Mainshaft Bearings: Bearing Arrangements, Damage Modes and Technology Advancements Presented by Richard Brooks AWEA O&M Conference 2017 1
BEARING TYPE COMPARISON Spherical Roller Bearing Radial Internal Clearance (RIC) Line Contact (mostly) +Radial Load + Thrust Load <25% + Misalignment ++Misalignment Cylindrical Roller Bearing Radial Internal Clearance (RIC) Line Contact o +Radial Load o - Thrust Load (<10%) o -- Misalignment Tapered Roller Bearing Can be Pre- Loaded Line Contact o +Radial Load o ++ Thrust Load o - Misalignment o (100%+) o +Misalignment SRB CRB TRB 2
MAIN BEARING ARRANGEMENTS MODULAR TURBINES 3-Point Mount 4-Point Mount Direct Mount Single Bearing Two Bearings Single Bearing Single SRB Gearbox Torque arm supports 2 SRBs, 2 TRBs, or TRB + CRB Gearbox Torque arm supports Single TRB Gearbox directly mounted to rotor and frame 3
3-POINT MOUNT MODULAR Single SRB Single Spherical Roller Bearing mounted in a pillow block supporting the main shaft. Used to accommodate misalignment, radial load, and axial load. Advantages Less nacelle mass Lower cost Accommodates misalignment Disadvantages Multiple bearing damage modes Allows excessive thrust into the gearbox Examples: GE 1.X, Siemens 2.3MW, Suzlon S88, Mitsubishi 1MW, Vestas V82 4
3 POINT : SRB OBSERVED DAMAGE Micropitting Edge Loading Cage Damage Debris Damage Pictures are illustrative and not necessarily from this mounting configuration 5
4-POINT MOUNT MODULAR Two SRBs TRB and CRB Two TRBs Two Bearings mounted in separate pillow blocks supporting a main shaft. Different series bearings used for radial and axial loads, reducing misalignment. Advantages Less misalignment Lower bearing failure rates Less thrust into gearbox Disadvantages Higher mass Higher cost TRBs sensitive to setting SRB not ideal for high thrust loads Examples: Vestas V80, Gamesa G87, Acciona 1500, GE 2.5MW, Vestas V164 6
4 POINT : DOWNWIND SRB OBSERVED DAMAGE Cage Damage Debris Damage 4 POINT : TRB OBSERVED DAMAGE Improper Preload White Etch Cracks (rare) Pictures are illustrative and not necessarily from this mounting configuration 7
FAILURE STATISTICS 3 Point Mount 4 Point Mount Main bearing: 0.5%/year Gearbox: 5.9%/year Main bearing: 0.2%/year Gearbox: 0.8%/year 3 Point mount has 250% higher main bearing failure rate and 637% higher gearbox failure rate! Data Source: DNV GL, Major Component Failure Data & Trends, Bill Berger, 2016. 8
FLEET DATA -SRBS 50.00% Main Bearing Failure Rates 45.00% 40.00% 35.00% 30.00% Most 3 point SRBs are failing prematurely, but rate vary by turbine & bearing series. Failure Rate 25.00% 20.00% 15.00% 10.00% 5.00% 0.00% 5.00% 0 2 4 6 8 10 12 14 Site Age in Years SE 2.3 (230) GE 1.5 (230) GE 1.5 (240) V72 (230) V80 (241) 3 pt (230) 3 pt (230) 3 pt (240) 3 pt (230) 4 pt (240/241) 9
DIRECT MOUNT MODULAR TRB Advantages No main shaft, less nacelle mass Rigid system to absorb thrust and handle overturning moments Examples: Vestas V90 3MW, Mitsubishi 2.4 A large diameter, high contact angle double row Tapered Roller Bearing integrated into the gearbox. It is directly mounted to the rotor hub on a stub shaft without a long main shaft. Main bearing also functions as the carrier bearing. It is preloaded to handle radial, axial, and moment loads. Disadvantages Requires a large precision TRB with steep contact angles Main bearing cannot be replaced without replacing the gearbox 10
DIRECT MOUNT: MAIN SHAFT TRB OBSERVED DAMAGE Damage from loss of Pre-Load Typically caused by assembly Cage damage Often design / material related Pictures are illustrative and not necessarily from this mounting configuration 11
SOLUTIONS: MAIN SHAFT SRB #1: ENHANCEMENTS TECHNOLOGY DESCRIPTION BENEFITS Roller Finishing Roller Coating Low Roughness, Enhanced Finish DLC Coating ~1 µm thick Reduced Asperity Contact & Stress Increased Wear Resistance Increased Fatigue Life Increased Debris Resistance Internal Geometry Roller/IR Conformity Decreases Roller Stress, Reduces Potential Roller Skew Creates Favorable Traction Split Cage Two-Piece Machined Brass Cage with no Guide Ring Lowers Possible Operating Forces Removes source of debris generation Texturing Coating 12
SOLUTIONS: MAIN SHAFT SRB #2: RE-DESIGN REPLACE WITH TRB Spherical Roller Bearing (SRB) Internal clearance Limited thrust capability Helpful with misalignment Not true rolling motion Tapered Roller Bearing (TDI) Preloaded for rigidity High thrust and radial capacity Must control misalignment True rolling motion An observed reduction of axial thrust into gearbox by 67% will decrease stress. This can increase bearing and gearbox life. 13
MAIN SHAFT SRB PREVENTION Susceptible to inherent design flaw of high slip causing premature catastrophic damage Particularly evident on 3 point mounting Lubrication: Follow or exceed OE recommended quantities and frequency Consider a purge or flush after several years based on condition DETECTION Temperature trend looking for park outliers Grease sampling for Iron content Vibration (may require special algorithms) spj9 14
Slide 14 spj9 Was "3 point failures cannot be fully prevented. Inherent to the design" johnsost, 2/23/2017
MAIN SHAFT TRB & CRB PREVENTION Proper bearing design (surface finish, roller mass, preload/clearance) to prevent micropitting Lubrication: Carefully Follow OE recommended quantities and frequency DETECTION Temperature trend looking for park outliers Monitor grease condition sample for Iron and other debris content Check bolt tension some models Vibration (may require special algorithms) 15
MAIN SHAFT -TAPERED ROLLER BEARINGS IN DIRECT DRIVE Narrow Mount Spread Mount Single 2 row TRB 2 TRBs, or TRB + CRB 16
NARROW MOUNT DIRECT DRIVE A large diameter, high contact angle double row Tapered Roller Bearing mounted to the rotor. It is preloaded to handle radial, axial, and moment loads. TRB Advantages Reduced axial space no main shaft Single bearing supports blade loads Factory pre-set Low risk of sliding High stiffness Flexible mounting/sealing designs Examples: Siemens 3MW, Goldwind 2.5MW Disadvantages Sensitive to bearing setting High bearing mass Custom bearing design 17
SPREAD MOUNT DIRECT DRIVE Two wide spread bearings mounted on a main shaft. TRB and CRB Two TRBs Advantages Pre-set (TRB and CRB) Lower mass Adaptable for most turbine sizes Classical arrangements used in gearboxes Disadvantages May require wind turbine builder to set the bearings (2 TRB) Requires long main shaft Potential sliding risk for CRB and larger rollers Examples: Goldwind 1,5MW, Enercon, WEG 18
DIRECT MOUNT: MAIN SHAFT TRB OBSERVED DAMAGE Damage from loss of Pre-Load Typically caused by assembly White Etch Area Cracks Rare Cage damage Often design / material related Pictures are illustrative and not necessarily from this mounting configuration 19
MAIN SHAFT, DIRECT DRIVE TRBS PREVENTION Proper mounting design validate with FEA Maintain proper bolt tension some models Lubrication: Follow OE recommended quantities and frequency DETECTION Temperature trend looking for park outliers Monitor grease condition sample for Iron and other debris content Check bolt tension some models Vibration (Challenging due to generator interference) 20
SUMMARY Damage Modes in Main Shaft Bearings Well Understood SRBs Accommodates Misalignment Have the highest observed failure rates 3-point mounts much higher failure rate than 4-point mounts TRBs A precision arrangement Becoming more common in larger turbines & Direct Drive Better system performance but more sensitive to assembly tolerances 21
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