When I drove past a field of wind turbines on a recent road trip, I wondered how fast the blades can really spin before they are damaged. So, I did some reading to find out the maximum speed of wind turbines and what happens when that limit is exceeded.
Do wind turbines have a maximum speed? Every wind turbine is programmed internally to have a maximum speed depending on the size and design of the machine. When this speed is reached, the blades will be triggered to automatically stop using a variety of braking mechanisms.
Wind turbines are designed to protect themselves from weather conditions that are not ideal. Advanced technology inside machines take note of the wind speeds and react accordingly. However, it might not be possible for these mechanisms to protect the wind turbines in every situation.
Related: Does Wind Energy Produce Waste?
The Maximum Speed of Wind Turbines
The blades on a wind turbine spin according to the speed of the wind. If there is no wind, they will not react with movement at all. Once the turbine’s minimum speed is surpassed, it will use its internal features to detect the exact wind speeds and pass the message throughout the machine. Anemometers are commonly used for this purpose.
Once the wind speed information is collected, the rotor will spin the blades and they will continue to gain momentum off of the wind while taking its kinetic energy and passing it through the tower.
The maximum speed that is registered in every wind turbine is also known as the “cut-out speed” or “survival speed”. This value is calculated depending on the size and design of each individual turbine.
Smaller turbines that are more close the ground will generally have lower maximum speeds than larger ones that might be able to withstand stronger winds before any damage is done to the blades.
The average survival speed of any range of turbine size can be as low as 100-130 mph, going up to speeds of 180 mph for larger machines. This programming is necessary for every wind turbine to maximize safety and efficiency.
These limits are indicated by a power curve equation where the bottom of the curve shows the cut-in speed, or the minimum amount of wind power required in order to begin rotation, and the end of shows the maximum cut-out speed.
The area in between the minimum and maximum speeds indicates the rated speed the blades go through before hitting their peak limit. The power curve is not actually calculated, it is just created by matching the values of power in kilowatt hours to the speed the blades are rotating in meters per second and plotting them on the graph.
How Wind Turbines Stop Themselves From Spinning When They Reach Max Speeds
When the anemometer senses wind speeds that are higher than the cut-out speed, it sends a message to the wind turbine to automatically stop the blades from spinning.
During this process, the yaw drive will point the rotor in the direction where the wind is coming from in order to change the way the wind blows on the surface of the blades. This method is known as aerodynamic or pitch braking. There is a motor that is located in between both the blade and the rotor hub that connects the two pieces together.
The motor will spin the blades in a pattern that will make the wind slip through the gaps without adding any momentum to the rotation until they finally stop. Alternatively, the motor piece can be located on the tip of the blade instead of near the rotor hub in some wind turbine designs.
When pitch braking, the blades will spin out of the wind’s path from the motor in the same fashion until they are not spinning anymore.
In the event that the aerodynamic braking system does not work to stop the blades, the turbine will go through the process of mechanical breaking.
When the turbine brakes mechanically, the components inside of it will construct the rotor to manually stop it instead of allowing the rotation to slowly die out as it does during pitch braking. The mechanical brake looks like a round disk with several empty holes.
When the turbine needs to stop in case of an emergency, a stopper will be put through the holes to force the blades to stop rotating. This, however, is not the ideal way for the turbine to brake.
The rotor and blades are extremely heavy and the friction of the components can damage the inner parts of the turbine. This can cause unnecessary wear on the inside of the machine and shorten its life span if it happens too often.
Another alternative process to stop the blades of a wind turbine is called electrical braking. When this happens, the rotor will initiate a motion that rotates in the opposite direction to gently stop the blades from moving.
This motion will stop before it begins to cause the blades to rotate in the opposite direction, which could cause the components to scrape together and damage the machine as it does during a mechanical brake.
When weather conditions are too severe for wind turbines to properly function, they will automatically stop themselves from spinning as mentioned above. However, natural disasters like hurricanes and tornados have the potential to cause structural damage to the outer parts of the turbines.
Offshore turbines located near the ocean could end up with bent blades or just fall over completely after the storm settles. Currently, studies are being done in order to find ways to improve the construction of wind turbines so they can better withstand these kinds of harsh weather conditions.
Exploding Wind Turbines in Extreme Weather Conditions
In 2011, a video surfaced on the internet of a wind turbine in the UK exploding from the inside due to extremely fast winds. This happened due to a combination of brake failure and continuously strong gusts of wind that caused the turbine to lose control of itself.
The friction that occurs during braking methods in the event of high winds can cause the turbine parts to overheat internally. When turbines stop themselves from movement, they are supposed to turn the blades to face the direction of the wind and adjust rotation speeds to avoid gaining momentum from it.
However, internal overheating can cause loss of control for this function and the blades will not turn into the right direction.
When this happens, the generator begins to overheat and creates sparks of a fire inside of the turbine. If the turbine is not able to stop itself aerodynamically, the emergency mechanical brake will kick in, forcefully stopping the movement by holding the blades in one place.
While the mechanical breaking process is creating resistance against the blades, there is still extreme heat forming inside of the turbine. The continuous wind speeds will continue to move the blades against the force of the braking mechanism, causing the entire thing to explode from the inside.
In conclusion, all wind turbines have set maximum speed thresholds as well as special braking functions that come into play to enforce these limits. While it is true that each turbine comes with these protective features, they can not always prevent damage in the event of severe weather conditions.
Are Wind Turbines Supposed to Spin Fast all the Time?
Although turbines have the capability of reaching very high rotation speeds, it is actually better for them to move a little slower. Stability is prioritized over speed because frequently fast momentum can damage the working parts and shorten the life span of each turbine overall.
Newer turbines are currently being designed to reach lower maximum speeds. This way, they will be able to reach their maximum speed more easily and more often without causing damage to the machine. This will also allow them to generate as much power as they possibly can, generously boosting power efficiency.
How Much Energy Can Turbines Actually Take From the Wind?
We know that the blades of a wind turbine can reach almost 200 mph as a maximum speed, but the actual amount of kinetic energy the blades are able to collect from the wind is an entirely different statistic.
There is something that applies to wind turbines called the Betz Limit, which is a theory about the power levels that a wind turbine is capable of receiving from the wind. It suggests that turbines can only capture exactly 59.3% of the wind’s kinetic energy at any given time, no matter how fast the blades are spinning.
The actual amount of energy each turbine can extract will depend on its size and a few other factors. Large, utility-scale turbines can reach up to 80 percent of this limit as a maximum.
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.