06-02-2013, 11:02 AM
Limiting factor on turbines, and why they have to be feathered in strong winds, is that the tips of the blades must not exceed the speed of sound at sea level - if they do, the shock wave created destroys the blade leading to the turbine being unbalanced & failing, potentially catastrophically... (see YouTube videos ad-nauseum where the braking system fails in high winds - quite spectacular!).
Typical modern industrial turbines have 40mtr to 90mtr diameter blades; Speed of sound at sea level is approx 340 mtrs/sec.
A 40mtr blade has a circumference of approx 125 mtrs, so at 163 RPM, the tips of the blades at at the speed of sound.
For a 90 mtrs diameter blade, the circumference is about 280 mtrs, so the max rotational speed is only 73RPM.
If the blades exceed this, the turbine will self destruct. The turbines have electrical and mechanical braking as well at blade pitch and yaw controls - they are complex. The generator itself is at the top to act as a counterbalance and to minimise energy loss between the blades, geartrain, brakes & turbine - the mechanics becomes a single rather than distributed package.
Power is generated using low, rather than high speed, torque so controlling blade speed to optimise torque to hit the generator sweet point is the name of the game.
On a domestic level, unless you are in some isolated croft in the Highlands, turbines make no sense whatsoever. CAT (Centre for Alternative Technology) , who have been advocating alternative energy for many many years, themselves told me that it far more efficient and cost effective to pay a bit more for "green" electricity generated on a commercial scale than to attempt to do it yourself - yes, you lose a bit of that warm & cuddly feeling, but I'd rather get it demonstrably right as opposed to trying to win brownie points at an ill-informed dinner party...
Typical modern industrial turbines have 40mtr to 90mtr diameter blades; Speed of sound at sea level is approx 340 mtrs/sec.
A 40mtr blade has a circumference of approx 125 mtrs, so at 163 RPM, the tips of the blades at at the speed of sound.
For a 90 mtrs diameter blade, the circumference is about 280 mtrs, so the max rotational speed is only 73RPM.
If the blades exceed this, the turbine will self destruct. The turbines have electrical and mechanical braking as well at blade pitch and yaw controls - they are complex. The generator itself is at the top to act as a counterbalance and to minimise energy loss between the blades, geartrain, brakes & turbine - the mechanics becomes a single rather than distributed package.
Power is generated using low, rather than high speed, torque so controlling blade speed to optimise torque to hit the generator sweet point is the name of the game.
On a domestic level, unless you are in some isolated croft in the Highlands, turbines make no sense whatsoever. CAT (Centre for Alternative Technology) , who have been advocating alternative energy for many many years, themselves told me that it far more efficient and cost effective to pay a bit more for "green" electricity generated on a commercial scale than to attempt to do it yourself - yes, you lose a bit of that warm & cuddly feeling, but I'd rather get it demonstrably right as opposed to trying to win brownie points at an ill-informed dinner party...
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