This work presents a study of the efficiency of 5 fully formulated ISO VG 320 wind turbine gear oils with different bases, a mineral base, a mineral mixed with polyalkylmethacrylate (PAMA) base, a PAO base, an ester base and a polyalkyilene-glicol base (PAG). The main sources of power loss in wind turbine gearboxes are the rolling bearings and gears and these two components were the main focus of this work. To evaluate the behaviour of the selected lubricants efficiency tests were performed with a single thrust ball/roller bearing and also with a complete gearbox. The friction torque in cylindrical roller thrust bearings and thrust ball bearings were measured for a wide range of operating conditions, with contact pressures up to 2.5 GPa and rolling speeds up to 3 m/s. The tests were performed with oil bath lubrication at a constant temperature of 80°C. These tests allowed to compare the lubricants behaviour and to observe the evolution of the friction torque with speed for different loads. The lubricants were also tested for efficiency in a transmission tests rig using a multiplier gearbox with two helical stages and a transmission ratio of 2.3. The lubricants were tested with special focus on the low speed and high torque regimes. Oil bath lubrication was also used in these tests, but the lubricant temperature was set free. The lubricant, gearbox external case and room temperature were used for efficiency evaluation of the tested lubricants. The gearbox test results showed that for the range of operating conditions used the lubricant with best behaviour could promote a decrease in the operating temperature up to 20°C. Numerical models were also implemented for the bearings as well as for the gearbox. The numerical model of the gearbox showed that the Reynolds transition number for the determination of the churning losses needs to be modified and this is clearly observable on the experimental results.
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