Modern wind turbines generate electricity by using wind to spin their blades. This rotational motion spins a generator, which generates electricity. The following describes wind turbine major components in more detail.
The blades capture the convert the wind energy into rotational energy that can be turned into electricity by the generator. Blades are constructed from materials including wood (core), foam (form), fibreglass and Kevlar.
Wind turbine blades are shaped like aerofoils. Aerodynamically, they are more like an aircraft wing than the angled vanes featuring on old wind mills.
The nacelle is essentially a box containing the generator, gearbox and other auxiliary systems including cooling and lubrication systems.
Wind turbine generators vary in technology. They can be based on induction machines, permanent magnet generators or even synchronous machines. They convert the rotational energy of the blades, via the main shaft to electricity.
Many wind turbines contain a gearbox. Wind turbine gearboxes convert the low rotational speed of the blades into a speed suited to the generator. Wind turbine gearboxes can have conversion ratios of 1:100. This is a unique application. Most (general) gearbox applications require reduction gearboxes. Reduction gearboxes convert high speed/low torque into low speed/high torque. On a wind turbine the application requires conversion of high torque at low speed into high speed. This presents challenges for the gearbox manufacturers. As a result, gearboxes present a high portion of the ongoing cost of wind turbine major component failure costs.
The wind turbine tower is typically a large steel tube. Its height often exceeds 80m. Therefore, the tower must be constructed in sections and joined on site using bolted flanges. The tower contains a ladder and usually a lift, to enable wind turbine technicians to access the nacelle.
Electrical cabling moves electricity from the generator, down the tower and back to the substation. The substation sends the energy to the electrical transmission or distribution system. Typical wind turbine generators operate below 1000V. This voltage is transformed to 22kV or 33kV via a wind turbine transformer. The transformer is either located in the nacelle, or at the bottom of the tower (inside or outside). Increasing the voltage allows efficient and economical transportation of power from the turbine through the wind farm, to the substation.
The blades are connected to pitch bearings and drives which enable the blades to be rotated or pitched. Pitching the blades controls the power output. The blades are angled either to extract the maximum energy from the available wind, or to curtail the power such that the wind turbine’s rated power and design loads are not exceeded.
Pitch systems can be hydraulic or electrical, and rotate with the blades in the spinner (or hub). This presents design challenges bringing power and signals from the stationary nacelle, into the spinning hub. Pitch-related alarms are a common cause of breakdowns on wind turbines.
The yaw system consists of electrical motors and gearboxes that rotate the nacelle upon the tower. This ensures the blades are always facing into the wind. Poor nacelle alignment can result in wind turbine underperformance and asymmetrical stresses across the drivetrain.
Wind Turbine Controller
The wind turbine controller is more like an industrial computer than a PLC. It makes decisions that maximise wind turbine production while keeping the equipment safely within operating limits. It records analogue data from attached sensors and logs alarm and event data. This SCADA data is then sent to a central server to be stored for later analysis.
Bachmann, Mita Teknik and Deif controllers are popular within the wind industry.
Examples of wind turbine controller tasks include:
- Starting the turbine when the wind speed exceeds the minimum level. This is achieved by commanding the blades to pitch to catch the wind
- Regulating the power output by altering the angle of the blades into the wind
- Keeping the turbine pointed directly into the wind by analysing data from a nacelle-mounted wind vane
- Shutting down the turbine if a signal from a temperature sensor indicates a wind turbine component is too hot.
- Sending alarm data to the wind turbine SCADA system to alert wind turbine technicians to a breakdown