Protecting you wind turbine from excessive wind speeds.
It is a very rare occurrence that any wind turbine can withstand those huge gusts of wind that come along now and again. There are huge forces in the wind and even larger centrifugal forces in your blades that can tear your system apart. So you need some method of slowing your blades down once they reach certain speeds to protect your investment.
Quite a few systems use the generator or alternator for this. You can place a load on them (eg turn on a heater) to make them do more work. This usually does a good job of slowing down your blades. If your alternator is too small or the gusts too strong this can just burn out your alternator leaving nothing to slow it down and you needing to buy a new alternator.
It seems the preferred method is to turn the blades out of the wind. You can of course do this manually but you can't be there 24/7, 365 days a year just incase, so to have your system do it automatically is the only real option. There are two good choices for moving the blades out of the wind, either vertically or horizontally.
As you can see from the above diagram, a spring loaded hinge is placed below the device in the pole and a weight out the front. The spring and weight mean that the blades will normally sit upright, in the wind. If the wind gets strong enough, the top is forced back against the weight and hinge, pulling the blades up out of the wind and slowing them.
To get the spring right, in no wind, tip the blade back by hand as far as it can go and make sure it returns to the upright position. The weight is harder. You will need to experiment with this. You need enough weight to keep it down until the wind speed hits the right mark. This will take a while and you will probably need to wait for the right day with the right wind to make sure it is alright.
This one is a little harder to understand but works in the same way. The blades are centered a bit off the center of the pole (say 5cm) where the whole system pivots. Since they are off center, when the wind pushes on it naturally wants to swing to the side (since there is more pressure on side of where it swings than the other). In order to balance that out we place the tail on the other side of the tower, keeping the blades facing the wind.
Now, to move the blades out of the wind, we need to let tail swing to the side, removing the balance of pressure. Since the tail pivot is on an angle, it takes some force to move it off the balance position as you are lifting it as well as turning it. You can adjust the angle to get the correct point at which the tail starts to furl or you can use some springs to get it right. As with the other method, it will take some experimentation to get it right and the blades turning out of the wind at the right wind speed.