The oil viscosity specification for wind turbine gear oils is ISO VG 320, although there are quite different viscosity indexes oils for that viscosity specification. This work evaluates the behaviour of different base oil formulations, since polyalphaolefin (PAO), mineral, ester and polyalkeleneglycol (PAG) that withstand quite different viscosity indexes. The oils evaluation was done in rolling bearing tests and gear tests. Their behaviour was compared for operating conditions in the range observable in a wind turbine gearbox.

The experimental results showed considerable differences between the different oils and it was observed that depending on the contact type the relative behaviour of the lubricants would change, i.e., the best lubricant for the rolling bearing would not imply the best result on the gear tests.

The gear geometry is also very important toward the transmission efficiency, once using a low loss gear concept a decrease of up to 25% in torque loss could be achieved.

Numerical models were implemented with the purpose of performing a better simulation of the mechanical system and also to obtain the friction coefficient promoted by the tested oils.