megawatt turbine questions

[matthew]

i have a few questions about megawatt turbines after visiting one of the large farms in colorado.  

-do these large turbines go from AC to DC back to AC power?  I was told the megawatt turbine used PM generators, so this would produce AC power to begin with and would make a lot of sense since this produced electricity is directed towards our AC electrical grid.  however something makes me think that you have to go to DC first so the original AC power produced can be transformed into the exceptable AC power within our power grid.  simply, what is required to get the electricity produced into our power grid?  can the phases, frequences, voltages, etc. all be manipulated in the original AC power and put in our power grid or does it have to go to DC first?

-how big are the magnets in megawatt turbines?  or are there just a large number of them?

-i know megawatt turbines employ gear boxes in between their rotors and generators to increase effeciency, but which is kept at a constant rate?  is it the generator so the electricity produced is more or less as constant as possible, or is it the rotor so as the wind increase the generator can spin faster and faster?

anyway thanks for the info,

matthew dunay

[wdyasq]

some, some, some do, some do that, lots yes and depends.

Varies and both and sometimes none.

Most but not all, output but not on all and sometimes.

Just about every thing is done in wind turbines, many have PM generators. Others are electrically excited. Some rectify, others feed directly into grid.  Some are gear drive but one of the new thoughts is direct drive with huge diameter generator and PMs.  The latest also uses variable pitch bades but many are stall controlled.  

One would need to look at each windturbine model as a seperate style to properly answer your questions.  And, first one would need the model.  

I am told many of the mills are an accounting and generating capacity project where utilities may burn more 'poluting sources' when they have 'green capacity'.  Or, that is what has been explained to me.  The automobile companies do similar things to meet the CAFE standards by producing a certain number of high mpg cars even though the cars are driven a lot less than the ones that are actually sold and are driven on the road.

Ron

[pyrocasto]

I was under the impression that most of the bigger turbines were excited/induction generators, which would not require PM.

Though, it wouldnt even have to be a matter of how big the magnets are, but how many. If you were using a 5 foot diameter rotor you could use the same size magnets as we are, or maybe a little bigger, and yet you would get an enormous amount of power. Then you can go into dual stators and 3 rotors if you wanted too. :-)

[dalibor]

hey, you maybe want at check this one out. it is apart of guided tour on www. windpower.dk.

http://www.windpower.org/en/tour/wtrb/indirect.htm