When I started researching this blog, I sought to find topics related to the electrical engineering of a wind tower. As a column for analog engineers, I was particularly interested in what the electronics were that produced the AC voltage for the grid even though I had learned most of them in an earlier study. As it turns out, I uncovered far more than I could fit into a single blog. Instead of stringing the subject out over several blogs, I decided to summarize the material that I found by relating it to the subjects listed in the bullets below.
- Wind turbine function (hey, I’m a physics major so vector analysis intrigues me)
- Wind turbine components (the electronics and gearing)
- Wind turbine maintenance (a great human interest story)
Wind turbine function
“How do Wind Turbines work ?” offers one of the best overall explanations of the wind tower parts and their function.
There are several control systems at work in a wind mill including the ability to face the turbine into the wind (yawing) and the control of the blade angles (pitch). Both of these require motors and motor control. In addition to this video, yawing and pitch are explained well in “Wind turbine design”. The interesting part is that a wind tower yawing can actually cause the cables inside to twist up like tethered dogs commonly do. However there is intelligence built into the wind tower so that it in effect “unwinds” the cables. Perhaps there’s a patent in there somewhere that will appeal to dog owners.
This work also uses physics and vectors that explain how the wind actually propels the blades. There is a speed analysis that shows the maximum efficiency of a wind tower is 59% (Betz’s limit) again using the laws of physics.
Wind turbine components
The main components of a wind turbine are the blades that turn the shaft that spins a generator in order to make electricity. Most of the videos talk about these parts. “What’s inside a wind turbine?” goes a little further and explains the location of many of the parts. There is a really good explanation of the power electronics on this Wikipedia page. Most designs use electronic control to generate the 60 Hz sine wave although time 6:33 in this article briefly addresses a direct drive wind tower.
This double-fed induction generator video shows how a doubly fed generator is employed to create three phase power. As shown in the figure, this requires a DC link and capacitors. Capacitors are no stranger to failure in power electronics so it’s no wonder that workers have to monitor the systems. Other than that, the control is similar to bidirectional motor controllers using IGBTs and rectifier diodes in a full bridge arrangement. Because the power is megawatts and the initial voltage generation is around 690 volts, these have to be some rather large components. In order to step up the voltage from the generator, transformers are used. There is also protection built in as the speed of the wind mill gets multiplied by the winding ratio as do the spikes on the grid power line.
Without going into a lot of detail, the majority of the references provide explanations of how rotating speed gets to a 60 Hz sine wave. Obviously the converters are phased for this purpose however if you’re like me you often time the blades as they go around. I always thought they spun at one turn per minute but then again, I’m over 50 so perhaps I’m not correctly recalling what I measured. I learned that “typical rotation speeds for wind generators are 5–20 rpm while a directly connected machine will have an electrical speed between 750 and 3600 rpm”. This is turned into a higher speed by a gear box which in turn determines the generator angular speed.
The best explanation of the physical components and approximate dimensions is the video above entitled “What’s inside a wind turbine”. One note is that a combination of blades and proper pitch are used to stop rotation and pins are inserted into the shaft to lock the blades from spinning. This is crucial for maintenance.
Wind turbine maintenance
Wind turbine maintenance involves the blades which in turn involves dangling from ropes hundreds of feet in the air. This video documents a wind tower worker’s interview about her job. What really caught my eye was her story about how she was disabled early in life which kept her inside watching as the other children played outside. She breaks down when talking about this sensitive part of her life. I actually have a gas powered monster truck that I want to electrify so that I can bring it inside of hospitals and activate for children facing similar restrictions. What a life that would be traveling the country and visiting sick children while blogging about electronics. I hope someday to share the design on Planet Analog. I think the design would interest readers as would the ability to apply our skills to coveted projects that enhance those less fortunate.
Getting back to our maintenance subject, note the hazards addressed in the video above including getting struck by lightning a well as out running forest fires. Perhaps now your job won’t appear to be as much as a hassle after all once you see the risky job of a maintenance worker. It’s very interesting in addition to being heart wrenching. Like any job where safety is a factor, wind speed can limit when to perform maintenance. Based on the enclosed photo, this is a good idea.
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