the blades will be able to consume enough energy from the wind.

These speeds are determined by thresholds that are built into the machine at the installation called cut-in and cut-out speeds, or in other words, the minimum and maximum turning speeds. 

The cut-in speed is the absolute minimum amount of wind power that is required for the turbine’s blades to be able to spin. Without this minimum speed, it will be impossible for the blades to notice the presence of some kind of friction against them and begin to turn the opposite way.

The average cut-in speed for a regular wind turbine lands around 3 to 4 meters per second or up to 8 miles per hour. In the absence of sufficient energy being created by the wind, the anemometer function will not detect enough pressure to pass the message along the machine through the nacelle in order to start up the blades’ turning function.

The minimum speed of 8 miles per hour is essential for the turbine to gain any kind of energy off of the wind’s momentum.

The cut-out speed, on the other hand, is the absolute highest speed that the turbine can handle before there is any damage done to its moving parts. This function will be used when the wind speeds are extremely high in the event of a severe storm or natural disaster that could attack the blades.

The typical cut-out speed for a wind turbine on the smaller end could be programmed to anywhere from 60 to 100 miles per hour, whereas a larger utility-grade turbine might be able to withstand speeds up to 180 miles per hour before shutting down completely. 

Both the cut-in and cut-out speed are beneficial features to the wind turbine because they help protect the hardware as well as achieve as much energy efficiency as possible. 

In the absence of a minimum speed requirement, the wind turbine might be spinning its blades constantly without any kind of control. This would be a significant waste of energy because the cut-in speed corresponds with the minimum wind speed to where sufficient electricity can even be generated. 

Without a maximum speed threshold in place, the turbine’s blades would constantly be spinning out of control and would eventually get damaged or break altogether. In the event of extreme weather conditions, the cut-out speed helps to keep the machine in-tact as much as possible until it is permitted to resume functions. 

Both of these important functions prevent premature damage and wear and tear to the wind turbines, helping them to reach as close to their full life expectancy as possible. 

How Wind Turbines Stop Themselves From Spinning

When either end of the minimum and maximum speed thresholds of a wind turbine are detected, the braking function within the nacelle comes into play to stop the blades from spinning. There are a few different methods of braking that the turbine might use in certain situations that require them. 

The first type of braking function is called aerodynamic braking, or pitch braking. This is the most practical form of braking for a wind turbine, and will usually be executed first if the blades need to stop for any reason. The process of pitch braking begins when the controller is notified by the anemometer that the wind speeds are not ideal for blade rotation.

The pitch control function will then rotate the blades into the opposite direction of the current wind. This action will force the wind to brush against a different area of the blades that will not create any more lift or momentum to the rotor piece. 

The wind will eventually begin to slip through the gaps in between each blade as the turbine gets a strategic speed under control. This function is also carried out by the motor that is located somewhere near the blades, either toward the hub or outward inside the tip of one of the blades.

This pattern of rotation will continue until the blades are completely out of the wind’s path and the rotor slowly and naturally comes to a complete stop

In the event that the wind speeds are just too strong and the aerodynamic braking function is not working to stop the blades, a process called mechanical braking will be tagged into the race. 

Mechanical braking is almost like an emergency brake for wind turbines. When the blades should no longer be spinning, the internal components will grind together to manually stop them instead of allowing the rotation to slowly die out as it does during pitch braking. 

The mechanical brake itself looks like a round metal disk with several empty holes around its edges. This function is carried out when an emergency stopper piece is pushed through one of the holes to force the blades to stop rotating. 

Mechanical braking is not the best option for stopping the rotor blades, because it can cause unnecessary friction against the moving parts and put additional wear and tear on the machine.

There is the risk of certain components needing replacement due to the extremely heavy friction that they endured, which can become expensive. If this function is used too often, the wind turbine might not be able to last through its entire 20-year lifespan. 

The third and final braking process for wind turbines is called electrical braking. This function is installed in some turbines and is similar to the braking system of a car.

When electrical braking is used, the rotor will send a motion through the machine that causes the blades to rotate in the opposite direction. Eventually, the rotor blades will overpower the adverse wind speeds and come to a complete stop.

The electrical braking process, when working properly, should stop the blades from spinning in this direction before the parts begin to scrape against each other. 

How Often Wind Turbines Turn Their Blades

Wind turbines will not be spinning their blades and producing energy non-stop throughout their entire life for a few different reasons. First of all, the earth’s wind patterns are very scattered and unpredictable.

There is no way to know exactly how much wind there will be every day for the rest of the wind turbine’s lifetime. Even if so, it would be impossible to expect the wind to blow at sufficient speeds all year long in the area of each wind turbine. 

With that being said, statistics show that the average wind turbine will be able to effectively create energy up to 85 percent of the time. There are also additional factors that determine how much wind energy each turbine will realistically be able to produce during their lifetime, no matter how often or fast their blades are spinning.

There is a theory called the Betz Limit, which concludes that the maximum energy efficiency of a wind turbine will be no more than 59.3 percent. In other words, it is only possible for one wind turbine to extract 59.3 percent of the wind’s kinetic energy at any given time regardless of turning speeds. 

As you can see, there are a few common circumstances that will cause a wind turbine to stop turning its blades, all of which are directly related to the wind speeds that it depends on. However, the frequency of these circumstances will depend on the size and location of each individual turbine. 

Related Questions

What Can Happen to a Wind Turbine if it Doesn’t Effectively Stop Itself From Turning?

Years ago in 2014, there was a video that surfaced on the internet of a UK wind turbine exploding in extreme weather conditions. This happened due to the combination of brake failure and very high wind speeds, however, this will not frequently occur among the average everyday wind turbine. 

Is There a Way To Boost Wind Turbine Efficiency?

Although there are limits to how much wind energy each turbine can effectively extract from the wind, certain preventative measures can be taken to ensure maximum efficiency. If there are too many turbines in one area, it is possible for them to take most of the momentum from the wind before it gets to the next one. To avoid this, it is always best to keep a minimum distance between each turbine. 

Learn More

If you’re serious about learning more about wind energy, I recommend the Wind Energy Handbook on Amazon. This book is great for both students and professionals, and it holds invaluable information on the subject of wind power.