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DIY Wind Turbine - Is this a Hoax?
Rhythmtech:
Checking this blog this morning I came across this Wind Turbine
project. On closer inspection of the motor they were using I noticed it did not appear to be an "Old DC Motor" as they claim. Not to mention that in some of the pics you can see a rectifier attached and the cap leads going to a plastic box. I would think if they had come up with an excitation voltage scheme to generate the back EMF they need to make the inductive motor act as a generator it would be the most interesting part of the build. Anybody else think this is not on the level?
Simon:
there is a website that deals exclusively with home builds of wind turbines, it's feasible but there will always be hoaxsters
Rhythmtech:
EMF - Electromotive Force. Basically means electrons get moved around in moving magnetic field. Like the inductive flashlights you shake to charge. Back EMF in the application of a generator presents itself as the magnetic field in the stator or rotor, depending on design, countering the magnetic fields on the rotating stator or rotor inducing electrons to move around. If you don't have a permanent magnet motor, you must create the magnetic field electrically. This is very often done on alternators for cars, so it is not uncommon, however it requires some sort of circuit to induce the field until the motor begins to generate enough current to supply its own field then whatever surplus energy that is generated charges the battery.
A motor and a generator are quite similar in operation and design but opposite in function. Like anything involving electrons, ideal is generally only on paper. Since you have rotating magnetic fields you actually end up with both a generator and a motor. The function (motor/generator) is determined basically by which one is done most efficiently. I am sure I've over simplified it and I probably have an error in there somewhere, hopefully it is helpful.
tecman:
I do quite a bit with the wind and renewable energy business. Any standard polyphase induction motor will also function as a generator. You can read lots on induction generators on the web. The biggest issue is energizing it. If you apply power when it is stopped it will just spin as a motor. If it is spinning near its nominal RPM when you apply the power, as you increase the speed to synchronous speed and above it will start to generate power. Spinning faster than the synchronous speed is akin to the "slip" that a motor runs below synchronous speed. Basically as you try to increase the speed it will generate power. More speed, more power, just like a normal generator, but always within 10% or so of synchronous speed..
In commercial wind turbines, nearly all use induction machines (as they are called). Lowest cost and very reliable. In those applications, reduced voltages are applied as they come up to speed and this brings on the field and power quickly without any surge on power up. The trend, being tested by some, is to have a large polyphase synchronous machine with permanent magnets or excited rotor, rectified and fed to an inverter to power the grid. This scheme has advantages that they can provide better power (better control of voltage, frequency and reactance) which will be mandated by FERC for the grid. But many obstacles exist in making variable speed, high efficiency synchronous machines of this size (1 MW on up), so the market is currently developing.
Paul
tecman:
What you have drawn will not work. An induction machine (generator) will not generate power on its own as you have drawn. Only a "synchronous" machine (one with some sort of permanent magnet or equivalent). An induction machine will generate power if energized, ie hooked up the the power line, and spun faster than its normal speed. If you spin an induction machine as you have drawn, it will just freewheel.
http://en.wikipedia.org/wiki/Induction_generator
http://www.electrodynamics.net/documents/electrodynamics_power_gen2002.pdf
http://www.usmotors.com/products/profacts/1-204.htm
paul
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