Correlation of Planetary Bearing Outer Ring Creep and Gear Load Distribution in a Full-Size Wind Turbine

Abstract

In this work, bearing outer ring creep in the planetary gear of a gear wind turbine gearbox is investigated. So far, gear creep has only been investigated experimentally on very small bearings under simplified load conditions. This paper presents experimental measurement results from a full-size 2.75 MW wind turbine. The test were performed on a system test bench capable of applying loads in all six degrees of freedom at the rotor hub. The objectives of this investigation are to provoke and measure bearing outer ring creep and to identify correlations to the gear load distributions acting on the planetary gear. After a motivation, a literature overview on bearing ring creep is given. Influences on and occurrences of ring creep are described and the two mechanisms roller-induced creep and gear creep explained. Then, the test setup and the evaluated experiments are presented. The influence of torque, rotational speed and additional non-torque loads on gear load distribution and bearing outer ring creep is shown, discussed and put in relation to findings from literature. Key findings are that outer ring creep speed increases with global rotational speed and torque. Also, gear creep – acting in the opposite direction of roller-induced creep – was found at the generator-sided bearing ring for loads below 40% nominal torque. The planet gear load distributions with sun and ring gear were highly uneven and opposed to each other at low torques while leveling out at high torques due to the load-dependent deformations of sun gear, planet carrier and ring gear. The average gear load distribution over all ring gear positions showed to be influenced only by torque and to be independent of non-torque loads. In accordance, even extreme non-torque loads were found to not influence the creep behavior of the two planetary bearing outer rings.