17 Wind Turbine Components and Their Functions Explained
In order to successfully convert wind energy to electricity, a Wind Turbine depends on its specified components or parts. Wind turbine components are discussed in this article along with their functions, in the order given below;
14-15). The Wind Vane and Anemometer
1). The Base or Foundation as one of the Wind Turbine Components
In most cases, the foundation of a wind turbine is installed deep in the ground, and cannot be seen above it. This is one of the most relevant parts of the turbine; whose function is to hold the entire structure upright and firmly in place.
In addition to supporting the weight of the wind turbine itself; the foundation helps to ensure that the turbine is able to withstand the intense pressure from high-speed winds. This means that it needs to be one of the heaviest and sturdiest parts of the turbine.
Wind turbine foundations are of different types. These types are often decided on the basis of the size and type of the wind turbine itself, among other factors which may be considered. In general, different types of foundations are used between onshore and offshore wind turbines.
When designing a foundation for onshore wind turbines, the main factors which are considered include the site location and conditions [15]. Asides these, the features of the turbine itself are usually considered, such as its size and weight.
The site conditions that determine how a wind turbine foundation will be designed include the geotechnical conditions (nature and bearing capacity of soils, groundwater depth, etc.) and land-use pattern.
Onshore wind turbine foundations may be concrete pile or slab design. The dimensions (width, depth) are also determined by the prevalent environmental conditions.
Parts of an offshore wind turbine are often designed slightly different from those of an onshore wind turbine. This includes the foundation. Offshore turbine foundations may be Monopile, Gravity-based, Jacket, Floating, or Tripod type foundations. Each of these is discussed briefly below;
*Monopile Foundation
As the name implies, monopile foundations consist of a single, vertical concrete structure imbedded deep in the ground. This structure may be composed of concrete or steel. Monopile foundations are often used for offshore wind turbines that are installed in relatively shallow water [9].
The advantage of this type of foundation lies in the fact that it has a very simple design, and can be installed without much complexity or environmental impact. Monopile foundation is also adaptable to both shallow and deep-water installations of various sizes.
However, the installation and maintenance of this type of foundation is generally associated with risks due to the fact that monopile foundations may not have a suitable center of gravity to withstand huge hydrodynamic pressure.
This means that offshore wind turbines with monopile foundations are more likely to collapse in extreme conditions, posing a significant threat to their surroundings.
*Gravity-Based Foundation
As the name implies, this type of foundation is designed to hold the wind turbine structure firmly in place, strictly by the force of gravity.
Gravity-based foundations are usually made from concrete and are imbedded with granular earth materials like stones and gravel which increase the weight of the structure.
This type of foundation is beneficial for offshore wind turbine because it is relatively cheap to construct and install. However, it usually requires dredging before it is installed; and can negatively impact the environment.
*Jacket Foundation
Jacket platforms for wind turbines, are composed of four legs, which are connected to each other by diagonal beams [17]. This type of foundation is also fairly stable, and is very suited to offshore conditions compared to other types of foundations.
Like the tripod foundation, jacket foundation is adaptable to various environmental conditions including loose and weak soils, and high-energy currents. However, their installation may disturb the marine environment, and may cause the disruption of habitats.
*Floating Foundation
Also known as semi-submersible foundation, the floating foundation is a good choice especially in locations where the sea floor is at great depth beneath the water.
Floating foundations are composed of a central buoy which is anchored by about three catenary cables. Each cable is equipped with a weight that helps to provide tension while securing the structure to the sea floor.
Wind turbines and wind farms which are installed with floating foundations, have a wider reach than their more rigid counterparts. Due to the mobile nature of such renewable technologies, they are also more able to capture the best winds available within their vicinity.
Floating foundations have much less environmental impact and do not significantly disrupt the site in which they are installed. They are also relatively easy to maintain. Although the concept of floating foundation technology was introduced in 1972 by Professor William E. Heronemus [8], it is still in its development stage.
*Tripod Foundation
The tripod foundation for offshore wind turbines provides a three-legged structure that provides a fairly reliable center of gravity. These three legs are usually bound to a column that is made from steel or concrete [12].
Tripod foundations may resemble tri-pile foundations, which are composed of three columns that bear the weight of the turbine. However, unlike the tripod, the three legs of tri-pile foundations are not bound together at their base. Rather, the legs of a tri-pile foundation are bound by a central (concrete or steel) column above their base. This differentiates the two types from each other.
Although they can be costly to install and maintain, tripod foundations have the advantage of providing much stability to the wind turbine [4]. They are also suitable across a wide range if environmental conditions, including weak and loose foundation soils, and high-energy underwater currents. For large turbines, the tripod foundation provides and economic option. However, they require significant amounts of maintenance to prevent scouring and corrosion.
2). The Tower as one of the Wind Turbine Components
In most wind turbines, the tower consists of steel which has a tubular or cylindrical shape and a height of about 50m to over 100m.
The tower is one of the parts of a wind turbine, whose design must be planned carefully, with due consideration of different factors such as the size and weight of the turbine, and the prevalent environmental conditions. It is generally agreed that the height of the tower of a wind turbine determines how much wind it will be able to capture, and hence its efficiency [6].
Taller towers are capable of reaching high-speed wind currents at high altitude. However, in turbine design, efforts are usually made to make the height of the tower to be equal to the diameter of the blades when rotating.
The tower of a wind turbine plays the important role or function, of bearing the rotor and the nacelle [5]. There are various types of wind turbine towers, which are selected based on the existing needs, and conditions. These types include the lattice tower, steel tubular tower, hybrid tower, guyed tower and concrete tower.
*Steel Tubular Tower
Composed of sections which are usually about 20-30 meters in length each [16], steel tubular towers are tapering upward in their geometry, giving them an overall conical shape. The sections are connected to each other securely, using bolts, forming a firm structure. Steel towers are the most common type which is used in wind turbines.
*Lattice Tower
The lattice tower is not very commonly used, due to the presence of other, more efficient types.
It is designed by welding different sections of the steel profile together. Lattice towers are relatively cheap to manufacture.
*Guyed Tower
Also referred to as ‘Guyed-Pole Tower,’ this type of turbine tower is relatively light and less expensive to manufacture and install. Guyed pole towers are composed of a single, central pole which is supported by a set of guy wires.
The light weight makes installation and maintenance of guyed pole towers to be less difficult. However, they have the disadvantage of poor accessibility, because guy wires can seriously affect the ease of navigation around the tower.
Guyed towers are also less stable than most other types. Their light structure makes these towers to be very vulnerable to damage and vandalism by both human and natural factors. Therefore, installing a wind turbine with a guyed-pole tower support, has some negative safety implications.
*Hybrid Tower
As the name implies, a hybrid tower is generally composed of a combination of the features of any two or more of the commonly-known types of towers.
Such a combination may be in the form of guyed and lattice tower characteristics, or any other possible combination. Hybrid towers are used in cases where the conditions and/or needs of the wind installation project are fairly complex, and cannot be met adequately by any of the conventional tower designs.
3). The Rotor as one of the Wind Turbine Components
Composed of the turbine blades and the hub which connects them at the center; the rotor can be described as the component of the wind turbine which is in charge of capturing and converting kinetic energy in the form of wind.
The rotor captures wind (kinetic) energy using the turbine blades,
The turbine blades are designed as airfoil-shaped, light, and resilient parts of a wind turbine. There are usually three of such blades, and they are usually efficient at capturing as much wind energy within their vicinity as possible. They are also designed to be fairly resistant, so as not to get damaged easily by intense winds.
When the blades capture wind, it uses the kinetic energy to achieve rotary motion. Because the three blades are connected at the center by the hub, their rotation is transmitted efficiently through a low-speed shaft, to the rest of the wind turbine system.
This transmission signifies a conversion of kinetic energy from wind, to mechanical energy that causes rotary motion of the parts of a wind turbine. We can therefore say that the rotor converts kinetic-mechanical energy.
4). The Low-Speed Shaft as one of the Wind Turbine Components
Directly connected to the rotor, the low-speed shaft bears its name as a result of the fact that the rotation speed and frequency produced by the rotor is usually slow compared to that which is needed to run the generator and produce electricity.
The low-speed shaft transfers the rotary motion (mechanical energy) of the rotor, to the gearbox which amplifies it to produce higher-frequency rotation for the generator. Usually, the low-speed shaft rotates at speeds of between 8-30 rotations per minute (rpm), and may reach speeds of 60 rpm in exceptional cases.
5). The Main Shaft Bearing as one of the Wind Turbine Components
The main shaft bearing of a wind turbine is designed to support the low-speed shaft, by effectively transmitting the rotary motion from the rotor, toward the gearbox. It is also designed to minimize friction between the (rotary) moving parts of the turbine.
Because of the position and function of the main shaft bearing, it must be designed to withstand large, changing magnitudes of radial and axial load. The main shaft bearing is connected directly to the low-speed shaft, and usually has speeds that range between 8 and 60 rpm as well.
The fact that the main shaft bearing is exposed to harsh conditions implies that this is one of the parts of a wind turbine which must be designed very carefully. Main shaft bearings are generally expected to last for a minimum of 25 years.
6). The Gearbox as one of the Wind Turbine Components
The gearbox is the component which occupies the position between the low-speed main shaft bearing, and the high-speed shaft.
Specifically, the gearbox plays the role of increasing the rotational speed (derived from wind energy and transmitted through the rotor and low-speed shaft) of the drivetrain, to a level which is sufficient to drive the generator and produce electricity.
A typical gearbox is composed of a set of interlocked gears that transfer and amplify the cyclic motion from the low-speed shaft. This setup implies that the gearbox is constantly exposed to large and irregular cyclic loads as a result of varying wind speeds.
The severity of cyclic stresses on the gearbox often leads to frequent failure and damage. Because of the important function of this component, the gearbox is one of the parts of a wind turbine which has undergone continuous modification and improvement over the years. Increased efficiency and resilience of the gearbox will ultimately lead to increased electricity output.
7). The High-Speed Shaft as one of the Wind Turbine Components
Unlike the low-speed shaft, the high-speed shaft rotates at relatively high speeds of a least 1000 rpm on the average.
This is because the high-speed shaft is directly connected to the gearbox. Its function is to transmit the increased rotary speed from the gearbox to the generator. This increased rotary speed is what drives the electric coil of the generator, and causes it to produce electricity.
The rotor, low-speed shaft, main shaft bearing, gearbox, high-speed shaft and generator, all constitute what may be referred to as the drivetrain of the wind turbine. All energy conversions and transmissions in a wind turbine, are handled by the drivetrain.
8). The Generator as a one of the Wind Turbine Components
Responsible for the conversion of mechanical energy to electricity, the generator is another example of the important parts of a wind turbine.
This component consists basically of an electric coil (usually made of copper) which is stationed within a magnetic field, such that it is under the influence of magnetism. By rotating this coil at high speed within the magnetic field, electricity is produced, through the process of electromagnetic induction [7].
The high-speed rotation which is needed to produce electricity is much higher than that which can be provided by natural wind (kinetic) energy through the rotor. For this reason, the rate of rotation is multiplied by the gear box, and the resulting mechanical energy is transmitted to the generator through the high-speed shaft.
There are different types of generators used in wind turbines. They include; the AC synchronous generator; the AC asynchronous generator (or alternator); and the DC dynamo.
9). The Nacelle as one of the Wind Turbine Components
Nacelle has the function of protecting all the parts of a wind turbine that are directly involved in converting kinetic energy from wind into mechanical energy, and then electricity.
This implies that the nacelle is simply a housing component [11]. The parts which it protects include the rotor, shafts, gearbox, generator and controller systems.
By enclosing these components in the nacelle, they are able to remain within a fixed and well-planned configuration. The nacelle is installed on top of the turbine tower and is usually very large, weighing hundreds of tons and stretching for more than 50 ft.
The design of a wind turbine is always such that the nacelle is accessible for maintenance or repairs. In most cases, this is achieved by installing a system of lifts, ladders, and other climb-assist technologies [3]. Some modern offshore wind turbines are equipped with a helicopter-hoisting platform on top of the nacelle to enable tools and personnel to be lowered onto the turbine for service purposes.
The yaw drive is another component which is usually positioned underneath the nacelle. It makes the nacelle and the turbine blades to revolve on the axis of the turbine tower to face the direction of the most favorable wind currents. This revolution of the nacelle and blades is often called ‘yaw motion’.
10). The Yaw Drive as one of the Wind Turbine Components
It is important to note that the yaw drive is found primarily in a horizontal axis wind turbine.
The function of this component, is simply to ensure that the nacelle of the turbine is constantly facing the direction of best wind intensity and speed. By doing so, the wind turbine is made to produce its maximal amount of electricity at every point in time [14].
Yaw drives move the nacelle and turbine blades about the axis of the turbine tower in a horizontal rotary fashion. This is what is described as yaw motion. The yaw drive, along with a series of brakes and bearings, constitute the yaw system.
11). The Pitch Control as one of the Wind Turbine Components
Adjusting the angular orientation of the turbine blades is the primary function of the pitch control system [10]. This function is very important, because it determines how much wind energy will be captured by the turbine blades, and prevents damage under extreme-wind-intensity conditions.
The pitch control system actively monitors the orientation of the blades and the condition of wind flow; using this information to continuously adjust the blades by rotating them, such that they remain effective and operate within safe limits.
12). The Braking System as one of the Wind Turbine Components
One of the parts of a wind turbine which is fully involved in safety insurance is the braking system.
The main function of the braking system of a wind turbine is to automatically stop the rotor from moving [13]. This is necessary when the wind speed is above safe limits, or when another part of the wind turbine is damaged or faulty. By stopping the rotor, hazards and damages are minimized or prevented.
Two kinds of braking systems can be found in a wind turbine. These are the aerodynamic and the mechanical braking systems.
Aerodynamic braking system is usually the main braking system in a wind turbine. It provides a relatively fast, efficient and effective way to stop the turbine, which involves turning the turbine blades to a 90-degrees position relative to the horizontal axis.
The mechanical braking system is less efficient than the aerodynamic system and usually serves as an auxiliary (support) braking system. However, the mechanical braking system rarely used in most wind turbines, as the safety function of stopping the turbine is usually well-handled by the aerodynamic braking system.
While the aerodynamic braking system is spring-driven, and works based on hydraulic pressure, the mechanical braking system works mainly by friction. Mechanical braking system in a wind turbine is usually composed of brake pads and a rotating disc which when clamped together, bring the blades of the turbine to a stop.
Mechanical braking system provides a means to bring the turbine blades to a complete halt, and is therefore preferred only when it is necessary to achieve this motive.
13). The Controller as one of the Wind Turbine Components
With regards to regulating the operations of the entire system, the controller is one of the most important parts of a wind turbine.
Basically, this component carries out power management, by supervising, assisting and coordinating the operations of the other parts of the turbine. The controller helps to optimize the power production of the wine turbine while minimizing the loads to which the system is subjected.
In order to achieve this, a series of computers are used to continuously gather data concerning the environmental conditions as well as the operational health of the turbine [2].
By the function of the controller, the turbine operates within defined limits of wind speed, which is usually between 8 to 55 miles per hour (mph). This ensures that the turbine remains productive and functions optimally without damage.
14-15). The Wind Vane and Anemometer as Wind Turbine Components
An anemometer and a wind vane are usually installed in wind turbines, as part of the safety and controller systems. Respectively, these components help to acquire data concerning the speed and direction of prevailing winds within the vicinity of the turbine.
The data acquired by the anemometer and wind vane are sent to the yaw drive and controller systems, which determine the mode of operation of the turbine.
16). The Transformer as one of the Wind Turbine Components
Although it is not a major component, we can hardly discuss the parts of a wind turbine without mentioning the transformer.
Basically, the transformer is an intermediary component, which occupies the important position between the turbine and the utility grid. The transformer’s function is to step-up (that is; to increase or boost) the output voltage of the wind turbine [1].
When electricity is produced by the generator, it comes at a relatively low voltage compared to that which is needed to transmit the power through electric lines without much loss in the process. By increasing the voltage output of a wind turbine, the transformer ensures that power is transmitted to (and distributed through) the utility grid, efficiently.
17). The Transmission System as one of the Wind Turbine Components
In wind turbines, the transmission system comprises of a series of electric circuits and cables (transmission lines) that convey the power output of the turbine (after its voltage has been stepped-up by the transformer) to the point(s) where this power is needed.
The transmission system is designed to reduce potential power losses to the barest minimum while transmitting the produced electricity. In several cases, the transformer is considered to be a component of the transmission system in a wine turbine.
Conclusion
Wind turbine components include;
*Base or Foundation;
*Tower; Rotor;
*Low-Speed Shaft;
*Main Shaft Bearing;
*Gearbox;
*High-Speed Shaft;
*Generator;
*Nacelle;
*Yaw Drive;
*Pitch Control;
*Braking System;
*Controller;
*Wind Vane;
*Anemometer;
*Transformer, and;
*Transmission System.
These components serve various functions as already described. In general, we can summarize the functions of the parts of a wind turbine to include
1). Wind capture,
2). Mechanical energy production,
3). Increase in rotary speed,
4). Electromagnetic induction and electricity generation,
5). Stepping-up of voltage output,
6). Transmission of power,
7). Control and regulation,
8). Management and safety assurance, and;
9). Environmental data collection.
Altogether, these parts and their functions result in the conversion of wind (kinetic) energy to mechanical energy, and then to electricity, through wind capture, rotary motion, and electromagnetic induction.
References
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