The Effect of Gearbox Architecture on Wind Turbine Enclosure Size Charles D. Schultz, PE Beyta Gear Service Winfield, Illinois

What was the objective of this paper? Demonstrate the “scaleability” of gear design Examine alternate designs for wind turbine gearboxes Begin a discussion of how design decisions effect overall system size

Typical Wind Turbine Complete Gear Set “3PPH” arrangement

What was the scope of this work? Theoretical work only –not connected to any past, present, or future project Design conditions are relevant but simplified Work limited to gears only

Design Condition Summary In place of a Miners’ Rule load spectrum a 1.5 application factor was used 2mW nominal capacity Gears rated for 85,000 hours of full load life [approximately 10 years of 24/7 operation] 15 rpm rotor speed 7 different output speeds 4 different gear arrangements per output speed

Key Design Decisions Pinion tooth counts Number of planets Allowable face width/pitch diameter ratio No divided power path arrangements due to radial timing concerns All external gearing is carburized, hardened, and ground

Gear Arrangements Considered All external gears Multiple planetary stages Single planetary stage with multiple external stages

Design Procedure Used Establish set geometry at 1 NDP 18 tooth minimum 1.3 minimum Mp 1.0 minimum Mf 1.25 maximum face width/pinion pitch diameter ratio Run ratings for 1 NDP gearsets

Design Procedure Used Calculate NDP needed to achieve required capacity Draw cross section of gear train Approximate size of related rotating parts Calculate weights and volumes Compare results for different designs

Scaleability Example 1 DP gear set 18 x 18 sun/planet 12° Helix 20° NDP 1.25 FW/D ratio (3) planets 2.7 mesh factor Durability limited hp x 2.7 = hp ( /4023 RDC)^.333 = Rating for NDP = x 2.7 = HP /4023 = % “error” is due to dynamic factor changing

Arrangements to the same scale

Effect of increasing number of planets Figure 1 shows the relationship between the stage ratio and the maximum number of planets Figure 2 shows the dramatic effect of increasing the number of planets Load sharing becomes a concern as the number of planets is increased

Number of planets vs. ratio

Envelope vs # planets

Results The planetary arrangements currently in use are a logical choice based upon minimum enclosed volume, lowest weight, and relative cost to manufacture Other arrangements may have potential advantages in terms of serviceability and packaging For total ratios of over 40:1 a two planetary stage/one helical stage arrangement gives the best results Total gear ratio seems to have little effect on GEARBOX cost in the 60:1 to 120:1 ratio range

Suggestions for Further Work How is generator size effected by output rpm? How do “flex pin” arrangements effect the choice of number of planets and overall cost? Can designs be developed to permit “up tower” rebuildability?

Thank You: Noel Davis of Vela Gear Systems Mark Haller of Haller Wind Consulting Octave LaBath of Cincinnati Gear Consulting Amy Lane of AGMA Peer Review Team of AGMA