Wind Turbines

Jerry HudginsAnd

Joel Jacobs

Wind Resource Facts• Double the wind speed results in 8 times the

power!

• Wind speed is larger as you move higher above the ground.

• Doubling the area swept by the blades doubles the power captured from the wind.

Small Crane Unloading Large Crane

• Wind turbines are therefore generally designed so that they yield maximum output at wind speeds around 15 m/s (33 mph). It 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. All wind turbines are therefore designed with some sort of power control. There are two different ways of doing this safely on modern wind turbines.

Power Limiting • Stall control - the blade position is fixed but

stall of the wind appears along the blade at higher wind speed,

• Active stall control - the blade angle is adjusted in order to create stall along the blades, (blade turned into wind to create more stall)

• Pitch control - the blades are turned out of the wind at higher wind speed

Stall

• Power curve can be made smooth by active control (active stall or pitch)

• Stall control has an overshoot depending on blade design

Turbine Sub-systems

Electrical power

Supply Grid Power

transformer Power converter

(optional) Gearbox

(optional) Wind power

rotor

Power conversion & power transmission

Power conversion & control

Power conversion & control

Mechanical power

Power transmission

Generator

Wind Generators

• Synchronous – variable speed• Induction – variable speed or fixed speed

– Cage rotor – directly connected to ac system and operates at fixed speed or fully rated power electronics for variable speed

– Wound rotor – uses rotor resistance slip control for small speed ranges

– Doubly fed – wide speed operating range using power electronics

Variable-Speed Wind Turbines with Partially Rated Power Converters –

Doubly Fed IG• Slip rings make the electrical connection to the rotor. • If the generator is running super-synchronously,

electrical power is delivered to the grid through both the rotor and the stator.

• If the generator is running sub-synchronously, electrical power is delivered into the rotor from the grid.

• A speed variation of ±30% around synchronous speed can be obtained by the use of a power converter rated for 30% of nominal power.

• It is possible to control both active (Pref) and reactive power (Qref), which gives better grid performance, and the power electronics enables the wind turbine to act as a more dynamic power source to the grid.

• The DFIG system does not need either a soft starter or a reactive power compensator.

• The system is naturally more expensive compared to the direct-connected systems.

• Possible to save money on the safety margin of gear and reactive power compensation units, and it is also possible to capture more energy from the wind.

Fully Rated Power Electronics Converter Turbine-Systems

• The synchronous generator shown in (a) is a cage rotor IG.

• The synchronous generator shown in (b) needs a small power converter for field excitation.

• Multi-pole systems with the synchronous generator without a gearbox are shown in (c) and (d).

• The last system uses permanent magnets, which are becoming cheaper and thereby attractive.

• All four systems have almost the same controllable characteristics since the generator is decoupled from the grid by a dc link.

• The power converter to the grid enables the system to control active and reactive power quickly. However, the disadvantage is a more complex system with more sensitive electronic parts.

FULL RATED POWER ELECTRONIC INTERFACE WIND TURBINE SYSTEMS

• Cage induction generators and synchronous generators can be integrated into the system by full rated power electronic converters.

• A passive rectifier and a boost converter are used in order to boost the voltage at low speed.

• It is possible to control the active power from the generator. A grid inverter interfaces the dc-link to the grid.

• It is also possible to control the reactive power to the grid. • The system is able to control reactive and active power quickly and then

the turbine may take part in the power system control.

Skystream System Parts

• Foundation• Tower• Turbine

Smart Foundation

(good for towers up to 60’)

Pier Foundation

• Excavating, rebar, concrete

• Bolt Template• 28-day Strength• County Building

Inspection$4038.64

Foundation bolt assembly

Disconnect Switchgear

Bushings and bolt assembly for connecting turbine to tower.

Grounding wire connecting turbine to tower.

Ground wire from tower base to ground stake.

• Split Phase – commonly used in North

America for single-family residential and light commercial

• 3-Phase – Used in

industrial applications

Maintenance• From the ground, listen for abnormal

sounds when the turbine is operating in moderate winds.

• Perform visual inspection from the ground at least once per year with turbine off.– Check ground wire connection at tower and at

grounding stake if possible– Check for blade cracks or breaks (use

binoculars)– Check visually for damage to nacelle, nose, etc.