roller sliding in wind turbine gearbox hss bearings · 2019. 5. 8. · roller sliding in wind...
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Roller Sliding in Wind Turbine Gearbox High-Speed-Shaft Bearings
4th Conference for Wind Power Drives 2019, Aachen, March 13, 2019
David Vaes, SKFJon Keller, National Renewable Energy LaboratoryPietro Tesini, SKFYi Guo, National Renewable Energy Laboratory
Photo by Jonathan Keller, NREL 49037
NREL/PR-5000-73428
© SKF Group
• Background
• Measurement setup
• Numerical model building and verification
• Transient load conditions
• Conclusions
Overview
Background
Photo from SKF
© SKF Group
Background: Premature Failures with White Etching CracksHS-S
HIS-SLS-P
• During recent years several countermeasures have been taken
• Since introduction of black-oxidising, no serial failure case reported by gearbox original equipment manufacturer
• Some failures still reported today by after market and end users:– Proper statistics are
missing.
Early cracks occur commonly within the
first 1–3 years of operational time
(<10% of the calculated rating life).
Photos from SKF
LS-P = Low-Speed PlanetHS-S = High-Speed ShaftHIS-S = High Intermediate-Speed Shaft
Illustration from SKF
© SKF Group
Premature Bearing Failures: Understanding the Drivers
‘Cyclic’ Stressesand Loading
Rolling Contact Fatigue
‘Accelerated’ Fatigue (Premature Spalling)
Higher ‘Stresses’ Lower ‘Material Strength’
WEC in bearing test exposed to additional
tensile stresses.
WEC in bearing test exposed to short heavy
loads.
White Etching Cracks (WECs) Occurrence in Bearings
Structural Stresses(Sub-Surface)
Frictional Stresses and Wear(Surface, Near-Surface)
Hydrogen(Surface and Sub-Surface)
WEC in larger bearing rolling contact fatigue.
WEC in bearing test exposed to water stand-
still corrosion.
WEC in bearing exposed to electrical
currents.
WEC in bearing test running under mixed
friction and slip.
WEC in bearing test that was hydrogen
charged.
Short Heavy Loads
Standstill Corrosion Electrical Current
Role of lubricant and tribochemistry
Low Film and Slip
Photos from SKF
© SKF Group
• The exact combination of drivers that explains the failures in wind gear units is not yet understood:- Limits of current solutions are not fully understood- A better understanding of critical operating conditions in wind gearboxes still
required• Simulations and measurements complete each other.
Critical Operating Conditions in Wind Gearboxes
Simulation• Requires a detailed set of
boundary conditions• Requires tuning of model
parameters• Disturbances are negligible• Possibility of in-depth
analysis of roller kinematics.
Measurement• Provides data in complex
operating conditions• Only requires to process the
measured signals• Limited number of output
parameters• Measurement disturbances and
input uncertainties.
Photo from SKF
Illustration from SKF
Illustration from SKF
Cons
ConsPros
Pros
Measurement Setup
Photo by Jonathan Keller, NREL 49037
© SKF Group
• Instrumentation focused on high-speed shaft, bearings, and lubricant:- Shaft speed
- Cage speed
- Roller speed
- Shaft torque and bending
- Stray current
- Bearing temperatures
- Air temperature and humidity
- Lubricant temperatures and moisture content
- LogiLube and Poseidon lubricant monitoring and routine oil samples
- SKF iMX8 system.
Winergy PEAB 4410.4 Gearbox and SKF Cylindrical Roller BearingsGearbox Instrumentation
Photo by Mark McDade, NREL 49050
Sliding
Source: Keller, J. and S. Lambert, Gearbox Instrumentation for the Investigation of Bearing Axial Cracking, NREL/TP-5000-70639, 2018.
© SKF Group
GE 1.5 SLE turbine:• Blade flap and edge bending
• Blade pitch angles
• Rotor azimuth and speed
• Main shaft torque and bending
• Active and reactive power
• Nacelle yaw
• Tower bending and torsion
• Wind vane offset
M5 met tower:• Air temperatures and humidity
• Wind speed and direction
And more…GPS time stamped.
Turbine and Meteorological (Met) Tower Instrumentation
Photo by Dennis Schroeder, NREL 21884
GE 1.5 SLEESS Mk 6 controller
M5 Met
Tower
Photo by Dennis Schroeder, NREL 49409
© SKF Group
Roller and Cage-Speed MeasurementCage-speed measurement:• Pin passage detected by
proximity sensor• One speed measurement per
cage revolution.
Roller-speed measurement:• Magnetized roller• Changing magnetic field detected
by coil next to the bearing• Position of magnetized roller
determined by cage pin.
Cage Pin
MagnetizedRoller
Photos by Jonathan Keller, NREL 40979 and 40981
Illustration from SKF
Numerical Model Building and Verification
Illustration from SKF
Illustration by NREL
© SKF Group
Bearing B
Bearing A
• Mean cage speed during each revolution is available
• Instantaneous roller speed is available but highly disturbed
• Operating bearing clearance is unknown (bearing inner ring temperature often not available)
Measurement Limitations and Processing
Processed Rolling Element (RE) Speed vs. Averaged at Stationary, Fully Loaded Operating Condition
Spee
d [rp
m]
Time [s]
Postprocessing of the measurement is necessary:
1. Select time intervals where the cage speed is constant
2. Use several cage revolutions to filter the disturbance of the roller speed
3. Select best measured intervals.
© SKF Group
Measurement Screening1. Systematic detection of all cage-speed plateaus:
Spee
d [r
pm]
Time [s]
2. Least-squares fit of a piece-wise approximation of the roller speed:
Azimuth [deg]
Spee
d [r
pm]
3. Systematic selection based on error:
Spee
d [r
pm]
Azimuth [deg]
Final selection, based on most interesting and diverse
operating conditions to increase the validity of the
semiempirical model.
rpm = revolutions per minute | s = seconds | deg = degree
© SKF Group
• At lower operating temperature, the rollers decelerate significantly more in unloaded zone
• Higher temperature lower viscosity less drag losses on rollers in unloaded zone slower deceleration
Effect of Temperature on Roller Speed: “Down Slope”
0 100 200 300 400
Cage position [deg]
1500
2000
2500
3000
3500
4000
Rol
ler s
peed
[rpm
]
RS
RE speed using averaging
Temp = 36°C0 100 200 300 400
Cage position [deg]
1500
2000
2500
3000
3500
4000
RS
RE speed using averaging
Temp = 57°C0 100 200 300 400
Cage position [deg]
1500
2000
2500
3000
3500
4000
RS
RE speed using averaging
Temp = 67°C
© SKF Group
• A significantly larger temperature difference is measured on bearing B than on bearing A:– Bearing B has much smaller radial clearance and a larger loaded zone than bearing A
• Slower deceleration of the rollers in unloaded zone at increasing temperature (lower oil viscosity)
• Drag losses increase with the size of the roller (larger projected surface of the rollers).
Effect of Temperature and Oil Viscosity – Overview
Tem
pera
ture
Diff
eren
ce[C
]
Time [min]
min = minute | µm = micrometers
Temperature Difference of Bearing RingsClearance as Function of
Temperature Difference of Bearing Rings
Bearing A
Bearing B
© SKF Group
The model is designed by two SKF proprietary software.
SKF Numerical Modelling
SKF BEAST SKF SimProExpert
QJ bearing replaced by nonlinear stiffness.
• Transient multibody dynamic solver
• Detail contact calculation, elastohydrodynamic layer lubrication
• Cage-roller interaction
• Drag losses not automatically modeled.
Linear rotational damping torque is applied to both the cage and the rollers.
Illustrations from SKF
© SKF Group
Analytical Model Predicts Roller and Cage Sliding
Roller dynamics model (analytical):• Harris roller dynamics model
Lubricant hydrodynamics model based on:• Bercea cage friction model• Dowson and Higginson lubricant model
0i o cQ Q F− + =
0ij o v cgF F F Q− + − =
12
ri o cg cg c
dM M DQ Jdωµ ωφ
− + =
Tangential
Radial
Torsional
Primary Governing Equations
Cage
Source: Guo, Y. and J. Keller. Forthcoming. Analytic Formulations of Rolling Element Bearing Sliding in Wind Turbine Gearboxes, Mechanism and Machine Theory.
Frictional Energy Loss
Roller Free Body Diagram
Illustration by NREL
© SKF Group
Parametric Studies To Verify Model ParametersExample in BEAST: Influence
of Rotational Damping
Spee
d [rp
m]
Azimuth [rad]
Example in Analytical Model: Influence of Temperature
Spee
d [rp
m]
Azimuth [rad]
Nms = newtonmeter-second | rad = radian
© SKF Group
Verification of Simulation ResultsSp
eed
[rpm
]
Azimuth [rad]
Torque = 7,930 Nm, TOR ~ 41oC, Toil = 45oCδB = 5𝜇𝜇m, δA = 95𝜇𝜇m
Azimuth [rad]
Torque = 7,930 Nm, TOR ~ 63oC, Toil = 63oCδB = 30𝜇𝜇m, δA = 145𝜇𝜇m
Azimuth [rad]
Torque = 9,520 Nm, TOR ~ 57oC, Toil = 41oCδB = 20𝜇𝜇m, δA = 145𝜇𝜇m
Input
Nm = newtonmeters | TOR = Outer ring temperature | Toil = Oil supply temperature | δ = Clearance
Roller Speeds Roller Speeds Roller Speeds
Measurements at Transient Conditions
kW = kilowatt | LSS = Low-speed shaft | HSS = High-speed shaft | kNm = kilonewtonmeter
Pow
er, T
orqu
e an
d Sp
eed
Drivetrain Conditions during Emergency Stop
© SKF Group
Transient Conditions – Emergency Stop
21:49:00 21:49:10 21:49:20
Mar 04, 2018
-500
0
500
1000
1500
2000
Power [kW]
Torque LSS [kNm]
HSS speed [rpm]
21:49:00 21:49:10 21:49:20
Mar 04, 2018
-1000
0
1000
2000
3000
4000
5000
Rol
ler s
peed
[rpm
]
Roller speed at emergence stop: RS
Measured
Theoretical
21:49:00 21:49:10 21:49:20
Mar 04, 2018
-1000
0
1000
2000
3000
4000
5000
6000
Rol
ler s
peed
[rpm
]
Roller speed at emergence stop: GS
Measured
Theoretical
• Torque oscillations at drivetrain 1st
eigenfrequency• Oscillations result in cage and roller dynamics• Rotor side more sensitive to torque oscillations
than generator side• Roller speed measurements unreliable at low
speed conditions.• At brake engagement roller speed reduces to
about 80% slip and accelerates back in about 1.5 seconds.
Rotor Side Generator Side
Pow
er, T
orqu
e an
d Sp
eed
Drivetrain Conditions
21:49:00 21:49:10 21:49:20
Mar 04, 2018
0
100
200
300
400
500
600
700
Cag
e sp
eed
[rpm
]
Cage speed at emergence stop: RS
Measured
Theoretical
21:49:00 21:49:10 21:49:20
Mar 04, 2018
0
100
200
300
400
500
600
700
Cag
e sp
eed
[rpm
]
Cage speed at emergence stop: GS
Measured
Theoretical
Rotor Side Generator Side
© SKF Group
Transient Conditions – LVRT (50% Drop for 300 milliseconds)
21:46:00 21:46:04 21:46:08 21:46:12 21:46:16 21:46:20
Mar 05, 2018
0
200
400
600
800
1000
1200
1400
1600
1800
Power [kW]
Torque LSS [kNm]
HSS speed [rpm]
21:46:00 21:46:04 21:46:08 21:46:12 21:46:16 21:46:20
Mar 05, 2018
2500
3000
3500
4000
4500
5000
5500
6000
Rol
ler s
peed
[rpm
]
Roller speed at LVRT: GS
Measured
Theoretical
21:46:00 21:46:04 21:46:08 21:46:12 21:46:16 21:46:20
Mar 05, 2018
1000
1500
2000
2500
3000
3500
4000
4500
Rol
ler s
peed
[rpm
]
Roller speed at LVRT: RS
Measured
Theoretical• Torque oscillations at drivetrain 1st
eigenfrequency after Low-Voltage Ride Through (LVRT)
• Load oscillations resulting in cage and roller dynamics
• Roller speed reduces to about 50% slip and accelerates back in about 0.5 seconds.
Rotor Side Generator Side
21:46:00 21:46:04 21:46:08 21:46:12 21:46:16 21:46:20
Mar 05, 2018
460
480
500
520
540
560
580
600
620
Cag
e sp
eed
[rpm
]
Cage speed at LVRT: RS
Measured
Theoretical
Rotor Side
21:46:00 21:46:04 21:46:08 21:46:12 21:46:16 21:46:20
Mar 05, 2018
500
520
540
560
580
600
620
640
660
Cag
e sp
eed
[rpm
]
Cage speed at LVRT: GS
Measured
Theoretical
Generator Side
Pow
er, T
orqu
e an
d Sp
eed
Drivetrain Conditions
© SKF Group
• Operating at low load results in much higher slip levels.
Roller Speed at “Curtailment”1500 kW 250 kW
Rotor Side
Generator SideInboard
Future Steps and Conclusions
Photo by Dennis Schroeder, NREL 49418
© SKF Group
• Repeat the procedure for the cage speed at low load. The proximity sensor is not affected by the same disturbance as the induction coil.
• Simulation of transient conditions (i.e., when measurement cannot be efficiently filtered from noise).• Use simulation results to evaluate critical conditions for the bearings (e.g., by power slip density or
cumulative frictional energy).
Ongoing Steps
Pow
er S
lip D
ensi
ty [W
/mm
2 ]
Azimuth [rad]
Spee
d [rp
m]
Azimuth [rad]
Roller Speed Frictional EnergyPower Slip Density
W/mm2 = watts per millimeters squared | J/s = joules per second
Azimuth [rad]
Fric
tiona
l Ene
rgy
[J/s
]
© SKF Group
• Measurement of roller and cage speed gives useful insight in the bearing kinematics at different operating conditions:– Low load/curtailment– Emergency stop– LVRT
• High roller slip and accelerations have been measured at these events• BEAST model has been built and shown to be able to accurately predict roller and cage
behaviour at different loads and temperature• Next steps:
– Apply and validate the models at special events– Evaluate the roller slip losses at special events.
Conclusions
© SKF Group
Thank you for your attention!Vaes, D., Y. Guo, P. Tesini and J. Keller. 2019. Investigation of Roller Sliding in Wind Turbine Gearbox High-Speed Shaft Bearings (Technical Report). NREL/TP-5000-73286. National Renewable Energy Laboratory (NREL), Golden, CO (US). http://www.nrel.gov/docs/fy19osti/73286.pdf
This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office and CRADAs 16-608 with SKF GmbH and 17-694 with Flender Corporation. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.