Investigation of Various Condition Monitoring Techniques Based on A Damaged Gearbox Shawn Sheng Senior Engineer, NREL/NWTC 2011 Wind Turbine Condition Monitoring Workshop September 19-21, 2011 Broomfield, CO NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Outline Background Gearbox Reliability Collaborative (GRC) Condition monitoring under the GRC Drivetrain Condition Monitoring Objectives Approach and rationale Implementation Tests Results Observations 2
Gearbox Reliability Collaborative (GRC) Wind turbine gearboxes fail to meet 20 year design life Premature failure of gearboxes increases cost of energy Turbine downtime Unplanned maintenance Gearbox replacement and rebuild Increased warranty reserves The problem Is widespread Affects most OEMs Appears not caused by manufacturing practices Source: Wind Stats 2003 2009 aggregated downtime by turbine subsystem 3
GRC Objectives Facilitate dialog among all parties Understand gearbox response to specific loading Evaluate and validate wind turbine gearbox design practices and modeling & analysis tools, develop or recommend new if needed Establish a database of gearbox failures Investigate condition monitoring methods to increase turbine uptime 4
Condition Monitoring under the GRC One main deliverable from the GRC: improved gearbox design and modeling practices Helps the industry as a whole Provides no information on individual turbine health condition Health Monitoring Helps provide individual turbine health information and increase turbine uptime Condition monitoring (CM) for drivetrain (gearbox, generator, and main bearing) and structural health monitoring (SHM) for rotor 5
Drivetrain CM: Approach and Rationale Integrated Approach Acoustic emission (specifically, stress wave) Vibration analysis Oil debris and condition-monitoring techniques Electric signature-based technique Rationale Each technique has its own strengths and limitations Combine active machine wear detection capability of lubrication oil monitoring techniques with crack location pinpointing capability of acoustic emission and vibration analysis Investigate potential technique for direct-drive turbines 6
Drivetrain CM: Implementation As a research project, this set up is beyond the typical drivetrain CM configuration seen in the industry. 7
Drivetrain CM: Implementation (Cont.) NREL 2.5 MW Dynamometer/PIX16913 8
Tests: Test Articles Two gearboxes rated at 750 kw One planet stage and two parallel stages Redesign Floating sun, cylindrical roller planet bearings, tapered roller bearings in parallel stages, pressurized lubrication, offline filtration and desiccant breather Up to 150 channels of measurements for loads, displacements, and temperature 9
Tests: Conducted Tests Dynamometer test of GRC gearbox #1: run-in Field test of GRC gearbox #1 Dynamometer test of GRC gearbox #2: run-in, nontorque and dynamic torque loading Retest of GRC gearbox #1 in the dynamometer NREL 2.5 MW Dynamometer/PIX16913 10
Tests: GRC Gearbox #1 1. Completed dynamometer run-in test 2. Sent for field test 3. Experienced two oil losses in field test 4. Stopped field test 5. Retested in the dynamometer under controlled conditions High-Speed Stage High-Speed Shaft Pinion Annulus Intermediate-Speed Shaft Planet Carrier Planet Gear Pinion Low-Speed Shaft Sun Gear High-Speed Stage Gear, PIX #19599 Low-Speed Stage Intermediate-Speed Stage 11
Tests: Lubrication System Diagram 12
Results: Stress Wave Amplitude Histogram Parallel stages sensor Healthy GRC gearbox #2 dynamometer test (left) indicated healthy gearbox behavior Dynamometer retest of damaged GRC gearbox #1 (right) indicated abnormal gearbox behavior 13
Results: Vibration Analysis Intermediate speed shaft sensor Healthy GRC gearbox #2 dynamometer test (left) indicated healthy gearbox behavior Dynamometer retest of damaged GRC gearbox #1 (right) indicated abnormal gearbox behavior More sideband frequencies Elevated gear meshing frequency amplitudes 14
Results: Oil Debris Monitoring 800 700 600 500 Particle Counts 400 300 200 100 0 9/15 9/16 9/17 9/18 Date Particle generation rates: Damaged GRC gearbox #1: 70 particles/hour on 9/16 Healthy GRC gearbox #2: 11 particles over a period of 4 hours 15
Results: Oil Sample Analysis Scanning Electron Microscope analysis of a filter cloth used when draining oil from gearbox #1 during disassembly Results: [1] Major particulate constituents in the specimen are steel, iron oxide, brass, and zinc. Likely coming from gears and bearings. Particles by Classification 16
Observations Stress wave amplitude histogram appears effective for detecting gearbox abnormal health conditions. Spectrum analysis of vibration signal (or stress waves) can, to a certain extent, pinpoint the location of damaged gearbox components. Oil debris monitoring, specifically particle counts, is effective for monitoring gearbox component damage, but is not effective for damage location. Damaged gearbox releases particles at increased rates. Oil sample analysis may help pinpoint failed components. Electric signature-based technique did not reveal any gearbox damage in this study. 17
References 1.Herguth Laboratories, Inc. Scanning Electron Microscope Analysis, Herguth Lab #V1093815, February 1, 2011. 2.Sheng, S. and Veers, P. Wind Turbine Drivetrain Condition Monitoring An Overview, Machinery Failure Prevention Technology (MFPT) Society 2011 Conference Proceedings, Virginia Beach, VA, USA, May 10-12, 2011. 3.Sheng, S. (2010). Investigation of Oil Conditioning and Monitoring Techniques for Wind Turbine Gearboxes. The Society of Tribologists and Lubrication Engineers (STLE) 65th Annual Meeting and Exhibition. Las Vegas, NV, USA, May 16-20, 2010. 18
Thanks for Your Attention! Special thanks go to GRC CM partners: CC Jensen, Castrol, Eaton, GasTOPS, Kittiwake, Herguth Laboratories, Lubrizol, Macom, SKF, SKF Baker Instruments, and SwanTech! NREL s contributions to this presentation were funded by the Wind and Water Power Program, Office of Energy Efficiency and Renewable Energy of the U.S. Department of Energy under contract No. DE AC02 05CH11231. The authors are solely responsible for any omissions or errors contained herein. 19
Questions? HC Sorensen, Middelgrunden Wind Turbine Cooperative/PIX17855 shuangwen.sheng@nrel.gov 303 384 7106 20