How commercial wind generators work?

[devil2000]

I heard a theory that commercial wind generators from 100KW to 1MW are built without magnets, because magnets are expensive so alternator-like design for generators are used, but there are small generator with magnets so he can produce electricity for starting big generator.

If that is true, then why not there are some schematics for diy small wind turbines without magnets so can everybody can reduce cost of their generators ?

[Norm]

Without magnets we'd be back to square one,

bigger, heavier, machines, probably not as

efficient, and a lot more copper to offset

what you save in magnets.

[imsmooth]

Look up induction generator and squirrel-cage generator.

See http://www.awea.org/policy/documents/AWEA_Electrical_Guide_to_Utility_Scale_Wind_Turbines.pdf

[Flux]

Induction grid tie machines don't use magnets in the common form but there is still a magnetic field in action.

Large commercial alternators normally use ELECTRO magnets, still magnets but produced by a field coil with current passing through it. Some large commercial turbines are being produced with neo magnets. The cost is high and they present handling difficulties but they can provide higher output for a given size than the electro magnet machines.

Wound field ( electro magnet) machines are normally brushless with a rotating rectifier. The exciter may be permanent magnet but normally it is a wound field machine. A permanent magnet generator is sometimes provided as a pilot to excite the main alternator field.

So yes your description can be correct in some cases.

Until about 15 years ago virtually every wind turbine generator used wound fields and it can still work. You end up with a larger machine and you loose the power needed to excite the field, this can be up to 10% and that plays havoc with low wind performance.

I made a few machines with a pmg for light winds but used a wound field for the high wind conditions, this worked about as well as you could hope for in the days before neo but the things were heavy and the magnet steels used in the pmg were expensive so with the availability of decent permanent magnets these schemes went out of use.

For the small machines we deal with neo is really not that expensive when you consider the copper and iron you save. Wound field machines are not really a build it yourself option unless you have a lot of facilities.

Flux

[scoraigwind]

Ferrite (or 'ceramic') magnets were used widely in small wind turbine designs in the 1980s and many manufacturers of machines around 1-10 kW still use them.  For example the Bergey Excel uses them (although I hear rumours that this might change) and Proven use them. Marlec use them for their little turbines.

Ferrite magnets are now very cheap.  They are very robust and easy to use.  I have built a few turbines using ferrites and They have lasted much better over the years than the ones built with neo magnets.

Ferrite magnets are much less strong than neos, so you need to use a lot more turns of copper wire in the coils and the internal resistance is much higher.  This means that you cannot get such high output currents in strong winds,  and also the short circuit brake is not nearly so effective.  But in low winds you can get good results, and as the wind gets stronger there is no problem of the blades stalling due to low speeds as is the case with neo magnets.

You can find my old plans for building a turbine with ferrite magnets all over the web, and you can pay money to buy pirated copies off ebay.  Here on my site you can get the old PMG plans free for nothing.  http://www.scoraigwind.com/download/index.htm

Now I would take a simpler approach to the construction of the stator.  And there are a lot of other improvements in my newer plans but actually the use of ferrite magnets was a good idea that I have left behind, and might return to in the future, so as to get cheaper more reliable wind turbines.

[jlt]

 I made a wind turbine back in the nineteen seven tee,s. that was built from a 5hp 3phase motor. I used a solid steel shaft with 4pole electromagnet.that had slip rings .it really wasn't very hard to build .I cant seem to find the article any more. but a similar article was in home power #1. If my memory is correct mine put out 5amps and 13v at only60 rpm    

[joestue]

Its not because magnets are expensive, but because the required frequency converter is expensive.

KVA scales to the 4/3rds power of device volume, generator topology becomes a blur when you look at the big picture.

[Flux]

Yes Hugh, time flies when you get to my age, my guess of 15 years was way off, probably 30 years was nearer the mark.

Certainly no progress was made with magnet steels they were too expensive and very poor. Even Ferrite was very expensive in the early days but it was the first material to seriously challenge the wound field machines. Ferrite does have its advantages and the fact that it is physically virtually indestructible and doesn't rust is a very real one.

Flux

[s4w2099]

I do not know about the magnets but sure the inverter for a PMA machine in the megawatt range is a challenging one to design and build properly.

It is new technology and not every one has it. Maybe the reason why still up to this time you can only see a handful of BIG commercial PMA machines.