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Cheating The Grid? - Page 2

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Posted by BobG on May 8, 2009, 3:03 pm
 
Your windmill is producing 'wild ac' with freq proportional to rpm. If
you get that rectified to dc and feeding a grid tie inverter, then you
can expect the whole 10KW can be used.... but your example asked 'if
everybody is producing 240V at the same time, there isnt any voltage
difference, and no current flows', and that would be true if it was
dc. In an ac motor, the more load on the motor, the more current it
draws... the more phase lag there is on the shaft from the angle of
the magnetic field. If you try to turn the motor faster than it was
being driven, now it is generating, and the grid is the load, and the
harder you try to 'speed it up', the more current it generates back
into the grid, so its more of a phase thing than a voltage thing.

Posted by Mike on May 10, 2009, 9:11 pm
 
wrote:


It's more or less impossible to know what you are replying to, but
I'll assume it's my comment about DC wind generators and their
efficiency.  The vast majority of commercial large scale wind turbines
use multipole (and switchable multipole) AC generators driven through
a step up gearbox of around 1:50.  They *very* rarely use DC and
inverters which is a technology much more suited to small scale
turbines.


--

Posted by harry on May 11, 2009, 8:48 pm
 
The world's biggest windmill recently commissioned generates DC (7 Mw)
for the reasons I mentioned. It has no gearbox.
DC may well be the technology of the future with the advance of solid
statedevices
http://www.metaefficient.com/news/new-record-worlds-largest-wind-turbine-7-megawatts.html

Posted by harry on May 9, 2009, 6:22 pm
 
I used to service electro mechanical  electricity meters. (Worked for
the elctricty board) They go backwards if the two outer wires are
reversed. Or the current is reversed. They are merely induction motors
when all's said and done .  It was a well known wheeze for "fiddling"
the meter for those in the know

DC windmills  can be made to generate in lighter winds(ie over a
greater range of windspeeds) than the AC  type. Which is why you never
see domestic AC mills these days. (Together with the synchronisation
problems.)
Even the latest commercial ones tend to be DC. The latest monster in
Germany is DC.  God knows how they invertthe current this multi
megawatt device!

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