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Challenges of Large MMW Gearboxes in Wind Turbine Applications

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Presentation on theme: "Challenges of Large MMW Gearboxes in Wind Turbine Applications"— Presentation transcript:

1 Challenges of Large MMW Gearboxes in Wind Turbine Applications
Michael Sirak, PE, GE Transportation Tony Giammarise, GE Transportation Cornell University 12-13 June 2009 GE Transportation Industry Trends DriveTrain Description Challenges Moving Forward Design Manufacturing Validation

2 GE … a tradition of innovation
Founded in 1878 as the Edison Electric Co. 130 years of successful operation 320,000 employees worldwide Strong technology focus … Research centers in Germany, India, China and the U.S.





7 Land Based Technology Status
Today’s Land Base Utility Class Turbines 1.5 – 3.0 MW Upwind Configuration 80 – 100 Meter Tower Height Conventional 3 stage gearbox Distributed component drivetrain Full Span Pitch Control Tapered Cylinder Steel Towers ~65 kWhr/kg tower top mass 200 MW + Windfarms Clipper Performance 98% Availability 40+% Capacity Factor at IEC-II 8.5 m/s CF% +10 pts in last 5 yrs

8 Offshore Technology Status
Development and demo stage 19 Projects, 900 MW Installed, shallow water 3 – 4 MW Upwind Configuration 80 m towers Monopile & gravity foundations < 15m Steel Tapered Towers Infrastructure not yet available in US Performance Average 45+% Capacity Factor Availability & Cost Not Well Established 11 c/kwhr UK Thames Estuary site GE 3.6 MW – Arklow Banks

9 US 20% Wind Outlook Wind Resource Technology Issues Grid Integration
US has outstanding wind resource Broadly distributed thru mid-west & west Offshore in NE US Has the Wind Resource Technology Issues Need for technology improvements to compete with cheap coal Offshore wind not mature Turbines 5-10 MW req’d 20% Wind Distributes per Demand & Resource Grid Integration Integration of wind forecasting tools Consolidation of load balance zones System Balkanization a barrier Transmission Corridors an Essential Part of the Solution

10 WinDS Analysis to Achieve 20%
Analysis Summary Existing Technology Achieves 6-8% Penetration by 2030 20% Requires Technology Improvement Improvements In Cost, Capacity Factor, and O&M needed One cent reduction in COE billion dollar economic savings per year Land Technology Improvements Turbine size increasing from 1.5 to 5 MW 20% Reduction In Capital Cost per kW 15% Increase In Capacity Factor 30% Reduction in O&M Costs GW Scale Windfarms Offshore Technology Improvements Turbine size increasing from 3 to 10 MW 20% Reduction In Capital Cost 15% Increase in Capacity Factor 50% Reduction in O&M Costs

11 7GA87 Gearbox

12 7GA87E – 1.5MW 1:78 ratio Compound Planetary
3 stage CP design with helical gearing Straddle mounted planet bearings Flexible, splined ring gear No reversed bending loads on planet teeth One high speed stage Over 1300 produced Oldest fleet at 36 months

13 Current GET Gearboxes Differential Planetary + Parallel Shaft
2.0 – – 18 RPM 1400 – 1900 KNm Input Torque 60:1 – 97:1 Ratio Possibilities Approximate Weight: 39,000 Lbs Horizontal and vertical output shaft 550mm CD 2350 / 2150mm Overall Length 2 Simple Planetaries + Parallel Shaft 2.3 – – 16 RPM Input Speed 1500 – 1920 KNm Input Torque 78:1 – 136:1 Approximate Weight: 46,500 Lbs Horizontal Output 550mm CD 2550mm Overall Length Compound Planetary + Parallel Shaft 1.4 – – 20 RPM 700 – 970 KNm Input Torque 59:1 – 86:1 Ratio Possibilities Approx Weight: 33,000 Lbs Horizontal Output 550mm CD .Working on Vertical Output Shaft for 2009. 2200mm Overall Length

14 Common Gearbox Components 2 Simple Planetary + Parallel Shaft Arrangement
Torque Arms – Transfers torque and wind load to turbine structure Low Speed Annulus Gear – Non-Rotating, fixed to Input Housing. High Speed Pinion Bearings– supports gear and braking loads. High Speed Annulus Gear – Non-Rotating, fixed to Input Housing. Input Housing – Supports gearbox torque and blade loads. High Speed Planet Gears – Typically 3. High Speed Pinion – driven by high speed gear. Drives the generator. Input Carrier – Connects Gearbox to Blades Low Speed Planet Gears – Typically 3, 4, or 5 gears. Meshes with Annulus and Sun Gear. High Speed Gear – fixed to sun gear, drives high speed pinion. Pitch Tube – Conduit for electric or hydraulic supply to blade control system – rotates at rotor speed. Low Speed Sun Gear – Output of first speed increasing Stage. Inputs power to High Speed Planetary Stage High Speed Gear Bearings – Supports Sun Gear & High Speed Gar loads. High Speed Sun Gear – Output of second speed increasing Stage. Inputs power to High Speed Parallel Shaft Stage Input Carrier Bearings – Supports blade loads High Speed Carrier Bearings – Supports Gear loads

15 Constraints – Design Perspective
Design Complexity & challenges Dynamic Loads – Extreme coherent gust winds, Turbulent shear winds Low “Lamda” – Design challenge to maintain Lamda ratios >1 High Torque Density Loads prediction & understanding Torque Arm Design – Currently used for a MW 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

16 Growing wind turbine scale necessitates development of new drive train technology
3.6 MW HS Pinion Bearing Roller Speed: 92 ft/s Rotation 1,500 RPM Film Thickness (mm) 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 Above Line: Film Thickness > Gear Surface Finish 1.5 MW HS Pinion Bearing Roller Speed: 65 ft/s Impact of change from ISO VG 320 to ISO VG 460 oil on Low Speed Planetary gear film thickness Rotation 1,500 RPM

17 Relative Sizes & Conversion of mils & microns
~ Diameter of human hair, thickness of copy paper ~ 0.1mm = 100 microns = .004 inch 1 mil = .001 inch = 25.4 microns 1 micron = 1 m = 1e-6 meters = .001 mm Film thickness on low speed wind bearings ~ 0.15 microns!

18 Gear Design Process

19 Constraints – Manufacturing Perspective
IH process Size of Gearing Size of gears used causes a challenge in manufacturing a quality gear, current industry supported by few suppliers in market Heat Treatment Process Several heat treatment process available but process is generally difficult to monitor and maintain long term process capability Steel Quality Casting & Machining Cleanliness Plays a major role in the overall reliability of the gear box from performance & life stand point Grinding Process Quality Very critical to this business as cost of producing a non-quality part accumulates into a higher maintenance costs Gear Mfg defect- not acceptable


21 Constraints – Validation Perspective
Comprehensive commercial testing Component testing Sub-system testing HALT - Every new production or significant change Field testing - ~ typically 6 months field test Cost – testing costs are expensive but critical Larger gearboxes = larger test stands

22 High Speed Gear Bearing
Component testing … demonstrated 99% reliability at 95% confidence Input Housing Carrier High Speed Gear Bearing

23 Systems level testing Cold Chamber Lube System Flow Rate
Strain Gauge Testing


25 Validates deflection calculations in structures, shafts and bearings
Gear Mesh Pattern All gear contact patterns were good and passed typical acceptance criteria. Gear contact patterns & condition are best indicators of system validation. Validates deflection calculations in structures, shafts and bearings Validates adequate lube flow

26 Wind farms in Ocean- greater challenge for maintenance
Constraints – Maintenance Perspective Large Cranes Used for installation, repair & accessibility Filtration – Lube oil used needs regular filtration & maintenance Contamination of Oil w/metal particles Load Management Monitor noise Periodic oil sampling 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

27 Barkhausen Noise – Uptower Inspections
1 st tooth Leveraging uptower inspection and repair . Surface defect Caused by grind temper No other teeth had comparative BH values as the damaged teeth. GB was repaired and placed back in service. 1 st tooth 2 nd tooth 2nd tooth

28 Gear Case Depth Eddy Current Inspection
Description GE-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 Gear Case Case

29 3.5 MW IntegraDrive in the space of a 3-stage 2.3 MW gearbox
IntegraDrive geared generator Location of 2 MW generator coupling PM Generator Compound Planetary Gearbox 3.5 MW IntegraDrive in the space of a 3-stage 2.3 MW gearbox Generates 6% higher AEP versus conventional DFIG drive train Conventional Gbx & Generator IntegraDrive No. of Bearings 26 11 No. of Gear Meshes 15 6 Efficiency Range 96.5% % 99.3% System Efficiency 90% 93% Modular flywheel coupling system … common interface for multiple suppliers

30 June 12-13 2009, Cornell University
Challenges of Design, Manufacturing Validation of large Gearboxes used in wind Turbine Applications June , Cornell University Mike Sirak Tony Giammarise

31 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

32 Stats for a typical 1.5 MW system Cut in wind speed 3.5m/s
Near Future 2.0 to 2.5 MW near term, land based (already here in Europe) 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 to 20.4 rpm Swept Area m2 Tower height 80 to 100 m Stats for a mating gearbox Input rpm 18 Output rpm 1440 Ratio Input power 1660Kw Input rated Torque Nm

33 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 sky hook ~240 ft, (80 m)

34 Typical Design deliverables include
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

35 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

36 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 .

37 20000 lbs of 32000 lbs total of the gearbox mass for a 1
20000 lbs of lbs total of the gearbox mass for a 1.5 MW Box is structural castings. Half of that is in one casting.

38 Heavy walled Ductile Iron Issues
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

39 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 100X Microstructure ferritic ductile Iron Common grade used by many Wind turbine producers

40 Other structural Castings found in wind turbine system are similar to those within the gear box.
Hub Casting Bedplate Casting

41 Bearing locations in a 1.5MW compound planetary gear arrangement
Bearings shown in various colors

42 Examples of Roller bearing types and usage within a 1.5 MW gear box

43 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

44 Clean Steel Technology a Definition
Decreasing steel quality Single melted standard air 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 Double melting Gear & Bearing quality Increasing cost X 2x

45 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

46 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 Surface Hardness Effective case depth Distance in mm from ground surface Case hardening Terms Surface Hardness Effective Case depth to HRC 50 Pitch line Case depth Root hardness Core hardness Core region A tooth form showing the surface hardening; scale is in mm

47 Typical Carburized Gear Process
Steel Supplier Steel Run (Heat) Ingots 29” square Billets 14.5” round corner 240k lbs 30 ingots/run 1 billet/ingot Gear Supplier Forging Supplier (Q =13) Rough Machining Forgings Mults 1 gear/forging 1 forging/mult 6-8 mults/billet GE Transportation Assembly into Gearbox Heat Treat Carb/Quench Hard turn/ Grinding 2 gears/heat treat 1 gear/grind 1 gear/gearbox

48 Typical Gear Quality Checks

49 Modern Gear Grinders required to meet the tolerance needs for wind gearing. High quality tolerances needed to reduce noise

50 The requirements of Wind Gearing also require large capital investments.
Current grinding technology both measures, distributes stock and self corrects dimensions, before and during grinding

51 Gear Tolerances and the scale of things
Typical AGMA Class 12 gearing found on a 40 inch diameter high speed gear Small numbers! These magnitudes require temperature controlled grinding processes, temperature controlled measurement processes to produce accurate gears. Accurate tooth form assures uniform loading

52 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

53 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

54 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

55 Operating Environment
-40C to +40 C Lake Superior Late March w/ machines as cold as the photo looks Above the Columbia River, mid summer

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