Score
Title
98
AskScience Panel of Scientists XVIII
550
AskScience AMA Series: I am Melinda Krahenbuhl and I am the director of the Reed Research Reactor, the only nuclear reactor operated primarily by undergraduate students. AMA!
8468
What elements are at genuine risk of running out and what are the implications of them running out?
269
Can you break sound barrier under water or any other material?
4021
What’s the largest star system in number of planets?
19
Why does plastic turn white at the creases when folded/bent?
3
How does thermal imaging work?
21
Do microwaves leave residual changes to molecules after heating?
4
Can a setup of hall engines provide enough thrust to keep a satellite stationary above earth?
2
Does the temperature have any (noticable) effect on air resistance?
6
How does a memristor work?
1
How does radiation poisoning work?
1
How is the height of the mountain measured?
3827
What is the effect, positive or negative, of receiving multiple immunizations at the same time; such as when the military goes through "shot lines" to receive all deployment related vaccines?
4
If a planet had a radius that was equal to the altitude of Earth’s geosynchronous orbit, but had the same mass and rotational period as the Earth now, would there be reduced or zero gravity on the surface?
1
What is lost and what is preserved in a particle collider?
8
Why does snow melt in the sunlight, even when the temperature outside is below freezing?
11
Mar's summer temperature can be 20 celsius. Could a human survive with just an oxygen mask?
2
Is there an altitude at which there is no longer a speed of sound?
0
How would a moving target affect the rate of nuclear fission vs a stationary target?
14
What would a spaceship moving at 0.9c firing lasers both in front of it and behind it look like to an external reference frame?
6
Does adiabatic warming occur when air descends in the Earth's polar cells?
24
How does the cosmic microwave background persist? Why hasn't it been distorted and destroyed by new sources of energy pumping into space?
6
How does cancer metastasis work?
7
Can a comet maintain an atmosphere?
1
How does RFID blocking material work?
0
Does the Meissner effect relate to Lenzs law?
9
Why hasn't The Asteroid Belt formed a planet?
10
Can you use a normal (CMOS) camera for detecting scintillation?
3
How do people know that the Island of Stability exists? And could there possibly be another "island" after it?
59
How can brain cells cause tumours even though they can not multiply?
7
How far back can you go before carbon dating becomes unreliable?
2
How does a computer process “simple” events?
1578
Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology
3
What is the nonrenewable fuel cost to produce x quantity of electricity?
1132
What triggers beta particles to form, and for what reason can they not penetrate substantially thick aluminium?
0
What is the strongest a magnet could be?
1242
If capacitance increases as distance between plates decreases, why aren't there very small 1F capacitors?
0
What makes astronomers think life in general isn't possible on gas giants?
1
How applicable are Newtonian Physics in real life? Is it completely false or are there some concepts which can be used to accurately predict real-life situations?
1050
is it possible to move an object in circular motion using magnets?
4
What would hydrogen in metal form look like?
208 NLJeroen It will probably use profile wire with dozens of turns. But that depends on the voltage. 2 MW at 400V will be in the kA, a bit much, so it will probably be 6 or 10 kV. [Here](https://www.youtube.com/watch?v=5P6YVi2mB6Q) is a video of someone repairing a standard 400V generator. Each bundle is one coil, which will be put in series depending on the voltage configuration. We rewind low voltage generators at work, I might be able to ask there tomorrow. *Video is not my work, but some competitor.* *Edit: I checked, we haven't repaired a wind turbine generator for years. We only certificate (test) and store them.*
82 scornucopia This is actually a very difficult question to answer. A 2MW wind turbine in the US (60Hz) will _probably_ have a 690V 3-phase 6-pole doubly-fed induction generator with a synchronous speed of 1200 RPM (note: the generator assembly, including electronics, is _not_ synchronous overall, but the machine itself has a synchronous speed of 1200 RPM; see Edit 2, below). This means that it will have at least 3 armature windings (one per phase) and 3 field windings (one per pole pair). So there are at least 6 copper coils, not just 1. Part of the reason why it's hard to say how many turns there are is because, even within the assumptions above, there are a plethora of different generator designs that will, more-or-less, achieve the same result. For example, the number of slots in the armature could change the number of turns by a factor of 2. Put more turns on the field windings, or more current through it, and you need fewer armature windings. Change the way the windings are wound (lap winding, wave winding, ...) and the number changes again. The upshot is that nobody in the wind industry or academia thinks of "number of turns" as being an important characteristic of the generator. This is the domain of a handful of generator design specialists in companies like GE and Siemens who actually make the generators themselves. So, I think you're unlikely to get a good answer to this question. In general, the output voltage from the armature windings is a function of the magnetic flux (due to the field windings) and the number of turns. The magnetic flux, in turn, is a function of the field current and number of turns. As a rule, you would expect "many" field windings and relatively few armature windings for a low-voltage machine such as this. If I had to make a semi-informed guess, I would think that the most likely number of turns on each of the 3 armature windings would be "dozens" (based on a one or two layers of a handful of turns in each of 12 or 24 armature slots), while the most likely number of turns for the field windings would be "hundreds" (300? 800? I have no idea). Edit: in the US (60Hz), the generator is probably 6-pole, rather than 4 (as originally posted). 4-pole generators in wind-turbines are more common in 50Hz countries, e.g. the venerable Vestas V-90 1.8/2.0 MW turbine uses a 4-pole generator for 50Hz and a 6-pole for 60Hz. Edit 2: There was a bit of confusion here (comments below). AC machines are just arrangements of iron and copper. The mechanical rotation of the shaft bears a fixed relationship to the frequency of the AC output (for a generator) or input (for a motor). In wind turbine DFIGs, clever electronics provide the illusion of asynchronous operation, but the machines themselves are unchanged and have "a synchronous frequency" despite being used in asynchronous service.
166 [deleted] [removed]
18 -NICX From experience on Enercon wind turbines, they run a direct drive synchronous generator. This generator, when operating at full output, is typically only turning about 17 rpm, and produces 400 volts, 3 phase power. The generator is wound manually in the factory and I believe each coil is 58 turns, and then 2 parallel coils per slot, (4 coils essentially), for the 2 MW machine.
26 leahcim165 Ok, what is happening in this thread? Why don't wind turbine enthusiasts understand how to answer a question? Instead, it's endless "oh, it depends on such and such variables" - duh! Everything does. We're asking what the TYPICAL NUMBER OF TURNS is. If someone asked, "how many transistors are there in a typical 2017 cpu" (it's about 1 billion), the people in this thread would endlessly say "it's impossible to determine" rather than actually using their knowledge to help inform.
3 mjss518 I think offering a calculated approximation can be done using the link provided...19rpm at 660V nominal output, and perhaps a built in transformer. http://img.directindustry.com/pdf/repository_di/51394/pdf-document-2mw-permanent-magnet-synchronous-gearless-wind-turbine-generator-110785_1b.jpg
207 0 NLJeroen It will probably use profile wire with dozens of turns. But that depends on the voltage. 2 MW at 400V will be in the kA, a bit much, so it will probably be 6 or 10 kV. [Here](https://www.youtube.com/watch?v=5P6YVi2mB6Q) is a video of someone repairing a standard 400V generator. Each bundle is one coil, which will be put in series depending on the voltage configuration. We rewind low voltage generators at work, I might be able to ask there tomorrow. *Video is not my work, but some competitor.* *Edit: I checked, we haven't repaired a wind turbine generator for years. We only certificate (test) and store them.*
86 0 scornucopia This is actually a very difficult question to answer. A 2MW wind turbine in the US (60Hz) will _probably_ have a 690V 3-phase 6-pole doubly-fed induction generator with a synchronous speed of 1200 RPM (note: the generator assembly, including electronics, is _not_ synchronous overall, but the machine itself has a synchronous speed of 1200 RPM; see Edit 2, below). This means that it will have at least 3 armature windings (one per phase) and 3 field windings (one per pole pair). So there are at least 6 copper coils, not just 1. Part of the reason why it's hard to say how many turns there are is because, even within the assumptions above, there are a plethora of different generator designs that will, more-or-less, achieve the same result. For example, the number of slots in the armature could change the number of turns by a factor of 2. Put more turns on the field windings, or more current through it, and you need fewer armature windings. Change the way the windings are wound (lap winding, wave winding, ...) and the number changes again. The upshot is that nobody in the wind industry or academia thinks of "number of turns" as being an important characteristic of the generator. This is the domain of a handful of generator design specialists in companies like GE and Siemens who actually make the generators themselves. So, I think you're unlikely to get a good answer to this question. In general, the output voltage from the armature windings is a function of the magnetic flux (due to the field windings) and the number of turns. The magnetic flux, in turn, is a function of the field current and number of turns. As a rule, you would expect "many" field windings and relatively few armature windings for a low-voltage machine such as this. If I had to make a semi-informed guess, I would think that the most likely number of turns on each of the 3 armature windings would be "dozens" (based on a one or two layers of a handful of turns in each of 12 or 24 armature slots), while the most likely number of turns for the field windings would be "hundreds" (300? 800? I have no idea). Edit: in the US (60Hz), the generator is probably 6-pole, rather than 4 (as originally posted). 4-pole generators in wind-turbines are more common in 50Hz countries, e.g. the venerable Vestas V-90 1.8/2.0 MW turbine uses a 4-pole generator for 50Hz and a 6-pole for 60Hz. Edit 2: There was a bit of confusion here (comments below). AC machines are just arrangements of iron and copper. The mechanical rotation of the shaft bears a fixed relationship to the frequency of the AC output (for a generator) or input (for a motor). In wind turbine DFIGs, clever electronics provide the illusion of asynchronous operation, but the machines themselves are unchanged and have "a synchronous frequency" despite being used in asynchronous service.
166 0 [deleted] [removed]
18 0 -NICX From experience on Enercon wind turbines, they run a direct drive synchronous generator. This generator, when operating at full output, is typically only turning about 17 rpm, and produces 400 volts, 3 phase power. The generator is wound manually in the factory and I believe each coil is 58 turns, and then 2 parallel coils per slot, (4 coils essentially), for the 2 MW machine.
26 0 leahcim165 Ok, what is happening in this thread? Why don't wind turbine enthusiasts understand how to answer a question? Instead, it's endless "oh, it depends on such and such variables" - duh! Everything does. We're asking what the TYPICAL NUMBER OF TURNS is. If someone asked, "how many transistors are there in a typical 2017 cpu" (it's about 1 billion), the people in this thread would endlessly say "it's impossible to determine" rather than actually using their knowledge to help inform.
3 0 mjss518 I think offering a calculated approximation can be done using the link provided...19rpm at 660V nominal output, and perhaps a built in transformer. http://img.directindustry.com/pdf/repository_di/51394/pdf-document-2mw-permanent-magnet-synchronous-gearless-wind-turbine-generator-110785_1b.jpg