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Alternators vs. Generators for wind power - Page 6

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Posted by amdx on July 8, 2008, 4:20 pm
 


  I will add, But can only find one reference,
"In terms of frequency, a 60 hz transformer driven a 20 hz will draw too
much magnetizing current and will run dangerously hot."  So I would not just
grab a standard power transformer unless you are aware of the frequency
range of your alternator.
                              Mike





Posted by Johnny B Good on July 8, 2008, 8:31 pm
 



====snip====


 That's true when the 60Hz rated voltage is applied but when only one
third of that voltage is applied at 20Hz, the magnetization current
remains the same (see below)


 That paragraph above, basically, restates that once you've ascertained
the open circuit generator voltage for a 60Hz speed, you can connect it
to a 60Hz transformer winding (a tapping on either a primary or
secondary, it matters not, provided it is rated to handle the power from
the generator running at 60Hz speed) with a voltage equal to or greater
than that voltage.

 From then on, whatever the frequency of the PM alternator, the voltage
will vary in direct proportion. A simple example should make this clear:

 Your PM alternator testing has revealed a 60Hz O/C output voltage of
60v and you select a 240v 500VA mains transformer with a 60 volt
secondary (which will be used as the primary in this configuration).
When the alternator runs at 1/3rd of the 60Hz reference speed not only
is the frequency reduced to 20Hz but,likewise, the voltage is reduced to
20v resulting in the same magnetization current in the transformer. All
that's changed is that the transformer is now only able to handle one
third of it's rated power (a neat match to the same reduction of your PM
generator's output power).

 That takes care of the magnetization current issue but there is also
the maximum line voltage issue to contend with. With a wind driven PM
alternator, you have a minimum and (most important) a maximum useful
output voltage range to contend with. If the maximum speed before
shutdown corresponds to 60 to 80Hz then you can base your choice of
transformer on the magnetization current considerations alone. However,
if the upper speed corresponds to 120 to 160Hz, you'll need to change
the "secondary" winding voltage selection from the 60v in the example to
120v to avoid producing line voltages in the region of 500v on a 240v
rated primary (although a large 500VA 240v transformer might be able to
take such voltage abuse in its stride, it's best not to push the voltage
much beyond the 300v mark)

 IOW, provided you have characterised your wind driven PM alternator
setup, it's perfectly possible to specify suitable 60Hz transformers for
such use.

--
Regards, John.

 Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.


Posted by Bruce Richmond on July 8, 2008, 3:24 am
 On Jul 7, 2:51pm, phil-news-nos...@ipal.net wrote:

My take has always been that an alternator produces alternating
current because it uses a solid slip ring which produceces ac
current.  That ac current is then rectified to dc.  It can also refer
to a magnet spinning in a coil which also produces ac current which is
rectified to dc.  A generator uses a split comutator to produce dc
current directly.  Whichever is used the car/motorcycle wiring sees
only dc current so it doesn't affect wire size.


Bruce

Posted by amdx on July 8, 2008, 2:43 am
 
   Well, a very qualified yes, but you not likely to have 140vac out of your
alternator and then transform, rectify and regulate it down to 14vdc to
charge your battery. But if you did you would reduce your wire losses by a
factor of 8 or 9. Or at least be able to reduce your wire size.
  I think it may be problem for the transformer, I suspect the frequency out
of the alternator varies with the wind, so it would need to operate at low
frequencies and high. I have no idea what the low and high frequencies would
be.
  I don't know much about wind power alternators, Are they single phase or 3
phase,
ac or dc. But then all that is probably true, just depends on the size,
model, and manufacturer.
                   Mike



Posted by z on July 8, 2008, 2:52 am
 

That windblue PM alternator/generator/whateveryoucall I use on my hydro
setup has the standard DC and an AC plug as well.. never tried it.  

But you can have both options on the same unit it seems.

They sell a kit with rectifier and connections for using the AC output
option:

http://www.windbluepower.com/product_p/ac-kit.htm

I think the purpose of this is to do just what you said Ulysses -- run
higher voltage over cheaper wires and then deal with it on the other end.  
You can imagine a tall assed wind generator might need quite a long run
of heavy wire using DC.. spendy.

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