Design Wind Power Turbine - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 27

2.6 PowerControlofWindTurbines

Wind.turbines.are.designed.to.produce.electrical.energy.as.cheaply.as.pos-
sible.. Wind. turbines,. therefore,. are. generally. designed. so. that. they. yield.
maximum. output. at. wind. speeds. around. 15. m/sec.. (30. knots. or. 33. mph)..
Its. does. not. pay. to. design. turbines. that. maximize. their. output. at. stronger.
winds.because.such.strong.winds.are.rare.
In.case.of.stronger.winds,.it.is.necessary.to.waste.part.of.the.excess.energy.
of.the.wind.in.order.to.avoid.damaging.the.wind.turbine..Thus,.all.wind.tur-
bines.are.designed.with.some.sort.of.power.control..There.are.two.different.
ways.of.doing.this.safely.on.modern.wind.turbines.

2.6.1 Pitch-Controlled Wind Turbines

On.a.pitch-controlled.wind.turbine,.the.turbine's.electronic.controller.checks.
the.power.output.of.the.turbine.several.times.per.second..When.the.power.
output. becomes. too. high,. it. sends. an. order. to. the. blade. pitch. mechanism.
that. immediately. pitches. (turns). the. rotor. blades. slightly. out. of. the. wind..
Conversely,. the. blades. are. turned. back. into. the. wind. whenever. the. wind.
drops.again..Thus,.the.rotor.blades.have.to.be.able.to.turn.around.their.lon-
gitudinal.axis.to.select.the.pitch..During.normal.operation,.the.blades.will.
pitch. a. fraction. of. a. degree. at. a. time,. and. the. rotor. will. be. turning. at. the.
same.time. 6,7
Designing.a.pitch-controlled.wind.turbine.requires.some.clever.engineer-
ing.to.make.sure.that.the.rotor.blades.pitch.exactly.the.amount.required..On.
a.pitch-controlled.wind.turbine,.the.computer.will.generally.pitch.the.blades.
a.few.degrees.every.time.the.wind.changes.in.order.to.keep.the.rotor.blades.
at.the.optimum.angle.in.order.to.maximize.output.for.all.wind.speeds.
The. pitch. mechanism. is. usually. operated. using. hydraulics. or.

electro-mechanics.

2.6.2 Hydraulic Pitch Control

Hydraulic. pitch. control. for. wind. turbine. blades. is. possible. with. rotary.
unions.from.Deublin.(Waukegan,.IL). 8
Generating.steady.shaft.speed.on.a.wind.turbine.means.constantly.adjust-
ing.the.pitch.of.each.blade.to.accommodate.wind.variations..The.blades.con-
nect.to.a.huge.hub.mounted.to.a.shaft.that.turns.a.gearbox.and.a.generator..
Best.turbine.eficiency.calls.for.a.continuous.pitch.control.on.the.blades.
Blade. pitch. is. powered. by. either. an. electric. or. hydraulic. drive.. Electric.
pitch.control.uses.slip.rings.to.conduct.power.to.motors.rotating.in.the.hub..
Hydraulic.systems,.on.the.other.hand,.use.a.rotary.union.to.deliver.hydrau-
lic.power.to.the.drive.motor..The.industry.is.split.about.45.percent.electric.
and.55.percent.for.hydraulic.controls..The.advantage.of.the.hydraulic.control.