Exploring Limiting Factors of Wear in Pitch Bearings of Wind Turbines with Real Scale Tests

Abstract

Abstract. Oscillating movements under load can cause wear in rolling bearings. Blade bearings of wind turbines are subject to both. To know how to avoid wear in these bearings is important since they ensure the operational safety of the turbine. Oscillations of blade bearings vary in load, speed, and amplitude. The objective of this work is to find limits of these operating parameters with regards to wear occurrence. To this end several tests with real size bearings were carried out. The test parameters are based on typical operating conditions of a reference turbine. The size of the bearings and the test parameters differ from other published test results for oscillating bearings. The test results show that wear occurs for every tested combination of load, speed, and amplitude of a steady oscillating movement. Even if the wear characteristics differ between tests, each of them resulted in wear. Hence, no wear limits can be defined within typical operating conditions of a wind turbine below which wear does not occur. Tests with a discontinuity in the steady oscillation movement, however, did not result in wear. Such discontinuities can be longer movements embedded in steady oscillations. They are characteristic to wind turbine operation, where longer movements are a reaction to wind gusts.

Wear Development in Oscillating Rolling Element Bearings

“…BEHNKE ET AL. also show results of wear tests of real size blade bearings with the same grease as lubricant [5]. Especially for the smaller amplitude ratios wear already occurred for only 1 000 cycles, which matches the fast wear initiation obtained in the tests with the type 7220 bearings in this paper.…”

“…and WANDEL ET AL. found, that the very small oscillation movements are most likely not the most critical ones when it comes to wear as a failure mode and the middle range of amplitude ratios has a greater impact [5,6] . However, the stochastic nature of the wind and operating conditions of the wind turbine as well as the influence of the specific order of occurrence of cyclic movements of the blade bearings makes rating the risk of wear damage a very difficult topic.…”

“…This method is usually called individual pitch control (IPC). Recent investigations showed that IPC in contrast to CPC can decrease the number of very small oscillation movements and leads to generally larger oscillation amplitudes [4,5]. These oscillation angles depend on the individual controller and turbine design and do not allow for a general statement.…”

Research on the crack behaviors under rolling contact of oscillation applications in wind turbine bearings

“…They pointed out that the bearing in an oscillation condition behaves differently from that in rotating, and the oscillation factor aosc was introduced to consider the difference. Both [6] and [7] indicated that the sequence and amplitude of an oscillation movement play an important role in wear occurrence.…”

Review of rolling contact fatigue life calculation for oscillating bearings and recommendations for use, with examples for wind turbine bearings

“…Rolling bearings under oscillatory movements are commonly associated with wear damage to the raceways and rolling bodies (Behnke and Schleich, 2022;Stammler, 2020;Grebe, 2017;FVA, 2022;de La Presilla et al, 2023). In some cases, such as large amplitudes, varying amplitudes, or the use of oil lubrication, wear is unlikely to occur and rolling contact fatigue becomes more relevant.…”