In reply to Horace Heffner's message of Tue, 6 Jan 2009 00:01:04 -0900: Hi, [snip] >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/
I wonder if increasing the mass of the blades would help by adding/increasing the flywheel effect? It would certainly even out the very short wind gusts, and that would decrease the criticality of response time of other systems. Of course heavy blades would be harder to get moving initially, and hence would probably be better suited to higher wind environments. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
