Since high RPM/high voltage is directly related to a wind speed, let's say 40MPH for the Wintura 500, why can't a controller be made to sense this and switch on a "speed limiting relay" to either add a direct heavy load to slow it down or to even "tap the brakes" by shorting the windings together until the voltage drops?
Good question, this basically describes the braking action of the turbines we are using with the grid tie inverters. The 1000 watt unit I have from SWEA ( Holland ) which is a plug in type inverter uses two sets of dump load boxes to maximize the braking. This method also requires a much heavier wire ( minimum # 8 three strand ) to carry the heat that is created in the braking process back to the turbine. It works but really I would rather have a furling tail that takes my turbine out of heavy winds no stronger than 30 mph. Come to think of it if you have not made the hydro you require at 20 - 25 mph, I think you should start looking for a different turbine to use.
sorry forgot to mention that I have used the Windy 500 with that unit and I am presently using a Windy 750.
Some turbines do use this type of technology. I think there are some down sides to doing this. The first is that you run the risk of destroying the copper stator inside the generator. As you said, you can "tap the brakes" but this is essentially a dead short to windings in the generator. When REALLY high winds come, and they always do once in a while, you run the risk of burinng up the stator. Also, keeping your turbine straight into the wind in REALLY high winds adds a lot of stress on the blades. I think it is best to take the stress off them and let them furl out of the wind when the wind is screaming. The best thing for a small wind turbine would be to probably have both: Some mechanism to furl the turbine or pitch the blades out of the wind coupled with some type of brake. The brake can be for emergency situations and can be as simple as a stop switch (i.e. manually flipping the switch shorts the generator wires).
Thanks for the answers. One question .... if the blades are facing the wind, spinning or not, what MPH can they tolerate before they permanently deform? Ref the 35s. What can they take furled? Seems a "road" test could provide these answers and be very useful.
We have tested to 70 mph with no furling and there was no deformation of the blades. You do not have to worry about testing of the blades at extremely high wind speeds with the blades not spinning. Even if you have the generator at a dead short, the blades are going to start spinning. By the time the wind hits 35-40 mph, the blades are going to be really moving even if the generator is braked (shorted). If the unit is furled, the blades will be able to take incredibly high wind speeds without damage (greater than 70 mph wind). Although we have never tested this, I would say that in the fully furled position the blades could handle at least 100 mph wind and probably much more than that. I had a customer in Alaska tell me that his blades survived a wind storm with peak wind gusts of 92 mph and his wind turbine had no furling mechanism! While his blades and wind turbine did survive the storm, I do not recommend building a wind turbine in a high wind environment that does not have any overspeed protection.
