Yaw drive
Encyclopedia
The yaw drive is an important component of the horizontal axis wind turbine
s' yaw system
. To ensure the wind turbine
is producing the maximal amount of electric energy
at all times, the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. This only applies for wind turbines with a horizontal axis rotor. The wind turbine
is said to have a yaw error if the rotor is not aligned to the wind. A yaw error implies that a lower share of the energy in the wind will be running through the rotor area. (The generated energy will be proportional the cosine of the yaw error).
, an actuation mechanism able to provide that turning moment was necessary. Initially the windmills used ropes or chains extending from the nacelle to the ground in order to allow the rotation of the nacelle by means of human or animal power.
Another historical innovation was the fantail
. This device was actually an auxiliary rotor equipped with plurality of blades and located downwind
of the main rotor, behind the nacelle
in a 90° (approximately) orientation to the main rotor sweep plane. In the event of change in wind direction the fantail
would rotate thus transmitting its mechanical power through a gearbox (and via a gear-rim-to-pinion
mesh) to the tower of the windmill
. The effect of the aforementioned transmission was the rotation of the nacelle
towards the direction of the wind, where the fantail
would not face the wind thus stop turning (i.e. the nacelle
would stop to its new position).
The modern yaw drives, even though electronically controlled and equipped with large electric motors and planetary gearboxes
have great similarities to the old windmill
concept. They still use a means of mechanical energy “production” (i.e. electric motor), a method to increase the torque
(i.e. gearbox) and a gear-rim mounted on the fixed portion of the wind turbine
and in constant mesh with the output gear
of the said gearbox.
while requiring the minimal amount of maintenance
and perform reliably for the whole life-span of the wind turbine
(approx. 20 years). Most of the yaw drive gearboxes have input to output ratios in the range of 2000:1 in order to produce the enormous turning moments
required for the rotation of the wind turbine
nacelle
.
from the yaw drives to the tower in order to turn the nacelle
of the wind turbine
around the tower axis (z axis). The main characteristics of the gear-rim are its big diameter
(often larger than 2 m) and the orientation of its teeth
.
The gear-rims with teeth
on the outer surface have the advantage of higher reduction ratios in combination with the pinions as well as reduced machining
costs over the gear-rims with inner teeth
. On the other hand the former configuration requires the yaw drives to be mounted far apart from each other thus increasing the wind turbine main frame dimensions and costs.
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
s' yaw system
Yaw system
The yaw system of wind turbines is the component responsible for the orientation of the wind turbine rotor towards the wind.-History:The task of orientating the rotor into the wind was a complicated issue already for historical windmills. The first windmills able to rotate in order to "face" the...
. To ensure the wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
is producing the maximal amount of electric energy
Electric potential energy
Electric potential energy, or electrostatic potential energy, is a potential energy that results from conservative Coulomb forces and is associated with the configuration of a particular set of point charges within a defined system...
at all times, the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. This only applies for wind turbines with a horizontal axis rotor. The wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
is said to have a yaw error if the rotor is not aligned to the wind. A yaw error implies that a lower share of the energy in the wind will be running through the rotor area. (The generated energy will be proportional the cosine of the yaw error).
History
When the windmills of the 18th century included the feature of rotor orientation via the rotation of the nacelleNacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
, an actuation mechanism able to provide that turning moment was necessary. Initially the windmills used ropes or chains extending from the nacelle to the ground in order to allow the rotation of the nacelle by means of human or animal power.
Another historical innovation was the fantail
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
. This device was actually an auxiliary rotor equipped with plurality of blades and located downwind
Windward and leeward
Windward is the direction upwind from the point of reference. Leeward is the direction downwind from the point of reference. The side of a ship that is towards the leeward is its lee side. If the vessel is heeling under the pressure of the wind, this will be the "lower side"...
of the main rotor, behind the nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
in a 90° (approximately) orientation to the main rotor sweep plane. In the event of change in wind direction the fantail
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
would rotate thus transmitting its mechanical power through a gearbox (and via a gear-rim-to-pinion
Pinion
A pinion is a round gear used in several applications:*usually the smallest gear in a gear drive train, although in the case of John Blenkinsop's Salamanca, the pinion was rather large...
mesh) to the tower of the windmill
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
. The effect of the aforementioned transmission was the rotation of the nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
towards the direction of the wind, where the fantail
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
would not face the wind thus stop turning (i.e. the nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
would stop to its new position).
The modern yaw drives, even though electronically controlled and equipped with large electric motors and planetary gearboxes
Epicyclic gearing
Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...
have great similarities to the old windmill
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
concept. They still use a means of mechanical energy “production” (i.e. electric motor), a method to increase the torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
(i.e. gearbox) and a gear-rim mounted on the fixed portion of the wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
and in constant mesh with the output gear
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
of the said gearbox.
Types
The main categories of yaw drives are:- The Electric Yaw Drives: Commonly used in almost all modern turbinesWind turbineA wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
. - The Hydraulic Yaw Drive: Hardly ever used anymore on modern wind turbines.
Components
Gearbox
The gearbox of the yaw drive is a very crucial component since it is required to handle very large momentsTorque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
while requiring the minimal amount of maintenance
Maintenance, Repair and Operations
Maintenance, repair, and operations or maintenance, repair, and overhaul involves fixing any sort of mechanical or electrical device should it become out of order or broken...
and perform reliably for the whole life-span of the wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
(approx. 20 years). Most of the yaw drive gearboxes have input to output ratios in the range of 2000:1 in order to produce the enormous turning moments
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
required for the rotation of the wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
.
Gear rim and pinions
The gear-rim and the pinions of the yaw drives are the components that finally transmit the turning momentTorque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
from the yaw drives to the tower in order to turn the nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
of the wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
around the tower axis (z axis). The main characteristics of the gear-rim are its big diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
(often larger than 2 m) and the orientation of its teeth
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
.
The gear-rims with teeth
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
on the outer surface have the advantage of higher reduction ratios in combination with the pinions as well as reduced machining
Machining
Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...
costs over the gear-rims with inner teeth
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
. On the other hand the former configuration requires the yaw drives to be mounted far apart from each other thus increasing the wind turbine main frame dimensions and costs.
See also
- Wind turbineWind turbineA wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
- WindmillWindmillA windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
- Yaw bearingYaw bearingThe yaw bearing is the most crucial and cost intensive component of a yaw system found on modern horizontal axis wind turbines. The yaw bearing must cope with enormous static and dynamic loads and moments during the wind turbine operation, and provide smooth rotation characteristics for the...
- Yaw systemYaw systemThe yaw system of wind turbines is the component responsible for the orientation of the wind turbine rotor towards the wind.-History:The task of orientating the rotor into the wind was a complicated issue already for historical windmills. The first windmills able to rotate in order to "face" the...
- Wind powerWind powerWind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....
- Wind turbine designWind turbine designWind turbine design is the process of defining the form and specifications of a wind turbine to extract energy from the wind. A wind turbine installation consists of the necessary systems needed to capture the wind's energy, point the turbine into the wind, convert mechanical rotation into...
- Electric motorElectric motorAn electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
- Gearbox
Further reading
- Wind Power Plants, R. Gasch and J. Twele, Solarpraxis, ISBN 3-934595-23-5
- Wind Energy Handbook, T. Burton [et al.], John Wiley & Sons, Ltd, ISBN 0-471-48997-2