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:
>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.
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
> wrote:
> >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.
> 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.
> --
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
> On Thu, 7 May 2009 14:11:18 -0700 (PDT), harry
> >The same effect can be achieved with a simple induction motor a lot
> >more easily. Check out "assynchronous generators"
> >Your electricity meter (if it were the old fashioned "spinning disk"
> >type) would run backwards if you were putting power back in ,ie the
> >disk would go the "wrong way round". The full output of your
> >generator could be put into the grid
> UK domestic, commercial and industrial meters haven't been reversible
> for many years, in addition electronic ones will indicate in an
> unambiguous manner any attempt to wind back the reading by illegal
> customer connected generation.
> >Here in the UK you can legitimately do this & they will pay you for
> >the power you generate. (But at a much less rate than they charge!)
> No, if you select the appropriate supply company and for either
> wind,hydro or chp you will get paid for electricity you export AND you
> also get paid for ALL the electricity you generate even if you use it
> yourself. 5p/kWh for the former, 9.2p/kWh for the latter giving a
> total of 14.2p/kWh. The current price for import is 12.63p/KWh
> The same company also pays 28p/kWh for solar generated export.
> >Windmills can be made more efficient generating DC.
> Not really.
> --
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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>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.