Table of Contents
Overview
A modern wind turbine is a machine that converts the kinetic energy of moving air into electrical energy. It does this through a chain of components that capture, transmit, convert, and control energy, and finally deliver electricity to the grid. Each component has a specific role, from the blades that feel the wind, to the generator that produces electricity, to the control systems that keep everything safe and efficient.
In this chapter, the focus is on what the main components are, where they sit on the turbine, and what they do. Detailed aerodynamic or grid integration issues are treated in other chapters.
Main Structural Parts
A typical horizontal axis wind turbine has three major structural sections: the foundation, the tower, and the nacelle with the rotor on top.
The foundation anchors the turbine to the ground or seabed. Onshore, this is usually a large reinforced concrete base that spreads the loads into the soil or rock. Offshore, foundations can be monopiles, jackets, gravity bases, or floating structures, depending on water depth and seabed conditions. The foundation must withstand strong winds, turbine rotation, and in offshore cases, waves and currents.
Above the foundation stands the tower. The tower supports the nacelle and rotor at a height where winds are generally stronger and more uniform. On modern large turbines, tower heights commonly range from 80 to more than 150 meters. Towers are often tubular steel sections, although concrete, hybrid steel concrete, lattice, and wooden designs are also used. The tower carries static loads from the weight of the nacelle and rotor and dynamic loads from wind forces and turbine rotation, and it must limit vibrations to protect the machinery and ensure comfort for maintenance crews.
At the top of the tower sits the nacelle. The nacelle is a housing that contains most of the mechanical and electrical components, such as the main shaft, gearbox, generator, and control assemblies. It also includes equipment for yawing, braking, and cooling. The nacelle must protect these components from weather, allow cooling, and provide safe access for technicians.
Rotor, Blades, And Hub
Facing into the wind is the rotor. The rotor is the main energy capturing part and consists of the blades and the hub that connects them.
Most modern turbines have three blades. The blades are shaped as aerodynamic profiles that generate lift when wind flows around them. This lift force causes the rotor to turn around its axis. Blades are typically made from composite materials such as fiberglass reinforced plastic or carbon fiber, which combine high strength, stiffness, and relatively low weight. Inside, they often have spars or beams to carry loads, and they are designed to handle bending and twisting forces over many years of operation.
The length of the blades determines the swept area of the rotor, which is the circular area the blades cover as they rotate. The swept area is crucial because the power available from the wind is proportional to this area. If $R$ is the rotor radius, the swept area is
$$A = \pi R^2.$$
For a given wind speed, larger rotor radius means larger swept area and therefore a much higher potential power capture.
Each blade usually has a pitch mechanism at its root, close to the hub. Blade pitch is the angle of the blade relative to the wind. By rotating each blade around its longitudinal axis, the turbine can control how much aerodynamic force is generated. Pitch control is used to optimize power production at different wind speeds and to reduce loads or stop the turbine in high winds.
The hub is the central part of the rotor to which the blades are attached. It transfers the torque from the blades to the main shaft inside the nacelle. For pitch controlled turbines, the hub houses the pitch bearings and actuators, which are electric or hydraulic systems that adjust the blade angles. The hub itself must be very strong, since it carries the combined loads from all blades.
Main Shaft, Bearings, And Drive Train
The mechanical connection from the rotor to the generator is known as the drive train. Its central element is the main shaft. The main shaft, sometimes called the low speed shaft, connects the hub to the gearbox or directly to the generator. It rotates at the same speed as the rotor and must carry high torque, since the wind power is delivered at low rotational speeds.
Supporting the shaft are main bearings. These large bearings allow the shaft to rotate smoothly while carrying heavy loads. They must handle radial loads, parallel to the shaft, and axial loads, along the shaft, and also dynamic forces from turbulence and changing wind directions. Proper lubrication and sealing are essential to ensure long life and low friction.
In many turbines, between the main shaft and the generator sits a gearbox. The rotor turns relatively slowly, often around 10 to 20 revolutions per minute on large turbines, but most generators are more efficient at higher speeds. The gearbox increases rotational speed from the low speed shaft to a high speed shaft that drives the generator. It is a complex mechanical component with multiple stages of gears. Gearboxes are heavy and require careful design, lubrication, and cooling.
Some modern turbines use direct drive designs without a gearbox. In those, the generator is designed to operate efficiently at low speeds, so the rotor can connect more directly to the generator. This reduces the number of moving parts in the drive train but requires a larger, often heavier generator.
Generator, Power Electronics, And Electrical System
The generator converts mechanical power from the rotating shaft into electrical power. The most common generator types in wind turbines are induction and synchronous generators, with variations such as doubly fed induction generators and permanent magnet synchronous generators. Regardless of type, the generator must deliver electricity at controlled frequency and voltage, even though wind speed and rotor speed vary.
Since the wind is variable, modern turbines use power electronics to condition the electrical output. Power electronic converters adjust voltage, frequency, and phase so that electricity can match grid requirements or local loads. They also help control the generator torque and rotor speed, which allows better overall turbine control and efficiency.
Cables carry electrical power from the generator and converters down through the tower, often via a flexible loop that allows the nacelle to rotate without twisting the cables excessively. Within the turbine, there is also an internal electrical system that supplies auxiliary power for controls, yaw motors, pitch systems, lighting, heating, and safety systems.
At the base of the tower or nearby, there is usually a transformer. This device steps up the voltage from the level produced by the turbine to a higher level suitable for collection networks and transmission systems. Higher voltages reduce electrical losses when transporting power to the grid connection point.
Yaw System
For a horizontal axis turbine to operate efficiently, the rotor must face into the wind as much as possible. The yaw system turns the nacelle around the top of the tower so that the rotor points toward the prevailing wind direction.
The nacelle sits on a yaw bearing, a large circular bearing that allows rotation relative to the tower. Yaw drives, which are electric or sometimes hydraulic motors coupled to gears, slowly rotate the nacelle to the desired orientation.
A wind direction sensor, usually a wind vane, is mounted on top of the nacelle. The control system compares the rotor direction with the wind direction and commands the yaw drives to rotate until the rotor is within a small alignment angle. Proper yaw control maximizes power capture and reduces asymmetric loads on the blades and structure.
Pitch System And Braking
Besides yaw, the pitch system is one of the key control components of a turbine. Each blade is mounted on a pitch bearing that allows it to rotate about its axis. Pitch actuators, which can be electric motors with gear drives or hydraulic cylinders, adjust the angle of the blades.
At low and moderate wind speeds, the pitch system fine tunes the blade angle to maximize energy capture. At higher wind speeds, where the turbine reaches its rated power, the blades are pitched to reduce the aerodynamic lift so the power stays at a safe level. In extreme winds or in emergency situations, the blades are pitched to a position that largely removes lift, which slows and stops the rotor. This is known as feathering.
The turbine also has mechanical braking systems. A main mechanical brake is usually installed on the high speed shaft near the gearbox or on the generator shaft. It is often a disc brake similar in principle to those on vehicles, but much larger. The mechanical brake is typically used as a backup or parking brake, for example during maintenance or when the rotor is already nearly stopped by aerodynamic pitching. It is not designed to stop a fast rotating rotor alone, because the loads and temperatures would be too high.
Safe stopping of a wind turbine relies primarily on aerodynamic braking using blade pitch, with the mechanical brake as a secondary or parking system.
There are also fail safe features. For example, many pitch systems are designed so that in case of power loss, springs or hydraulic accumulators move the blades to a safe feathered position automatically.
Control, Sensors, And Safety Systems
Modern wind turbines are highly automated. A central control system monitors and manages all main components. It receives data from many sensors: wind speed and direction sensors on the nacelle, rotor speed sensors, shaft torque sensors, temperatures in gearbox and generator, oil levels, vibrations in tower and nacelle, and grid voltage and frequency.
With this information, the control system performs several tasks. It decides when to start and stop the turbine, controls yaw and pitch to optimize performance, regulates generator torque, and ensures that all components operate within safe temperature and load limits. It also communicates with the wind farm control center or grid operator.
Safety systems are tightly integrated into the control design. If sensors detect conditions outside safe limits, such as very high wind speeds, excessive vibration, or grid faults, the turbine is automatically shut down. The shutdown sequence typically involves pitching blades to a safe angle, activating brakes, disconnecting from the grid, and placing systems in a stable state. Additional safety devices include overspeed protection, lightning protection systems on blades and nacelle, fire detection and suppression in the nacelle, and emergency stop buttons at various locations.
Access, Auxiliary Systems, And Monitoring
For installation, inspection, and repair, technicians must access various parts of the turbine. Inside the tower there are ladders, service lifts or elevators, platforms, and sometimes internal lighting and climate control. The nacelle also has walkways and hatches, and in some designs, external platforms near the hub for blade inspection.
Auxiliary systems support reliable operation. Cooling systems remove heat from the generator, power electronics, and gearbox. These can be air or liquid cooled. Heating systems may be used in cold climates to keep components within acceptable temperature ranges and to prevent condensation. In some regions with icing risk, blade heating or anti icing coatings may be installed to reduce ice build up, which can affect performance and safety.
Finally, a supervisory control and data acquisition, or SCADA, system records operating data, alarms, and events. This remote monitoring system allows operators to track performance, schedule maintenance, and diagnose issues without being physically present at the turbine. It is a key part of managing fleets of turbines safely and efficiently.
Summary
The components of a wind turbine work together as a coordinated system that captures wind energy and delivers usable electricity. Structurally, the foundation, tower, and nacelle provide support and protection. Aerodynamically, the rotor blades and hub interact with the wind. Mechanically, the shaft, bearings, and gearbox transmit torque. Electrically, the generator, power electronics, cables, and transformer condition and transport power. Yaw and pitch systems align the turbine and control loads and power, while control, sensors, and safety systems keep the entire machine operating within safe and efficient limits. Understanding the role of each component lays the groundwork for analyzing turbine performance, design choices, and operational strategies in further chapters.