Score
Title
382
AskScience Panel of Scientists XVII
7363
I’ve read that when caterpillars are in their cocoons, they dissolve completely into goo; no original parts survive in the butterfly. How is the butterfly made from the goo? Is there an embryo that grows and uses the goo like a yolk sac? Or does the goo somehow arrange itself into new body parts?
104
How sustainable is our landfill trash disposal model in the US? What's the latest in trash tech?
16392
With all this fuss about net neutrality, exactly how much are we relying on America for our regular global use of the internet?
54
If tooth decay is just caused by the bacteria feeding and producing acid, would a person that just used listerine have the same dental health as a person that brushed without flossing?
16
Does boiling water in a low pressure atmosphere still kill pathogens?
16
My doctor says that chemotherapy works by specifically targeting rapidly-dividing cells, which is how it works to fight cancer and also why it has the side effects that it does. But how does it “know” which cells are rapidly dividing? And how rapidly is “rapidly”?
8
How mixable are different types of plastic? Like PET and HDPE?
15
How are isotopes used in nuclear physics Experiments isolated?
848
In 1996 NASA announced 'evidence of primitive life on early Mars'. In 2000, a second report supported the thesis. What happened next?
3
How are the needles for Atomic Force Microscopes made, and how can the tip be smaller than the atoms they are manipulating? What are their limitations?
8
How are the triple(or more) parachutes commonly seen on capsules returning from space kept apart?
3
What makes a laser shine in a straight line?
82819
Help us fight for net neutrality!
1
How do scientists determine the weight of huge (extinct) animals?
2
what's the difference between ZW and XY chromosomes, how did they evolve, and why are ZW organisms homogametic for males where XY organisms are heterogametic?
4
What's the current state of AIDS? Is it still basically a death sentence, or is it manageable? What are the consequences of getting AIDS nowadays?
1
What happened to the Global Cooling scare of the 1980's?
0
If a pipe was run from space straight into the ocean would water run up it and flow into space?
2
Can animals understand human body language like laughing or smiling?
2
Lithium batteries are being developed to power cars in response to the decline in fossil fuels, but will lithium eventually run out as well?
1
Question from my 4 year old sister, do other animals also get "Boogers"?
1
Is there any short-term geothermal or atmospheric effect that is caused by the sun heating one "side" of the earth at a time?
14
Could an electric vehicle stand a chance in a racing event?
23
If there is an ocean below the ice surface of Europa, is the ice shell buoyant? Geologically supported? Or is it kept in place by the distribution of gravity?
1
Is there a mathematical relationship between Moire patterns, Chladni plate vibration patterns, and the pattern formed by rings when making different cuts from wood?
2
Would readers of character based languages (e.g Chinese) experience dyslexia differently since they don't use strings of letters?
3
How to calculate eigenvalues in the Kirchhoff's thin plate model?
27
Do all individual atoms in a solid emanate their own blackbody radiation?
14
Is there anywhere other than Earth in the Solar system where you could see a total solar eclipse and/or total lunar eclipse equivalent?
4
How did we get solid matter from light? How did Photons and Electrons create solid matter in the early ages of the universe when everything was insanely hot?
3
Since the event at CERN that proved the existence of Higgs bosons/Higgs field, can we now see this event happen regularly now we know ‘where’ to look?
8
Why does turning on an electric blender in the kitchen cause my HD antenna signal to go out in a different room?
6
Can the human body survive breathing pure oxygen at lower pressures?
14
When beryllium-16 decays and produces 2 neutrons simultaneously, what happens to that dineutron?
6
How do we know the earth’s core is super hot and why is it so?
1
How does the pressure of the vacuum of space affect the ISS?
11184
From my kid: Can you put a marshmallow on a stick out into space and roast it with the sun?
3
Given that cerebrospinal fluid flows around the structures of the brain, would messenger chemicals from synaptic activity in one area be passed to, and alter synaptic activity in other regions of the brain?
9
How do we know what the tonsil does?
2
In a compound with an alkene and an alkyne, which would ozone cleave in an oxidative cleavage reaction?
206 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 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.
168 [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.
24 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.
4 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
209 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.*
84 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.
167 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.
25 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.
5 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