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DOE OSTI2017

Gearbox Reliability Collaborative Gearbox 3 Planet Bearing Calibration

The Gearbox Reliability Collaborative gearbox was redesigned to improve its load-sharing characteristics and predicted fatigue life. The most important aspect of the redesign was to replace the cylindrical roller bearings with preloaded tapered roller bearings in the planetary section. Similar to previous work, the strain gages installed on the planet tapered roller bearings were calibrated in a load frame. This report describes the calibration tests and provides the factors necessary to convert the measured units from dynamometer testing to bearing loads, suitable for comparison to engineering models.

17 WIND ENERGY↗
DOE OSTI2016

Gearbox Reliability Collaborative Phase 3 Gearbox 3 Test Plan

This document describes the Phase 3 test plan for the Gearbox Reliability Collaborative Gearbox #3. The primary test objective is to measure the planetary load sharing characteristics in the same conditions as the original gearbox design. If the measured load-sharing characteristics are close to the design model, the projected three-times improvement in planetary section predicted fatigue life and the efficacy of preloaded tapered roller bearings in mitigating the planetary bearing fatigue failure mode will have been demonstrated.

17 WIND ENERGY↗
DOE OSTI2015

Gearbox Reliability Collaborative Phase 3 Gearbox 2 Test Report

Many gearboxes in wind turbines have not been achieving their expected design life [1]; they do, however, commonly meet or exceed the design criteria specified in current standards in the gear, bearing, and wind turbine industry as well as third-party certification criteria. The cost of gearbox replacements and rebuilds, as well as the downtime associated with these failures, has elevated the cost of wind energy. In 2006, the U.S. Department of Energy established the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC). Its key goal is to understand the root causes of premature gearbox failures and improve their reliability [2]. The GRC is examining a hypothesis that the gap between design-estimated and actual wind turbine gearbox reliability is caused by underestimation of loads, inaccurate design tools, the absence of critical elements in the design process, or insufficient testing. This test report describes the recent tests of GRC gearbox (GB) 2 in the National Wind Technology Center (NWTC) dynamometer and documents any modifications to the original test plan [3]. In this manner, it serves as a guide for interpreting the publicly released data sets with brief analyses to illustrate the data. Specific objectives of the test were to assess the effect of dynamic nontorque load (NTL) on the planetary section, generator misalignment on the highspeed shaft (HSS), and field representative conditions on the gearbox in general. Detailed analysis of those test objectives will be presented in subsequent publications.

17 WIND ENERGY↗
DOE OSTI2016

Gearbox Reliability Collaborative Phase 3 Gearbox 2 Test

The National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC) was established by the U.S. Department of Energy in 2006; its key goal is to understand the root causes of premature gearbox failures and improve their reliability. The GRC uses a combined gearbox testing, modeling, and analysis approach disseminating data and results to the industry and facilitating improvement of gearbox reliability. This test data describes the tests of GRC gearbox 2 in the National Wind Technology Center dynamometer and documents any modifications to the original test plan. It serves as a guide to interpret the publicly released data sets with brief analyses to illustrate the data. TDMS viewer and Solidworks software required to view data files.

17 WIND ENERGY↗
DOE OSTI2017

Gearbox Reliability Collaborative Phase 3 Gearbox 3 Test Report

Many gearboxes in wind turbines do not achieve their expected design life; they do, however, commonly meet or exceed the design criteria specified in current standards in the gear, bearing, and wind turbine industry as well as third-party certification criteria. The cost of gearbox replacements and rebuilds, as well as the downtime associated with these failures, increases the cost of wind energy. In 2007, the U.S. Department of Energy established the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC). Its goals are to understand the root causes of premature gearbox failures and to improve their reliability. The GRC is examining a hypothesis that the gap between design-estimated and actual wind turbine gearbox reliability is caused by underestimation of loads, inaccurate design tools, the absence of critical elements in the design process, or insufficient testing. This report describes the recently completed tests of GRC Gearbox 3 in the National Wind Technology Center dynamometer and documents any modifications to the original test plan. In this manner, it serves as a guide for interpreting the publicly released data sets with brief analyses to illustrate the data. The primary test objective was to measure the planetary load-sharing characteristics in the same conditions as the original GRC gearbox design. If the measured load-sharing characteristics are close to the design model, the projected improvement in planetary section fatigue life and the efficacy of preloaded TRBs in mitigating the planetary bearing fatigue failure mode will have been demonstrated. Detailed analysis of that test objective will be presented in subsequent publications.

17 WIND ENERGY↗
DOE OSTI2016

Gearbox Reliability Collaborative Phase 3 Gearbox 3 Test

The GRC uses a combined gearbox testing, modeling, and analysis approach disseminating data and results to the industry and facilitating improvement of gearbox reliability. This test data describes the tests of GRC gearbox 3 in the National Wind Technology Center dynamometer and documents any modifications to the original test plan. It serves as a guide to interpret the publicly released data sets with brief analyses to illustrate the data. TDMS viewer and Solidworks software required to view data files. The National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC) was established by the U.S. Department of Energy in 2006; its key goal is to understand the root causes of premature gearbox failures and improve their reliability.

17 WIND ENERGY↗
DOE OSTI2021

Gearbox Reliability Collaborative 1.5 (GRC1.5) Project: Joint Industry Megawatt Scale Gearbox Field Tests: Cooperative Research and Development (Final Report) CRADA Number CRD-16-00608

A new DOE/NREL industry collaboration called the Gearbox Reliability Collaborative 1.5 (GRC1.5) will undertake field testing on a commercial multi-megawatt wind turbine gearbox to collect loading data as installed in the turbine to thoroughly characterize gearbox loads and responses during actual in-field conditions. A chief outcome is to provide publicly available operational loading data to the industry. This will provide a greater understanding of steady-state, transient, and fault response for both the input and output of the gearbox; thus, facilitating improvements in the gearbox components, lubrication system, power converter or turbine controller.

17 WIND ENERGY↗
DOE OSTI2016

Gearbox Reliability Collaborative Investigation of Gearbox Motion and High-Speed-Shaft Loads

This paper extends a model-to-test validation effort to examine the effect of different constant rotor torque and moment conditions and intentional generator misalignment on the gearbox motion and high-speed-shaft loads. Fully validating gearbox motion and high-speed-shaft loads across a range of test conditions is a critical precursor to examining the bearing loads, as the gearbox motion and high-speed-shaft loads are the drivers of these bearing loads.

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DOE OSTI2014

Gearbox Reliability Collaborative High-Speed Shaft Calibration

Instrumentation has been added to the high-speed shaft, pinion, and tapered roller bearing pair of the Gearbox Reliability Collaborative gearbox to measure loads and temperatures. The new shaft bending moment and torque instrumentation was calibrated and the purpose of this document is to describe this calibration process and results, such that the raw shaft bending and torque signals can be converted to the proper engineering units and coordinate system reference for comparison to design loads and simulation model predictions.

17 WIND ENERGY↗
DOE OSTI2016

Gearbox Reliability Collaborative Investigation of High-Speed-Shaft Bearing Loads

The loads and contact stresses in the bearings of the high speed shaft section of the Gearbox Reliability Collaborative gearbox are examined in this paper. The loads were measured though strain gauges installed on the bearing outer races during dynamometer testing of the gearbox. Loads and stresses were also predicted with a simple analytical model and higher-fidelity commercial models. The experimental data compared favorably to each model, and bearing stresses were below thresholds for contact fatigue and axial cracking.

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DOE OSTI2014

High-Speed Shaft Bearing Loads Testing and Modeling in the NREL Gearbox Reliability Collaborative: Preprint

Bearing failures in the high speed output stage of the gearbox are plaguing the wind turbine industry. Accordingly, the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC) has performed an experimental and theoretical investigation of loads within these bearings. The purpose of this paper is to describe the instrumentation, calibrations, data post-processing and initial results from this testing and modeling effort. Measured HSS torque, bending, and bearing loads are related to model predictions. Of additional interest is examining if the shaft measurements can be simply related to bearing load measurements, eliminating the need for invasive modifications of the bearing races for such instrumentation.

17 WIND ENERGY↗
DOE OSTI2024

GRC1.5 Project: Joint Industry Megawatt Scale Gearbox Field Tests (Final Report)

A new DOE/NREL industry collaboration called the Gearbox Reliability Collaborative (GRC) 1.5 will undertake field testing on current commercial multi-megawatt wind turbine gearboxes to collect loading data from installed turbines to thoroughly characterize gearbox input loads and responses during actual in-field conditions. A chief outcome is to provide operational loading data relative to the most common failure modes. This will provide a greater understanding of steady-state, transient, and fault response for both the input and output of the gearbox, thus facilitating improvements in the gearbox, power converter or turbine controller.

17 WIND ENERGY↗
DOE OSTI2017

Planetary Load Sharing in Three-Point- Mounted Wind Turbine Gearboxes: Preprint

Wind turbine gearboxes do not achieve their expected design life. The cost of gearbox replacements and rebuilds and the downtime associated with these failures increase the cost of wind energy. In 2007, the U.S. Department of Energy established the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC). Its goals are to understand the root causes of premature gearbox failures and improve their reliability. To date, the GRC has focused on a 750-kW drivetrain with a three-stage, three-point-mounted gearbox. A nonproprietary version of the gearbox containing CRBs with C3 clearances in the planetary stage was customized. Two of these gearboxes, GB1 and GB2, were manufactured and then tested in the National Wind Technology Center's 2.5-MW dynamometer and in the field. Major GRC findings include the detrimental effect of rotor moments on planetary load sharing and predicted fatigue, and the risk of bearing sliding in low-torque conditions for three-point configuration drivetrains. Based on the knowledge gained from testing and analysis of the original design, the GRC gearbox was redesigned to improve its load-sharing characteristics and predicted fatigue. This new gearbox is named GB3. As shown in Figure 1, its key improvement is the incorporation of preloaded TRBs that support the planet carrier and planets. Roller loads can be optimized and bearing life maximized with a small preload [4]. These preloaded bearings, along with interference-fitted planet pins, improve alignments and load-sharing characteristics. A semi-integrated planet bearing design also increases capacity and eliminates outer race fretting. Romax Technology, with Powertrain Engineers and the Timken Company (Timken), completed the redesign. Timken manufactured and instrumented the planet gears and bearings. Brad Foote Gearing manufactured the other gearing and assembled the gearbox.

17 WIND ENERGY↗
DOE OSTI2015

Experimental Characterization of a Grid-Loss Event on a 2.5-MW Dynamometer Using Advanced Operational Modal Analysis: Preprint

This paper experimentally investigates a worst case grid loss event conducted on the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC) drivetrain mounted on the 2.5MW NREL dynamic nacelle test-rig. The GRC drivetrain has a directly grid-coupled, fixed speed asynchronous generator. The main goal is the assessment of the dynamic content driving this particular assess the dynamic content of the high-speed stage of the GRC gearbox. In addition to external accelerometers, high frequency sampled measurements of strain gauges were used to assess torque fluctuations and bending moments both at the nacelle main shaft and gearbox high-speed shaft (HSS) through the entire duration of the event. Modal analysis was conducted using a polyreference Least Squares Complex Frequency-domain (pLSCF) modal identification estimator. The event driving the torsional resonance was identified. Moreover, the pLSCF estimator identified main drivetrain resonances based on a combination of acceleration and strain measurements. Without external action during the grid-loss event, a mode shape characterized by counter phase rotation of the rotor and generator rotor determined by the drivetrain flexibility and rotor inertias was the main driver of the event. This behavior resulted in significant torque oscillations with large amplitude negative torque periods. Based on tooth strain measurements of the HSS pinion, this work showed that at each zero-crossing, the teeth lost contact and came into contact with the backside flank. In addition, dynamic nontorque loads between the gearbox and generator at the HSS played an important role, as indicated by strain gauge-measurements.

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