Review how to prevent premature gearbox damage via mainshaft bearing design, torsional/ extreme load control and/or gearbox bearing upgrades.

1. 1
Preventing Gearbox Damage
from Dangerous Loads
April 17, 2018 • Brian Ray – Chief Engineer

2. 2General Industry vs. Wind Energy?
General Industry:
• “Controlled” loads
• Consistent conditions
• On the ground, robust support
• Controlled stops
Wind Energy:
• Wind constantly changes
dynamic/ transient loads
• Site specific wind conditions
• 100 meters in the air on a
‘flexible’ platform
• Stopping protocols

3. 3Gear Drive Turbine – Main Bearing arrangements
3-Point Mount 4-Point Mount
Two
SRBs
Two
SRBs
Torque arm supports
(2 support points)
2-SRBs (2 support points)SRB (1 support point)
Torque arm supports
(2 support points)
Single
SRB

4. 4Spherical Roller Bearing Features :
10/5/09
• Tolerates Misalignment (1.5°)
• Radial and Thrust Loads (up to 25% thrust)
• Truncated Line Contact (Heathcote Slip)
• Contains Radial and Axial Clearance
• Most prevalently used mainshaft bearing for
on-shore turbines
• Suffer from numerous premature damage modes:
Micropitting Cage Damage Edge Loading Wear & Debris

5. 5Tapered Roller Bearing Features :
• Limited Misalignment – managed via specialized internal geometry
• Handles Radial and thrust Loads (up to 100% thrust)
• Line Contact & true rolling motion
• Adjustable setting / can be preloaded to eliminate clearance
• Viable alternate to solving SRB performance issues
Axial Load
Radial Load

6. 6
Tapered Roller Bearing (TDI)
• Preloaded
• High thrust & radial capacity
• Must control Misalignment
Spherical Roller Bearing (SRB)
• Internal Clearance
• Limited Thrust Capability
• Good for Misalignment
• Limits misalignment through preload
• Accommodates some misalignment
through internal geometry & roller profiles
• Absorbs thrust
• Accommodates misalignment through
clearance and shape
• Transmits thrust to gearbox
Comparison: TDI vs. SRB

7. 7Deflection Analysis: TDI vs. SRB
Displacement
(mm)
SRB TDI
TDI %-
Reduction
Axial -1.008 -0.212 79%
Radial 0.059 0.032 45%
SRB Deflection TDI Deflection
Analytical Results Field Test Results
GE 1.5MW Turbine

8. 8
• Grid Loss
• High Wind Shutdowns
• Curtailments
• Generator Short Circuits
• Resonant Vibration
• Wind gusts
• Turbulent or Shear Winds
• Control Malfunctions
• Sensor Malfunctions
• Other E- Stops
Causes of Severe Transient Loads
Any event that triggers an E-Stop, other
rapid shutdown protocol or disrupts
normal operation
Gearboxes are also subjected to extreme
transient loads for a variety of reasons

9. 9Transient Loads Happen in all Turbines
Siemens
2.3
Vestas
V82
GE 1.5
Gamesa
G87
NEG/Micon
750
Nordex
N54
Mitsubishi
600
GE 1.6

10. 10
What happens during a transient load shift?

11. 11
… with a torsional control device!
• Asymmetric torque setting
provides the ability to damp
torsional energy early before
wind-up can occur
• Reduces torque reversals and
oscillations 50-70%
• Smooth frictional slip
• Slips degrees, not rotations
• Maintenance free
How to Mitigate Damage from Transient Loads?

12. 12
Significant reduction
in frequency and
amplitude of torque
oscillations
Significant reduction
in torque reversals
Operating Torque

13. 13Improved Gearbox Bearings to Better Survive Dangerous Loads
If you can’t control the
external loads, then you
can look at improving
the robustness of the
gearbox itself

14. 14
High Speed Shaft
Planetary Gears
Wind Gearbox Bearing Positions
Planet Carrier
Low Speed Intermediate Shaft
High Speed
Intermediate
Shaft
Main shaft
loads
impact
planet
section Torsional loads
impact parallel
section

15. 15Planet Carrier Bearings
Current Design
• Mostly CRB
• Full Complement
• Black Oxide
Design Trends
• Increased use of TRB
• TS bearings designed for Thrust and
Radial load
• Pre-loaded to eliminate clearance
Upgrade Opportunities
• Limited due to space constraints
Damage Modes
• Bearing thrust flange damage
due to main shaft thrust
• Bearing internal clearance can
lead to planetary brg/ gear
damage
Internal
Clearance
Preload

16. 16Planet Bearings
Current Design
• TRB & CRB
- SRBs in older < 1MW designs
• 2-row & 4-row
• Integrated & non-integrated
• Through hardened
Design Trends
• Bearing integrated in gear
• HT / Material (case carb)
• Black Oxide Requirement
Upgrade Opportunities
• Customized RIC (CRB)
• HT / Material (case carb)
• Black Oxide
• DLC Coating
Damage Modes
• Imbalanced load (4-row CRB)
• Assembly / Setting (TRB)
• Debris damage
• Smearing (CRB)
• Micropitting (CRB)

17. 17
Current Design
• 2 CRB (NJ-Style)
• 2 CRB + Thrust
• Through
Hardened
Design Trends
• CRB + 2-Row TRB
• HT / Material (case carb)
• Black Oxide requirements
Upgrade Opportunities
• HT / Material (case carb)
• Black Oxide
• DLC Coating
Damage Modes
• Smearing / Skidding
• White Etch/ Axial Cracks
• Spalling
High Speed & High Speed Intermediate Bearings
+
+
++

18. 18Gearbox Bearing Solutions
Enhancement White Etch Debris Smearing
Black Oxide +
(early stages)
++
(early stages)
‘DLC’ Coatings ++ +++ +++
Case Carburized +++ +++

19. 19

20. 20From the New Energy Update Program Agenda