Dear Ana,
For clarification of how the drivetrain model in FAST works, please see the following forum post: Resistant moment of the rotor and of the electric generator. Please note that following nomenclature differneces between that post and your post:
Your Post → Linked Post
GenTq → T_Gen
RotTorq → LSShftTq
RotPwr → LSShftTqRotSpeed
HSShftPwr → HSShftTqGenSpeed
To clarify, the electrical torque (GenTq = T_Gen) is the torque applied to the generator rotor (or high-speed shaft (HSS)) from the generator stator. This should equal the mechnical torque within the HSS, HSShftTq, if the HSS is not accelerating or decelerating. It is the generator electrical power, GenPwr, that is influenced by the generator efficiency – see point 3 in the post linked above. Also, GenModel is only used when VSContrl = 0.
I hope that helps.
Best regards,