The power generation from wind power plants is different from conventional power plants. This is mainly due to the maverick nature of the wind energy. This requires special controls and different types of electrical generators. For a brief explanation read this article.
In a conventional power plant, the input energy follows the output, the electrical load.
In a wind power plant, the control on the input energy is limited. In addition, you have to make use of what is available and at the same time balance the electrical characteristics. Wind power plants are different for this reason.
The conventional power plant uses a synchronous generator. It runs at a speed dictated by the grid frequency. Precise control of the input energy is possible when the electrical load on the generator changes. This effectively controls the speed to match with the grid frequency.
In a wind turbine generator, control of the input energy, which is torque from the rotation of the wind turbine, is not that easy. The input energy with the wind speeds vary in a wide range. Most of the manufacturers limit wind speeds within a range of 4 m/s to 25 m/s. There can also be sudden gusts of wind. The generator on the other hand tries to rotate at a speed near to synchronous speed dictated by the grid frequency. The generator is subject to undue stress due to this contrasting effect. The normal synchronous generator cannot respond to these sudden changes. To overcome these problems different types of electric generators are made use of in a wind power plant.
The most commonly used is the asynchronous generator and the variable frequency method.
A certain amount of mechanical control is available in the wind turbine blades to control the speed.
What happens when the wind speed increases beyond the maximum power output capacity of the generator?
- In pitch controlled wind turbines, a twist to the individual blades prevent transmission of the full force of the wind to the generator. This is like changing the direction of the sail in a sailboat. This type of wind turbine requires an electrically or hydraulically operated pitch control mechanism.
- In stall controlled wind turbines, the shape of the blades create aerodynamic forces that reduce the torque output of the turbines at higher wind speeds.
- When the direction of the wind changes, anemometers sense these changes and operate the “yaw “mechanism which turns the turbine to face the wind.
- When the wind speeds are beyond the range of these controls, the turbine rotation stops by the use of mechanical or hydraulic brakes.
The electrical system provides further controls.