The wind turbine generator converts mechanical energy to electrical energy. Wind turbine generators are a bit unusual, compared to other generating units ordinarily found attached to the electrical grid. One reason is that the generator has to work with a power source, the wind turbine rotor, which supplies very fluctuating mechanical power, torque.
These pages assume that you are familiar with the basics of electricity, electromagnetism, induction and in particular alternating current.
On large wind turbines (above 100-150 kW) the voltage generated by the turbine is usually 690 V three-phase alternating current (AC). The current is subsequently sent through a transformer next to the wind turbine, or inside the tower, to raise the voltage to somewhere between 10,000 and 30,000 volts, depending on the standard in the local electrical grid.
Large manufacturers will supply both 50 Hz wind turbine models for the electrical grids in most of the world and 60 Hz models for the electrical grid in America.
Generators need cooling while they work. On most turbines this is accomplished by encapsulating the generator in a duct, using a large fan for air cooling, but a few manufacturers use water cooled generators. Water cooled generators may be built more compactly, which also gives some electrical efficiency advantages, but they require a radiator in the nacelle to get rid of the heat from the liquid cooling system.
Starting and stopping the generator
If you connect or disconnect a large wind turbine generator to the grid by flicking an ordinary switch, you will be quite likely to damage both the generator, the gearbox and the current in the grid in the neighbourhood.More things on how turbine designers deal with this challenge can be found on the page on Power Quality.
Design choices in generators and grid connection
Wind turbines may be designed with either synchronous or asynchronous generators and with various forms of direct or indirect grid connection of the generator. Direct grid connection mean that the generator is connected directly to the (usually 3-phase) alternating current grid. Indirect grid connection means that the current from the turbine passes through a series of electric devices which adjust the current to match that of the grid. With an asynchronous generator this occurs automatically.
- Generator, basic concept: general explanation of electromagnetism