I was driving down I65 this weekend and went through about a 10 mile
stretch of wind farm in Indiana. And I was wondering how they got all
that power back on the grid. Each one of those windmills has a
generator on top of it I assume. So each generator is generating an
alternating current, and no way in hell are all of those literally
thousands of generators going to be in phase... So I was wondering to
get the generated current back on the main grid efficiently dont they
have to have some kind of master controller to align the phase of all
those generators back to the timing of the main grid and lock it in?
If the phases were all random for those 1,000 windmills wouldn't there
be cancellation of the current flow when you try to pump it back to
the grid individually? Because by probability half the generators
would be out of phase with the other half and simply cancel each
others current flow. Or do they just time each generators phase angle
individually off a small control current from the grid, and let it
feed the grid right there?
Any electricians can shed some light on this?
Why not? All the other thousands of generators all over the country are.
Yes, they are in phase when started; the small amount (relatively) of
generation of each generator is effectively locked in by the grid.
In order to "parallel" the 3 phases, each A-B-C phase of the power
source (whether it's 100 watts or 1,000 megawatts, it makes no
difference) has to be in "synchronization" with the A-B-C phases of the
In large units, this used to be done manually by using what's called a
'synch' scope with a rotating arm (representing the phase angle of the 3
phases as one, in relationship to the phase angles of the system. When
they are at "unity", that is the arrow on the meter facing straight up,
the switchyard breaker is closed. Now, such can be done automagically w/
servomechanisms and online measurement.
When the generator goes on grid, the system "grabs", quite literaly, the
generator and the three phase angles move in harmony/synchronization.
The 'speed' of the turbine/generator, whether 1800 RPMs or 3600 RPMs is
then forced driven by the system and not the primary energy source
(wind/steam/whatever). No matter how much more steam (or water as in
hydro) you add, the speed will always stay the same. Which is how power
is increased because the additional input wind force, while not adding
speed, adds torque, which, by increasing the
DC field, increases megawatts.
(Not EE/electrician but NE w/ 30+ yrs working w/ power utilities)
So it appears that each individual generator would have to synch with
the grid on its own at that spot and feed the grid on its own at that
spot. Because if you tried to synch all the generators at once and
feed the grid from a collection of generators, a more distant
generator will be out of phase with a point a mile away that is being
used as the reference time simply because of the distance. Yes all
the blades were spinning at slightly different rates based on the wind
there I guess but that does not mean the generators are at different
RPM's if they have a transmission of sime kind or adjusters for the
prop blades, to keep the generator speed constant and some controller
that calculates available torque at that moment to control how much
the generator can be saturated.
I must have been passing through Meadow Lake I, II, III and IV farms
looks like a total of 500 MW. It was really a head turner for many
On 9/6/2011 5:59 PM, email@example.com wrote:
I don't think so...from the other poster's link to the utility's site
under the "How Does A Wind Turbine Work?" heading it says (in part)--
"..The fast spinning shaft turns inside the generator, producing AC
(alternating current) electricity. Electricity must be produced at just
the right frequency and voltage to be compatible with the utility grid."
Each does synch itself, but they're all tied to one (or at least a
relative few) common point(s); each one is not tied directly to the grid
but to a switchyard that is, in turn, tied to the transmission grid
itself (at least all the large farms around here are and I really can't
imagine there are any that aren't that way altho it is possible, I
suppose, but would be prohibitively expensive w/ all the switchgear that
way I think).
It's really no different than any other generator; the reactance of the
grid is so large compared to the inertia of the individual generator
that once it is on grid it is forced to stay in synch. This happens
essentially "for free" by the nature of the field once the initial synch
NB that the synchronization is important only at the point of
connection--what time lag there is from one portion of the grid far
remote from another is immaterial; the local reactance that the
generator field "sees" from its own connection is all that is of
Also with respect to your earlier observation that rotor speed may be
slightly different owing to local variations in windspeed; as noted that
translates into more/less torque (and hence MWe) but the generator shaft
itself remains at a constant rpm. There is, of course, gearing that
translates the slow rotor speed to the generator shaft.
The consistency of the generator speed comes from the internal feedback
of the field and is forced by the much larger reactive response of the
overall grid that the individual generator is simply too small
relatively to influence significantly on its own. Hence there isn't
need for the complicated logic you're thinking must be there; only while
the individual generator is disconnected from the grid is there any
actual control of the generator rpm in order to achieve initial
phase-matching; once it's then connected to the grid it simply follows
along. As described in my first response, this is the basic operation
the same as what happens w/ any other AC generator tied to the grid
whatever its size or power source.
Many conventional power stations have multiple turbine-generators;
Kingston Fossil in TN has nine separate boilers as a relatively small
example. There's no fundamental difference between that and the wind
farm; it's simply more of the same w/ more smaller individual units.
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