I have simulated the 5MW WT with OC3 Hywind Spar (with unchanged settings). I plotted the graph for GenPwr against time and found that at certain time step, it reached more than 5MW (around 5.5MW).
Next I changed the wind inflow file to a PwrCrv.wnd file with wind speed from 5m/s to 25m/s (everything else unchanged) and observed the GenPwr reach 8MW.
How are we supposed to interpret these values? Is it permissible that the GenPwr reaches above 5MW?
I am aware that the cut-in, rated and cut-out wind speed of the NREL 5MW WT is 3m/s, 11.4m/s and 25m/s. Does this have anything to do with the high values perhaps?
I found this post: http://forums.nrel.gov/t/nrel-5mw-controls-dll-interface/183/21
where you explain that the controller will not shut down for wind speeds above cut-out wind speeds (25m/s in this case). But what about a situation when GenPwr is greater than the rated power?
the question might be bit silly, but I couldn’t reason it.
The baseline controller for the OC3-Hywind floating wind system does not include start-up or shut-down logic. And the generator-torque control strategy when operating at rated power (Region 3) employs simple constant generator-torque; that is, if the rotor speed exceeds rated speed, the generator power will exceed rated power. I would only expect this overloading of the generator for short periods of time when the pitch controller is working to regulate the rotor speed back down to rated speed. This is discussed briefly in the OC3-Hywind specifications report (section 6): nrel.gov/docs/fy10osti/47535.pdf.
Dear Dr. Jason,
Thank you for your explanation. The document indeed clears up the doubt for increased GenPwr and using constant torque control strategy in Region 3.
I wanted to know the implications for overloading of the generator even for short span of time.
Does that mean that in practical scenarios, the manufacturer would have to consider such occurences while designing the generator for a specific rated wind turbine?
I’m not an expert in generator design, but yes, I would imagine that brief overloading of the generator would have to be considered in the generator design.