:::renewable energy education:::solar energy
School of Terrestrial Wind Energy
invites you to consider
Historically, nearly all wind generators have employed some
typeof overspeed control to insure against motor damage and electrical
overload.Without such built-in protection, wind systems would
physically fly apartin high velocity winds, victims of their own power.
The power-limiting featureis generally designed to operate when the
machine reaches its rated output,usually around 25 m.p.h.
Overspeed protection designs generally use a combination of tail
controland/or feathering. Tail control turns the propellor partially or
completelyout of the wind, above rated velocity, while feathering slows
the rotationalspeed through the use of cams or weights-and-springs on
the rotor, or bybraking the alternator dynamically.
In the past, centrifugal blade pitching was used most frequently as a
featheringmechanism. The Jacobs brothers attached weights to the
propellors. As theprop speed increased, the weights flew outward and
pulled at the blades,changing their angle of attack so that they no
longer caught the full forceof the wind. Other wind plant designs
incorporated mechanical air spoilersat the hub or blade tips for
overspeed control. These were generally mechanicallyactuated devices
which changed position at a predetermined speed to air-brakethe rotor.
More modern designs may use the best of the "first generation"overspeed
controls, adding additional safeguards:
sensing logic circuitry together with
- employment of patented dynamic braking circuits which sense R.P.M.
andgenerator output frequency, applying a short circuit on the
generator fora brief period, which effectively loads the propeller to a
point of rapidslowdown.
- use of an electronically-actuated tail control; a small servomotor
controlfolds the tail horizontally, turning the generator out of the
­p; integrated spring-loaded tail which may either fold in a
horizontalplane as the winds accelerate, or tip the generator up and
out of the wind.
"The road to Carbon Emission Reduction is always