Wind Glossary::::WindEdu:::::SolarEdu::::::PVApps


SolarSteve's

School of Terrestrial Wind Energy

:::Overspeed Protection:::

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:

- R.P.M. sensing logic circuitry together with centrifugally-activatedaerodynamic feathering.
- 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 wind.
&shyp; 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.

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Wind Glossary::::WindEdu:::::SolarEdu::::::PVApps



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