## How much power does a wind generator produce?

Anything about construction that doesn't fit into any of the above

### Re: How much power does a wind generator produce?

Found this link you might find useful: http://s4wsbox.com/?q=node/3
windgat
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### Re: How much power does a wind generator produce?

And I have a link for you:
http://www.arnoldmagnetics.com/mtc/calc_gauss_rect.htm
I've checked it out . . . it works
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

I used Gauss instead if grade (from http://www.magnetichold.net/rarearth.htm), and interestingly got slightly less of a linear correlation.

So I then used the link you posted, and calculated the gauss at a point in the middle of the stator. I got even less of a correlation! Maybe using grade directly is not so bad after all...
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windgat
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### Re: How much power does a wind generator produce?

windgat wrote: . . .So I then used the link you posted, and calculated the gauss at a point in the middle of the stator. I got even less of a correlation! Maybe using grade directly is not so bad after all...
You can't use that value on its own
Say you fly past the coils at 2mm distance.Then you need to know the gauss reading at +2mm, half-way down the coil, and at the end of the coil. But, because you use two magnets interacting on the coil, you must average-out the combined field strength.
Very roughly: the average fieldstrength of the combined magnets equals: 2x mid-coil strength (of one magnet) +10%.
Or more precisely: average fieldstrength = (2xG(2)+8xG(mid)+2xG(end))/6

I'll put a post on that (soon).
Regards
Cor
Greystoke
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### Re: How much power does a wind generator produce?

Thanks... but isnt that stil linear? I am looking for a correlation remember, not a calculation to give a result in certain units.
windgat
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### Re: How much power does a wind generator produce?

No,
You're using a parameter that only partially contributes to the coil response, hence you're own observation of a decreased correlation. The value I gave you is directly (and solely) responsible for the coil voltage, so the correlation should improve.
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

Which value is that?
windgat
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### Re: How much power does a wind generator produce?

Sorry,
I meant "formula": average fieldstrength = (2xG(2)+8xG(mid)+2xG(end))/6
You still need to work-out the G(2) and the G(end) to work out that average.
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

OK,
This is what I was referring to:

It's about two magnets flying past a coil, each at a 2mm distance. The fieldstrength inside the coil is the combination of the fields of each magnet (the red and the bue lines), and indicated by the dashed yellow line.

To find the AVERAGE fieldstrength, you need to know the field (of ONE of the magnets only, as they are symmetrical) at position 2, 10(midpoint) and 18 mm (end of coil).
Then do the folloqwing calculation: average fieldstrength = (2xG(2)+8xG(mid)+2xG(end))/6 (In this case that should be around 3500 Gauss)
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

Thanks. From what I can see the figure you get from that formula for average strength will be a linear function of magnet grade/Br?

What I am after is the simplest possible, zero based measure of magnet effectiveness, even if it an approximation.
windgat
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### Re: How much power does a wind generator produce?

windgat wrote:Thanks. From what I can see the figure you get from that formula for average strength will be a linear function of magnet grade/Br?
And size of the magnet.
The smaller magnets are strong close-up, but fade faster on distance. (So, the mid point will be much lower.)

PS: I understand what you are trying to do, and I support it. Simplicity is the hallmark of the master. Its just that this business can be pretty complicated.
The average strength (AS) inside the coil is important, because it will allow you to calculate its response (voltage).

Using rectangular magnets the way you do, the emf = 1e-7 x Windings x Magnet_speed(m/s) x AS x Magnet_length(mm).
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

There is another aspect about these coils that puts a limit to their overall size.
The problem is that if the outer windings of the coil is much bigger than the magnet, they'll start picking-up return field lines which affect the flux density, and which lowers the expected coil response. Even a 50% oversize can be quite significant. You can see that the outer windings in this example already pick-up a number of "full" returns that trigger no response in the coil.
Another point is that the closer you can get the magnets to the coils, the greater (substantially more than linear) the response.

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Cor
Greystoke
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### Re: How much power does a wind generator produce?

Great, thanks for interesting diagram. I am a bit confused however... I can't quite picture it.

It looks like one set of magnets and two coils? I (and most others) use one set of coils between two magnets. Two magnets (poles on broadest faces) would cause a very different looking field surely?

Also, the rotor plate (5 or 6mm steel in my case) would radically affect the field lines, and I don't see that being taken into account here.
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### Re: How much power does a wind generator produce?

Surely you have multiple turns, and turns on top of each other on a coil? The turns furthest from the centre are most subject to catching "return" lines, as indicated.
They're not two coils in the picture. It represents the "inner" layers and the "outer" layers of the same coil, showing how different these layers capture the field.

The steelplate? All I can tell is that it would concentrate the outer return lines closer to the magnet. I wouldn't know by how much, but it would certainly exasperate the effect.
Coils that are much bigger than the magnet - even by as little as 50% - become lesser effective.
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

Aha, thanks, I can picture it now - its looking axially towards the centre of rotation.

The peak power would occur when the magnet is directly over one of the legs. As shown, that looks like it is at the 'zero power' point, where it is not generating anything (zero crossing of AC wave).

The magnet on the opposite rotor seems crucial to include. From my very limited understanding of magnetism, that would 'suck' the field lines straighter, reducing the effect you are speaking of?
windgat
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### Re: How much power does a wind generator produce?

The two fields add-up. There is no true "distorsion". It just looks that way. For instance, in the centre, between the two magnets, the field is exactly twice the single strength. That also applies to the return field outwards from the centre line.

I can't be too certain, but I don't think it will make much of a difference.

Perhaps this picture may be helpfull.

Regards
Cor
Greystoke
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### Re: How much power does a wind generator produce?

Ok, interesting. Why have you changed the magnet shape? Here is what I would have thought is the configuration to model (shown at point of peak voltage for that coil leg).
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windgat
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### Re: How much power does a wind generator produce?

The response of the coil is in answer to d?/dt, the time variation (flux) of the fieldstrenth ?. Obviously the highest voltage can be expected when ? is highest over the same time change, which is obviously at the point when the highest flux is captured, ie: when the magnets are dead centre, and the highest fiedstrength is presented. The very next moment the flux will reduce, and d?/dt will turn negative, meaning the response goes through zero, and the signal changes sign.
So generally, the highest response is usually just before the change of sign. However, with rectangular magnets, the coil usually generate square waves, so the responses are flat(ish).

BTW: It's the only picture I had of a computor generated field display of two interacting magnets. It gives the general idea.

PS: Notice this is my 100th post. Do I get a reward
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

Wow... keep it simple for me, remember! Does that mean the diagram I posted shows the point of maximum voltage generated?

Yes you get a prize! You get the next 100 posts absolutely free of charge
windgat
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### Re: How much power does a wind generator produce?

windgat wrote:. . . Does that mean the diagram I posted shows the point of maximum voltage generated?

No,
In the position you drew, the coil will capture a considerable number of return lines, going down as the magnets approach centre. So its not the best position. The maximum voltage is generated when the magnets are dead-centre, just prior to going through zero.

PS: As for my reward: I'll have a few toots on your account.
I'll redeem them next time when I'm in CT.
Regards
Cor
Greystoke
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### Re: How much power does a wind generator produce?

Nice smiley!

I don't get it about the magnets. When the magnet is in between the two legs of the coil, surely the net effect is zero
windgat
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### Re: How much power does a wind generator produce?

No No,
Its the change over time of the fieldstrength that causes the coil response. Not the fieldstrength itself. Why do you fly the magnets past the coils? To create a flux in time of course. When is that flux greatest? When the maximum fieldstrength passes the centre of the coil.
The fact that the signal changes sign is neither here nor there. One moment the fiedstrength is still increasing, but the next its decreasing. So first the emf was positive (and increasing), but the next moment the emf changes sign and is decreasing in size as the magnet moves away.
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

So if a wire moves at a constant speed through a constant magnetic field, no current would be induced?
windgat
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### Re: How much power does a wind generator produce?

Correct
If the field is constant then there is no change in time, and so d?/dt = emf = zero

Oh, and . . . It's not current that's induced, it's voltage. V(emf) = -d?/dt = the time change of the field in Weber/second.
and it's not just a wire moving trough the field . . . it's supposed to be a closed loop.
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Cor
Greystoke
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### Re: How much power does a wind generator produce?

windgat wrote:
So if a wire moves at a constant speed through a constant magnetic field, no current would be induced?
Is it possible that you are confusing "induced voltage" with magnetic force on a current carrrying wire

According to some definitions, the term "Lorentz force" refers specifically to the formula for the magnetic force:
Fmag = q(vxB) = the force that acts on a current-carrying wire in a magnetic field. In that context, it is also called the Laplace force

It's an importent force to consider. If the coil carries current because there's a load attached, then this current opposes the magnetic field working as a brake. This will slow the turbine down, but . . .then the voltage drops, and so the current drops, allowing the turbine to speed-up again. It's self-regulating
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Cor
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