Rotational Speed of the 22 MW

[lucpavonese]

Hello!

When reading the report of the IEA 22 MW I could see that the rotor speed at lower wind speeds is significantly lower than other turbine models I have seen. Is there any specific reason for the rotor speed of the IEA 22 MW starts rotating at such a lower speed and have this different behavior in comparison with other older turbine models?

Thanks!

[gbarter]

The max tip speed is roughly the same between the different turbine models (not exact, but similar ballpark), but the blade length grows quite a bit. To respect the max tip speed constraint, the rotor rpm must drop. Max tip speed constraint is needed for noise and limiting leading edge erosion among other factors.

[lucpavonese]

Thanks Garrett! I checked the TSR considering the operation points in the excel sheets available for each model and despite observing something similar for the 10 and 15 MW, the behaviour of the 22 MW is still a bit different.

For example, I can see that the TSR is maintained constant up to rated, which is probably the reason behind this linear ramp up in the rotor speed of the turbine until it reaches the rated wind speed (differently than the 10&15 MW, which keeps a constant value rpm for a while the TSR decreases exponentially). Any specific reason for maintaining a constant TSR for the IEA 22 MW? What really calls my attention is this very low starting rotational speed (starting from 1.84 rpm), way lower than the other models, if for example, the IEA 22 MW kept a similar TSR curve as the 15 MW, it would still have margin for increasing the starting rotational speed. Perhaps it was done this way to avoid any tower excitation by the 3P frequency?

Thanks!

[gbarter]

Both the 10-MW and 15-MW reference turbines have a minimum rpm value, a "Region I.5", which is what you are seeing near the cut-in wind speed. A minimum rpm does help with natural frequency management in the system, but on the flip side it requires pitch actuation at low wind speeds which adds to wear and tear. What you are seeing across the reference turbines is a reflection of the multiple design and operational practices in the industry too.

[lucpavonese]

Perfect. Thanks for the explanation!