Gearbox efficiency

Hi everybody

I am using FAST for modelling wind turbine. In my model, gearbox efficiency is less than 100%. Then, how can I consider gearbox efficiency in VS_Rgn2K (generator constant in region 2). From documents we know that VS_Rgn2K is calculated in HSS side as below

VS_Rgn2K = 0.5 * (Air_density) * (pi) * (radius^5) * Cp_max/(landa_opt^3) * (1/Ngear)^3 * (pi/30)^2

But how does gearbox efficiency affect VS_Rgn2K?

Thanks a lot

Dear Feizbakhshi,

A gearbox efficiency (GBoxEff) in FAST less than 100% causes the power of the output shaft to be less than the power of the input shaft by the efficiency. That is, HSShftTq = LSShftTqGBoxEff/GBRatio (for positive torque/power generator) or HSShftTq = LSShftTq/(GBoxEffGBRatio) (for negative torque/motoring). So, you’ll have to multiply VS_Rgn2K by GBoxEff (effecting reducing Cp_max) to get the effective HSS generator torque to counteract the aerodynamic torque, accounting for gearbox friction.

Best regards,

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Hi Jason,
in my current model in Fast v8.08, Fast aborts when I use GBoxEff smaller than 100.
“Message from ED_Input: ED_Init:ED_ValidateInput: GBoxEff must be 1 (i.e., 100%)”
Does it depend on my model or is it generally impossible to model gear box losses in Fast 8?
Best regards

Dear Niklas,

We’ve disabled gearbox efficiency losses in FAST v8 because the method used to implement it in FAST v7 was not easily transferrable to FAST v8, which uses different solver/coupling options. We plan to add this feature back in the future, but we have not had the resources yet to do so.

For a complete list of features supported by FAST v7 and v8, please see the ReadMe file distributed with FAST v8:

Best regards,


I am trying to use the option for reading the GBoxEff in ElastoDyn as a table from a separate file. Currently I am using OpenFAST v2.5.0.

Trying different methods and formats I was not able to determin the needed structure for this.

Is there an example as a baseline for this application?

Thanks and best regards,

Dear Simon,

The ElastoDyn module of OpenFAST does not currently support a tabulated form for the gearbox efficiency; instead, GBoxEff must be specified as as single value.

Best regards,