Power Regulation
Limitation of the power output in high winds is necessary
Limitation of the power output in high winds is necessary on all wind turbines, otherwise the turbine will be overloaded.
Siemens offers two types of power limitation, stall regulation and pitch regulation. Both methods are based on the continuous adjustment of the pitch setting of the blades relative to the hub. Each blade has its own hydraulic actuator unit with position feedback, ensuring continuous stable operation.
- CombiStall®
CombiStall® regulation is used on constant-speed turbines (SWT-1.3-62 and SWT-2.3-82). In low and medium wind speeds, the blade pitch setting is slowly adjusted to provide maximum power output at any given wind speed. When the rated wind speed is reached, the blades are adjusted to a more negative pitch setting, tripping aerodynamic stall and thereby spilling excess power. At higher wind speeds, the pitch angle is adjusted continuously to maintain the maximum power specified.
The advantage of CombiStall® regulation is that it is very simple and efficient, working well with constant speed operation. The disadvantages are that the noise level and blade deflection in high wind are somewhat higher than with CombiPitch regulation. These disadvantages are of little importance for smaller turbines, but for very large turbines, they tend to outweigh the benefits of the robust constant-speed operation.
- CombiPitch
CombiPitch regulation is used on variable-speed turbines (SWT-2.3-82 VS, SWT-2.3-93 and SWT-3.6-107). In low and medium wind speeds the blade pitch setting is slowly adjusted to provide maximum power output at any given wind speed. When the rated wind speed is reached, the blades are adjusted to a more positive pitch setting, thereby reducing the aerodynamic forces and maintaining the power level programmed in to the turbine controller. At higher wind speeds, the pitch angle is adjusted continuously to maintain the maximum power specified.
The advantage of CombiPitch regulation is that it provides low aerodynamic noise and moderate blade deflections. Furthermore, even lower noise can be obtained by special operation. The disadvantage is that variable speed operation is required to provide the necessary flexibility in regulation. However, this disadvantage is of little importance for large turbines, where the benefits of CombiPitch regulation clearly outweigh the added complexity of variable speed operation.