On Jan 5, 2009, at 4:38 PM, [email protected] wrote:
In reply to Horace Heffner's message of Mon, 5 Jan 2009 15:09:03
-0900:
Hi,
[snip]
Alaska often has sustained high winds, hurricane force, at high
elevations. Windmills built along mountain ridges could produce vast
amounts of energy. One problem is avoiding shutdown during peak
energy production periods. This can be accomplished by providing an
additional set of small diameter high wind speed turbines that do not
have to be feathered.
...or possibly either making the blades of normal turbines somewhat
retractable,
or not completely feathering them? (One would think that the latter
option would
be obvious - there must be something wrong with it).
Regards,
Robin van Spaandonk
Yes, I would think a reversible pitch blade would be stoppable in
high winds, but I guess it is not that simple. I know there have been
problems stopping wind mills whereby the brakes burned out.
Sometimes it happens due to warping blades, icing, or equipment
failure. Continuing to run the blades at near full power places them
at near critical torque for the brakes, so if things periodically get
briefly out of hand the brakes wear out. Wind gusts occur
frequently, so blade response has to be fast due to the cubic power
vs wind speed relation. If the blades are feathered early they can
be locked until the high wind conditions go away, thereby protecting
the brakes. An automated system might have some difficulty
distinguishing a brief gust from a sustained increase in wind
velocity so it can be a complex task, and energy consuming as well as
weight and cost adding, to be able to reduce the blade pitch in time
if it is operating in generating mode. Small light blade systems
have spring loaded automatic feathering which apparently can work
sufficiently fast and reliably up to a point, but I gather it is a
much more difficult job to feather large diameter turbine blades.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
