Cornell Wind Workshop – 6-13-2009 Challenges of Large MMW Challenges of Large MMW Gearboxes in Wind Turbine Gearboxes in Wind Turbine Applications Applications Michael Sirak, PE, GE Transportation Michael Sirak, PE, GE Transportation Tony Giammarise, GE Transportation Tony Giammarise, GE Transportation Cornell University Cornell University 12-13 June 2009 12-13 June 2009 GE Transportation Industry Trends DriveTrain Description Challenges Moving Forward Design Manufacturing Validation
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Cornell Wind Workshop – 6-13-2009 Challenges of Large MMW Gearboxes in Wind Turbine Applications Michael Sirak, PE, GE Transportation Tony Giammarise,
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Cornell Wind Workshop – 6-13-2009
Challenges of Large MMW Challenges of Large MMW Gearboxes in Wind Turbine Gearboxes in Wind Turbine ApplicationsApplications
Michael Sirak, PE, GE Transportation Michael Sirak, PE, GE Transportation Tony Giammarise, GE TransportationTony Giammarise, GE Transportation
Cornell UniversityCornell University 12-13 June 200912-13 June 2009
GE Transportation
Industry Trends
DriveTrain Description
Challenges Moving Forward
Design
Manufacturing
Validation
Cornell Wind Workshop – 6-13-2009
GE … a tradition of innovation
Founded in 1878 as theEdison Electric Co.
130 years of successful operation
320,000 employees worldwide
Strong technology focus … Research centers in Germany, India, China and the U.S.
• Torque Arm Design – Currently used for a 1.5-2.0MW turbine Gearbox, but as the MW rating increases, this design becomes complex
• Adequate Cooling & heating – Challenge due to extreme environmental conditions
• Noise control – Huge factor due to noise regulations
• Vibrations
• Seal designs – Current Gearbox industry is challenged is oil leaks either on input side / output side
• Reliability – Design life 20 years
• Weight – Shipping and uptower
Flap Flap deflectiondeflection
Edge Edge deflectiondeflection
Tower Tower loadsloads
Main Shaft Main Shaft MomentMoment
NacelleNacelleYawYaw
Flap Flap deflectiondeflection
Edge Edge deflectiondeflection
Tower Tower loadsloads
Main Shaft Main Shaft MomentMoment
NacelleNacelleYawYaw
Cornell Wind Workshop – 6-13-2009
Growing wind turbine scale necessitates development of new drive train technology
Roller Speed: 92 ft/s
Roller Speed: 65 ft/s
RotationRotation1,500 RPM
3.6 MW HS Pinion Bearing
Rotation1,500 RPM
1.5 MW HS Pinion Bearing
Problem
•Conventional 3-stage gearbox-based drive trains are sub-optimal as wind turbine rated power grows from 1 MW to 5 MW
•Cause is increasing size of problematic HS Pinion Bearings which require decreasing oil viscosities
•Forces a dangerous compromise … select low viscosity oil to support higher speed bearings OR higher viscosity oil to protect the low speed gear stages
Solution
•Develop technology that eliminates the need for the 3rd (high speed) stage of the gearbox
• Shipping & Logistics – Weight & shape of the Gearboxes causing a challenge for shipping & logistics
• Condition based monitoring system – Proactively monitors, detects impending drive train issues, enabling increased availability & decreased maintenance costs
• Uptower Inspection Technology – Barkhausen Noise, Eddy Current
• Can only climb two or three towers per day!
Wind farms in Ocean- greater challenge for maintenance
Large Cranes Used for installation, repair & accessibility
Cornell Wind Workshop – 6-13-2009
Barkhausen Noise – Uptower Inspections
.
No other teeth had comparative BH values as the damaged teeth. GB was repaired and placed back in service.
1sttooth
2nd tooth
1sttooth
2ndtooth
Surface defect Caused by grind temper
Leveraging uptower inspection and repair
Cornell Wind Workshop – 6-13-2009
Gear Case Depth Eddy Current Inspection
DescriptionGE-conceived technology that enables non-destructive examination of Gear manufacturing quality
Benefits•Advances state of the art in gear
manufacturing and wind turbine gearbox quality
•Eliminates need for sacrificial parts during gear manufacturing
•Reduces gear inspection process cycle time … manufacturing productivity improvement
•Enables examination of gears after installation in the gearbox
Eddy Current System
Gear Case Depth Profile
0
10
20
30
40
50
60
70
2000 3000 4000 5000 6000 7000 8000 9000 10000
Distance from Edge (µm)
Rc
scan 1
scan 2
scan 3
Gear Case
Case
Cornell Wind Workshop – 6-13-2009
Location of 2 MW generator coupling
3.5 MW IntegraDrive in
the space of a 3-stage 2.3 MW
gearbox
Turbine Efficiency Comparison
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
P/P rated
Effici
ency
IntegraDrive
Standard DFIG
Conventional Gbx &
Generator
IntegraDrive
No. of Bearings 26 11
No. of Gear Meshes 15 6
Efficiency Range 96.5% - 97.0% 99.3%
System Efficiency 90% 93%
Generates 6% higher AEP versus conventional DFIG drive train
Modular flywheel coupling system … common interface for
multiple suppliers
Compound Planetary Gearbox
PM Generator
IntegraDrive geared generator
Cornell Wind Workshop – 6-13-2009
Challenges of Design, Manufacturing Validation of large Gearboxes used in wind Turbine Applications
June 12-13 2009, Cornell University
Mike Sirak
Tony Giammarise
Cornell Wind Workshop – 6-13-2009
X section of a typical 1.5 MW Wind Turbine Gear Drive converts
~ 18 rpm input to 1440 rpm output; hence a speed increasing drive system
GE Energy has the entire system. We at Power Drives are building only the Gear drive portion of the system
This is a talk to show you some of the hardware, and the manufacturing methods/ materials used
Cornell Wind Workshop – 6-13-2009
Stats for a typical 1.5 MW system
Cut in wind speed 3.5m/s
Cut out Wind speed 25m/s
Rotor diameter 77m
Rotor speed 11.0 to 20.4 rpm
Swept Area 4657 m2
Tower height 80 to 100 m
Near Future 2.0 to 2.5 MW near term, land based (already here in Europe)
Stats for a mating gearbox
Input rpm 18
Output rpm 1440
Ratio 85.71
Input power 1660Kw
Input rated Torque 947000 Nm
Cornell Wind Workshop – 6-13-2009
The practical issues with Big wind machines and the scale of things :
• Installation
• logistics and access
• Scale reflected in cost and available suppliers; their capacity and location, logistics
• Unscheduled maintaince
~240 ft, (80 m)
sky hook
Cornell Wind Workshop – 6-13-2009
Gearbox Design is based on a design process where requirements are flowed to Drive Systems from:
•Turbine manufacturers
•public standards
•insuring bodies
•Internally imposed guidelines
Typical Design deliverables include
•Geometrical/Dimensional envelope, details in aux equipment placement
•Power capabilities, input rpm’s output rpm’s
•Weight limit
•Environmental operational conditions
•Temperature extremes
•Wind class
•Emergency stops/overload conditions
•Noise limits
•Reliability guarantees
•Certification from insuring body
Cornell Wind Workshop – 6-13-2009
Gear box materials flow from design requirements, customer requirements and insurance bodies
Structural Components
Moderately large Machined Ductile Iron Castings with
Soundness requirements
Mechanical and Microstructural requirements
Environmental Requirements (Cold weather, -40C)
Gearing
Forged raw materials
Clean Steel Technology required for gear steels
Carburized and hardened
Extensive high tolerance machining AGMA class 12 and higher
Extensive Secondary heat treatments/ finishing operations/ inspections for final acceptance
Cornell Wind Workshop – 6-13-2009
Bearings
Extensive use of rolling element bearings
~ less than 10% mass of a 1.5 MW gear box are the bearings
Commercially produced by the leading global bearing suppliers
Clean steel technology required
Both thru hardened and case carburized utilized
Bearing issues:
design loads and their complete measurement
Global supply issues of capacity timely deliveries
Earlier generation of gear boxes had life limited bearing failures
.
Cornell Wind Workshop – 6-13-2009
20000 lbs of 32000 lbs total of the gearbox mass for a 1.5 MW Box is structural castings. Half of that is in one casting.
Cornell Wind Workshop – 6-13-2009
First stage planetary gears carrier cast ductile iron
Heavy walled Ductile Iron Issues
•Designing for optimized weight to strength ratios
•Soundness of castings and surface quality
•Consistency of Mechanical properties and microstructure throughout
•Cold weather requirement and fracture toughness measurement
•Global supply chains also represent additional manufacturing/ quality risks
Cornell Wind Workshop – 6-13-2009
Ductile (spheroidal) Iron metallurgy
What it it?
Why Ductile?
Standard structural material, Effectively easy to cast, Lower costs as compared to cast steel, better yields and comparable mechanical properties, machines readily, and insuring bodies allow it!
Properties
Common grade used by many Wind turbine producers
100X Microstructure ferritic ductile Iron
Cornell Wind Workshop – 6-13-2009
Other structural Castings found in wind turbine system are similar to those within the gear box.
Hub Casting
Bedplate Casting
Cornell Wind Workshop – 6-13-2009
Bearing locations in a 1.5MW compound planetary gear arrangement
Bearings shown in various colors
Cornell Wind Workshop – 6-13-2009
Examples of Roller bearing types and usage within a 1.5 MW gear box
Cornell Wind Workshop – 6-13-2009
Overview of Wind Gearing
Forged raw materials using
Clean Steel Technology & high Hardenability Steels
Carburized and hardened helical gearing
Extensive high tolerance machining AGMA class 12 and higher for reduction of noise, better load sharing
Extensive heat treatments/ finishing operations/ inspections for final acceptance
Cornell Wind Workshop – 6-13-2009
Clean Steel Technology a Definition
Timken Para-premium
ESR requirement
Steel cleanliness by various melting methods
Air melt requirement
Steel making methods utilized for Clean Steel
•Bottom taping EAF
•Ladle refined
•Deoxidized
•Vacuum degassed
•Bottom poured ingot or con-cast
•Protected from re-oxidation during teeming/casting
•Careful limits on Hydrogen and Oxygen
All of the above need to be done to assure high quality steel
Increasing cost
2x
X
Decreasing steel quality
Double melting
Single melted standard air
Gear & Bearing quality
Cornell Wind Workshop – 6-13-2009
Manufacturing sequence for typical precision Wind gears
Steel making/ ingot production
Grades 18CrNiMo7-6, 43B17, 4820 and similar
Clean steel technology required/ No naughty bits in the steel/ inspect it
Forging operations to rough shape ingot into forged blank
heat it/ beat it / heat treat it and then inspect it
Gear making operations
rough it, hob it ( First outline of the tooth form )
prep it for carburizing
pump carbon into the surface (Extensive diffusion based high temperature controlled cycles changing the near surface to a different alloy!)
quench it to make it hard
temper it to make is a little less hard but improve it’s toughness
grind it to very accurate finish dimensions
inspect it, measure it, making sure it meets print and is free from manufacturing defects
protect it during storage/shipment
Cornell Wind Workshop – 6-13-2009
Micro Hardness of a tooth Chip
30
35
40
45
50
55
60
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75
distance form ground surface
Ha
rdn
es
s in
HR
C c
on
ve
rte
d f
rom
V
ick
ers HRC;A
HRC;B
HRC;B1
Typical Case Carburized tooth form and the scale of things
Why Case harden gears
•Resist bending Fatigue loads
•Resist Surface contact Fatigue
•Add compressive residual stress to aid in the fatigue loading capabilities
•Core structure remains ductile
•Highest allowable design loads per all international standards
•Large capacity worldwide for this type of hardening process
Case hardening Terms
•Surface Hardness
•Effective Case depth to HRC 50
•Pitch line Case depth
•Root hardness
•Core hardness
A tooth form showing the surface hardening; scale is in mm
Raw material 9310H grade 2 per C50E76 Must from TIMKENcleanliness per ASTM A534 Every HeatHydrogen content besides chemistry Every Heat
Forging From Canton Drop Forging Reduction ratio
Normalize and temper B50E215 Viual check green painting Every piece
Rough Turning Process sheet Dimension check Every pieceDrilling / tapping Process sheet Dimension check Every piece
Forging soundness AGMA 923 grade 2 UT Every piece
Hobbing Process sheet M.O.P check Every piece
Tooth shapping Process sheet M.O.P check Every piece
Chamfer Process sheet Dimension check Every piece
Carb / Quench Hardness, metallurgical test Every heat lot
Shot peen AMS-S-13165 Coverage/saturation Every piece
Hard turning Process sheet Dimension check Every piece
Enternal tooth grinding Process sheet Gear charts / M.O.P Every piece
Internal spline grinding Process sheet Gear charts / M.O.P Every piece
Dynamic balance Process sheet Every piece
MPI AGMA 923 Every piece
Nital etch AGMA 2007 Every piece
Final inspection blue prints Dimension check, visual check Every piece
Typical Gear Quality Checks
Cornell Wind Workshop – 6-13-2009
Modern Gear Grinders required to meet the tolerance needs for wind gearing. High quality tolerances needed to reduce noise
Cornell Wind Workshop – 6-13-2009
Current grinding technology both measures, distributes stock and self corrects dimensions, before and during grinding
The requirements of Wind Gearing also require large capital investments.
Cornell Wind Workshop – 6-13-2009
Gear Tolerances and the scale of things
Typical AGMA Class 12 gearing found on a 40 inch diameter high speed gear
These magnitudes require temperature controlled grinding processes, temperature controlled measurement processes to produce accurate gears. Accurate tooth form assures uniform loading
Small numbers!
Cornell Wind Workshop – 6-13-2009
Issues in gear manufacture for wind gear systems
•Special problems of large forgings
•Distortion during heat treatment
•Distortion during quenching
•Achieving adequate case and or core properties in large parts
•Damaging hard surfaces during final grind operations
•Capacity worldwide for large high tolerance gear manufacture
Cornell Wind Workshop – 6-13-2009
Design success means:
•Understand the requirements
•Know and measure loads
•Utilize knowledge in Public Standards
•Understand the operating environment
•Detail and define requirements and flow them from System, to sub-System, to each component
•Inspect Components using the right methods and technologies
•Manufacture carefully Utilizing the right advanced and traditional tools
•Test to failure
The outcome is, the ability to achieve the level of reliability desired
Thank you
Cornell Wind Workshop – 6-13-2009
Scale of things: 1.5 MW units
1660 Kw = 2226 HP= 1.6 MW
•GE locomotive=4400 HP,so from a power view, half a locomotive up a pole.
•The entire structure, including the pole is ~ 220 Tons excluding the foundation=weight of locomotive
•The foundation weights ~500 tons
Cornell Wind Workshop – 6-13-2009
Lake Superior Late March w/ machines as cold as the photo looks