# Mass and inertias for 20 mw wind turbine

Hi @Garrett.Barter and @Jason.Jonkman , i have questions regarding the mass and inertia parameters from the 15 MW wind turbine ElastoDyn file:

1º How can be “the moment of inertia for the hub mass around x-axis that goes through the center of mass” be calculated? For the 15 MW wind turbine, it is 973520 kg*m^2 but i do not know where this comes from.

2º In order to know HubIner (Hub inertia about rotor axis ) and NacYIner (Nacelle inertia about yaw axis) for a 20 MW WT, How could it be done.? I read in the Turaj Ashuri PhD thesis that Mass inertias scales up with a R^5 ratio, but i want to make it sure.

3º Regarding GenIner (Generator inertia about HSS), i did not find any piece of information about the generator inertia in this paper (https://www.sciencedirect.com/science/article/pii/S0306261923006360). How could the generator inertia be known?

4º How would PtfmYIner (Platform inertia for yaw rotation about the platform CM (kg m^2)) scale from the 15 MW wind turbine to 20 MW?

5ºHow would the DTTorSpr(Drivetrain torsional spring) and DTTorDmp (Drivetrain torsional damper) scale from the 15 MW IEA Wind turbine to the 20 MW?

Thank you very much

Much of the mass properties for the 15-MW turbine in the OpenFAST ElastoDyn file were computed by WISDEM. In answer to your questions:

1. This was computed by WISDEM by adding up the moment of inertia contributions from the hub system components (spherical shell, pitch systems, etc.). You can trace the calculation starting here.
2. I’m not quite sure I follow all the details, but from your prior questions, I’m assuming that your comment of scaling by “R^5” is referring to rotor diameter or blade length? That sounds more like an empirical fit than a rule of physics. Our published designs are point designs, meaning we tried to avoid scaling rules and curve fits for the major components.
3. That paper did detailed generator designs and had estimates for generator rotor and generator stator mass values. However, we couldn’t go so far as to do a CAD-based calculation of moments of inertia because we did not perform detailed design of the cooling or secondary electronics subsystems. Instead, we simply considered the generator a cylindrical mass and computer generator inertias using this approach in WISDEM.
4. Again, we try to avoid scaling rules and did point designs in our work. I do not have an easy answer for you here. The best starting point for you might be the recently released IEA Wind 22-MW reference turbine.

I am so grateful for this help @Garrett.Barter

Hi @Garrett.Barter, @Daniel.Zalkind ,
Please how is the ROSCO parameter “WE_Jtot - Total drivetrain inertia, including blades, hub and casted generator inertia to LSS” computed? Can it be computed directly from OpenFAST inputs? Looking forward to your response.
BR
Salem

Hi Salem,

The value for `WE_Jtot` is calculated here: ROSCO/rosco/toolbox/turbine.py at a4a6a271eb4c422b1d2b3c4a8f68fbc80b52fc46 · NREL/ROSCO · GitHub

The ElastoDyn summary output provides the rotor inertia and the generator inertia is an ElastoDyn input.

Best, Dan

Thanks very much.
Best, Salem