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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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Presentation on theme: "Cornell Wind Workshop – 6-13-2009 Challenges of Large MMW Gearboxes in Wind Turbine Applications Michael Sirak, PE, GE Transportation Tony Giammarise,"— Presentation transcript:

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

2 Cornell Wind Workshop – 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.

3 Cornell Wind Workshop –




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 Performance 98% Availability 40+% Capacity Factor at IEC-II 8.5 m/s CF% +10 pts in last 5 yrs Clipper

8 Performance Average 45+% Capacity Factor Availability & Cost Not Well Established 11 c/kwhr UK Thames Estuary site Offshore Technology Status Offshore Technology 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 GE 3.6 MW – Arklow Banks

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

10 WinDS Analysis to Achieve 20% 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 Analysis Summary Existing Technology Achieves 6-8% Penetration by % Requires Technology Improvement Improvements In Cost, Capacity Factor, and O&M needed One cent reduction in COE - 12 billion dollar economic savings per year

11 Cornell Wind Workshop – GA87 Gearbox

12 Cornell Wind Workshop – GA87E – 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 Cornell Wind Workshop – 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 mm Overall Length

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

15 Cornell Wind Workshop – 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 Cornell Wind Workshop – Growing wind turbine scale necessitates development of new drive train technology Roller Speed: 92 ft/s Roller Speed: 65 ft/s Rotation 1,500 RPM 3.6 MW HS Pinion Bearing Rotation 1,500 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 3 rd (high speed) stage of the gearbox Impact of change from ISO VG 320 to ISO VG 460 oil on Low Speed Planetary gear film thickness Film Thickness (mm) Above Line: Film Thickness > Gear Surface Finish

17 Cornell Wind Workshop – 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 Cornell Wind Workshop – Gear Design Process

19 Cornell Wind Workshop – Constraints – Manufacturing Perspective 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 IH process Gear Mfg defect- not acceptable

20 Cornell Wind Workshop –

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 Cornell Wind Workshop – Component testing … demonstrated 99% reliability at 95% confidence Input HousingCarrierHigh Speed Gear Bearing

23 Cornell Wind Workshop – Cold ChamberLube System Flow Rate Strain Gauge Testing Systems level testing

24 Cornell Wind Workshop –

25 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 Cornell Wind Workshop – Constraints – Maintenance Perspective 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 Large Cranes Used for installation, repair & accessibility

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

28 Cornell Wind Workshop – 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 SystemGear Case Depth Profile Gear Case Case

29 Cornell Wind Workshop – Location of 2 MW generator coupling 3.5 MW IntegraDrive in the space of a 3- stage 2.3 MW gearbox Conventional Gbx & Generator IntegraDrive No. of Bearings2611 No. of Gear Meshes156 Efficiency Range96.5% %99.3% System Efficiency90%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

30 Cornell Wind Workshop – Challenges of Design, Manufacturing Validation of large Gearboxes used in wind Turbine Applications June , Cornell University Mike Sirak Tony Giammarise

31 Cornell Wind Workshop – 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 Cornell Wind Workshop – Stats for a typical 1.5 MW system Cut in wind speed3.5m/s Cut out Wind speed25m/s Rotor diameter77m Rotor speed 11.0 to 20.4 rpm Swept Area4657 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 rpm18 Output rpm 1440 Ratio Input power1660Kw Input rated Torque Nm

33 Cornell Wind Workshop – 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

34 Cornell Wind Workshop – 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 Cornell Wind Workshop – 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 Cornell Wind Workshop – 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 Cornell Wind Workshop – 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 Cornell Wind Workshop – 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 Cornell Wind Workshop – 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

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

41 Cornell Wind Workshop – Bearing locations in a 1.5MW compound planetary gear arrangement Bearings shown in various colors

42 Cornell Wind Workshop – Examples of Roller bearing types and usage within a 1.5 MW gear box

43 Cornell Wind Workshop – 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 Cornell Wind Workshop – Clean Steel Technology a Definition 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

45 Cornell Wind Workshop – 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 Cornell Wind Workshop – 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 Core regio n Distance in mm from ground surface Effective case depth Surface Hardness

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

48 Cornell Wind Workshop – Typical Gear Quality Checks

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

50 Cornell Wind Workshop – 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.

51 Cornell Wind Workshop – 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 !

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

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