Wind Turbine Components
Wind Turbine Parts
The principal parts of a modern wind turbine are the rotor, hub, drive train, generator, nacelle, yaw system, tower, and power electronics.
Both the Horizontal Axis Wind Turbine (HAWT) and the Vertical Axis Wind Turbine (VAWT) have similar sub-systems, except that the VAWTS do not have a yaw system, as they are not sensitive to wind direction.
Wind Turbine Subsystems
The major wind turbine subsystem are following
- Rotor: Blades and Hub
- Drive Train: Low-Speed Shaft (LSS), Bearings, Couplings, Gear Box, High-Speed Shaft (HSS), Brakes
- Electrical: Generator, Power Electronics
- Control: Pitch motor and gears, Yaw motor, gears and brakes, sensors (wind and direction)
- Support Structures: Tower, Nacelle
Rotor
- The blades and the hub together are called the rotor.
Blades
- Blades can be pitched and can have control surfaces (flaps).
- Blades can be twisted, tapered, and coned.
- Blade materials are Wood and cloth, Glass (reinforced) fiber polyester (GFP), Glass fiber epoxy (GFE), Carbon fiber epoxy, Wood epoxy, Aluminum, Steel (heavy)
Hub
Blades attached to the Hub. Hub options (from left to right)
- Rigid
- Rigid/pitching
- Teetering
- Hinged hub
Drive Train
Drive Train consists of the Low-Speed Shaft (LSS), Bearings, Couplings, Gear Box, High-Speed Shaft (HSS), and Brakes.
Low-Speed Shaft
- The low-speed shaft is also called the main shaft.
- Rotor RPM is low (30-60 RPM) and the torque is high.
- As the rotor size increases, the torque and moments correspondingly increase.
- The torque transmission path is identified as the “load-path”.
- The main/low-speed shaft is usually made of steel and must be able to carry very large torque loading.
- It transfers the torque from the rotor to the rest of the drive train, while also supporting the weight of the rotor.
- The main shaft is supported by bearings which transfer the reactionary loads to the main frame of the turbine.
GearBox
The gearbox connects the low-speed shaft to the high-speed shaft. It increases the rotational speeds from about 30 to 60 rotations per minute (RPM) to about 1500 to 1800 RPM, the rotational speed required by most generators to produce electricity.
The gearbox is a costly (and heavy) part of the wind turbine. Engineers are exploring “direct-drive” generators that operate at lower rotational speeds and do not need gearboxes.
Choices:
- Planetary or parallel
- Shaft bearing and location
- Number of stages
- Speed-up ratio
Gear System
Parallel and Planetary Gears
Parallel and Combined Parallel/Planetary
Drive Train Configurations
Double bearing layout (left) and Single bearing layout (Right)
Integrated bearing layout (left) and direct drive layout without gearbox (right)
Coupling
- Couplings connect the shafts together and transmit torque between the two shafts.
- Couplings can be effectively used to dampen torque fluctuations in the main shaft before power is converted to electricity.
- They are typically found between the main shaft and the gearbox, and between the gearbox output and the generator.
Brakes
- Turbines do not operate above certain wind speeds because they might be damaged by the high winds and associated loads.
- Brakes – A disc brake can be applied mechanically, electrically, or hydraulically to stop the rotor in emergencies, for maintenance, and when the threshold speed is exceeded.
Yaw System
Free yaw (typical in downwind/smaller turbines).
- The turbine automatically orients due to the aerodynamic loads on the blades.
Utility-grade turbines employ a yaw drive (gear-motor) and direction sensor (wind vane) to orient the rotor blades into the wind.
- The difference between the orientation of the rotor and the direction of the wind is used to activate the yaw motion.
A yaw motor, pinion gear, bull gear, and yaw brakes make up the yaw system.
- Yaw motor – Powers the yaw drive.
- Yaw drive – Upwind turbines face into the wind; the yaw drive is used to keep the rotor facing into the wind as the wind direction changes.
- Downwind turbines do not require a yaw drive, the wind blows the rotor downwind.
Generator
- Converts the (rotational) mechanical energy extracted into electrical energy using magnetic fields.
- Usually alternating current operated at a constant speed to produce utility-grade 60Hz AC power.
- Since induction-type generators draw large amounts of reactive power from the utility grid, compensatory capacitors are necessary.
Generator Types
- Induction generators (fixed RPM)
- Wound-rotor induction generator with variable rotor resistance (variable RPM)
Doubly-fed induction generator (variable RPM)
- The Doubly-Fed Induction Generators (DFIG) are more commonly used today.
- Efficient over a wider range of wind speeds.
- Minimizes gust induced power spikes in addition to being able to regulate voltage.
Permanent Magnet Direct Drive Generators
Nacelle
- The nacelle houses all the major components of a modern wind energy conversion system, except the rotor. The nacelle sits atop the tower.
- It is more of a protective cover for the components and is made of lightweight material.
- The nacelle does not carry any load and thus is not a structural member.
Towers
- Towers are generally made of galvanized steel (tubular) or lattice (truss). Portions may be made out of concrete as well.
- Smaller turbines can be supported with guy lines.
- The tower supports the nacelle and transmits static, and dynamic forces and moments to the foundation.
- Tower heights are usually of the same order as the rotor diameter.
- For modern turbines, the tower is the most expensive part.
- Tubular towers provide protected access to components in the nacelle.
Control Unit
- The main purpose is to limit the power extracted at high wind speeds (above-rated speed) and to start the turbine below that speed.
- High speeds typically happen only for a short time, however, if they are not controlled they can/will damage the drive train, gearbox, and generator.
- Aerodynamic control is the most effective form.
- Stall control (passive)
- Pitch control (active)
Anemometer
Anemometer – Measures the wind speed and transmits wind speed data to the controller.
Controller –
Controller
The controller starts up the machine at V, (wind speeds of about 8 to 16 miles per hour (mph)) and shuts off the machine at Vo (about 55mph). Turbines do not operate at wind speeds above because they might be damaged by the high winds.
Pitch Mechanism
Pitch mechanism – Gears housed in the hub are activated electrically or pneumatically. Blades are turned (or pitched) out of the wind to control the rotor speed and keep the rotor from turning in winds that are too high (or low) to produce electricity.
Transformer
Transformer – The power from the generator goes to a transformer, which converts the electricity from low voltage, around 480V, to the appropriate voltage for transmission, typically 33KV.
Wind Direction
Wind direction – An “upwind” turbine operates facing into the wind. Other turbines are designed to run “downwind,” facing away from the wind.
Wind Vane
Wind vane – Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind.