Basic Construction of Wind Turbine

Major Parts of Wind Turbine

Tower of Wind Turbine

Tower is very crucial part of wind turbine that supports all the other parts. It not only supports the turbine but raises the turbine to sufficient height so that its blades tips would be at safe height during rotation. Not only that, the height of the tower is so maintained that it can get sufficiently strong wind. The height of tower ultimately depends on the power capacity of wind turbines. The tower of the turbines in commercial wind power plants usually ranges from 40 meter to 100 meter. These towers may be either tubular steel towers, lattice towers, or concrete towers. The tubular steel tower are used for very large wind turbine. These are normally manufactured in section of 30 to 40 meter length. Each section has flanges with holes. Such sections are fitted together by nut bolts at site to form a complete tower. The complete tower is slight conical shape shape to provide better mechanical stability.

Lattice tower is assembled by different members of steel or GI angles or tubes. The all typical members are bolted or welded together to form a complete tower of desire height. The cost of these towers are much less than that of steel tubular tower but aesthetic look is not as good as steel tubular tower. Although, transportation, assembling and maintenance are quite easy but still use of lattice tower is avoided in modern wind turbine plant due to its aesthetic look. There are another type of tower used for small wind turbine and this is guyed pole tower. 

This is a single vertical pole supported by guy wired from different sides. Because of numbers of guy wires, it is difficult to access the footing area of the tower. Because of that this type of tower is avoided in agricultural field. There is another type of wind turbine tower used for small plant and this is hybrid type tower. This is also a guyed type tower but only difference is that instead of using a single pole in the middle it uses a thin and tall lattice type tower. This is hybrid of both lattice type and guyed type tower.

Nacelle of Wind Turbine

Nacelle is a big box or kiosk that sits on the tower and houses all the components of a wind turbine. It houses electrical generator, power converter, gearbox, turbine controller, cables, yaw drive.

Rotor Blades of Wind Turbine

Blades are the main mechanical parts of wind turbine. The blades convert wind energy into usable mechanical energy. When the wind strikes on the blades, the blades rotate. This rotation transfers its mechanical energy to the shaft. Blades are shaped like airplane wings. The wind turbine blades can be 40 metres to 90 metres long. The blades should be mechanically strong enough to withstand strong wind even during storm. At the same time the wind turbine blades should be made as light as possible to facilitate smooth rotation of the blades. For that the blades are made of fiberglass and carbon fiber layers on synthetic reinforce. In modern turbine, normally three identical blades are fitted to a central hub by means of nut bolts. Each identical blades are aligned at 120° to each other. This makes better distribution of mass and gives the system more smooth rotation.

Shaft of Wind Turbine

The shaft directly connected to the hub, is low speed shaft. When the blades rotate, this shaft spins with same rpm as the rotating hub. This shaft may be directly coupled to the electrical generator in case of low speed generator. But in most cases, the low speed main shaft is geared with a high speed shaft through a gearbox. In this way, the rotor blades transfers its mechanical energy to the shaft which ultimately enters to an electrical generator.

Gearbox

The wind turbine does not rotate in high speed rather it rotates gently in low speed. But most of the electrical generators require high speed rotation, to generate electricity at desired voltage level. So there must be some speed multiplication arrangement to achieve the high speed of the generator shaft. The gearbox of the wind turbine does this. Gearbox increases the speed to much higher value. For example, if gearbox ratio is 1:80 and if the rpm of low speed main shaft is 15, the gearbox will increase the speed of generator shaft to 15 × 80 = 1200 rpm.

Generator

Generator is an electrical device that converts mechanical energy received from shaft into electrical energy. Normally, induction generators are used in modern wind turbines. Previously, synchronous generators were popular for this purpose. Permanent Magnet DC generator also used in some wind turbines. The speed of the shaft can be made high by using gearbox assembly, but we can not make the shaft speed constant. There may be a fluctuation in shaft speed since it depends on wind speed. So, speed of the rotor of generator also varies. This variation affects the frequency, voltage of the generated electric power. To, overcome these issues, we normally use induction generator for the purpose. Because induction generator always produces electric power synchronized to the connected grid irrespective of the speed of the rotor. If we use three phase synchronous generator, then we first rectify the output power to DC and then convert it to AC of desired voltage and frequency by means of inverter circuit. This is because the alternating power generated by synchronous generator is not constant in voltage and frequency, rather it varies with speed of the rotor. Because, of same reason, in some cases we use DC generator for the purpose. In these cases, the output DC power from generator inverted to AC of desire voltage and frequency, before feeding it to the grid.

Power Converter

Because wind is not always constant so electrical potential generated from generator is not constant but we need a very stable voltage to feed the grid. Power converter is an electrical device that stabilizes the output alternating voltage transferred to the grid.

Turbine Controller

Turbine controller is a computer (PLC) that controls the entire turbine. It starts and stops the turbine and runs self diagnostic in case of any error in the turbine.

Anemometer

It measures the wind speed and passes the speed information to PLC to control the turbine power.

Wind Vane

It senses the direction of wind and passes the direction to PLC then PLC faces the blades in such a way that it cuts the maximum wind.

Pitch Drive

Pitch drive motors control the angle of blades whenever wind changes it rotates the angle of blades to cut the maximum wind, which is called pitching of blades.

Yaw Drive

Blades and other components in wind turbine is housed in nacelle, whenever any change in wind direction is there, the nacelle has to face in the direction of wind to extract the maximum energy from wind. For this purpose yaw drive motor are used to rotate the nacelle. It is controlled by PLC that uses the wind vane information to sense the wind direction.