The%20Effect%20of%20Gearbox%20Architecture%20on%20Wind%20Turbine%20Enclosure%20Size

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The Effect of Gearbox Architecture on Wind
Turbine Enclosure Size

• Charles D. Schultz, PE
• Beyta Gear Service
• Winfield, Illinois

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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

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Typical Wind Turbine Complete Gear Set 3PPH
arrangement
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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

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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

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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

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Gear Arrangements Considered

• All external gears
• Multiple planetary stages
• Single planetary stage with multiple external
  stages

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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

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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

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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
• 2372.47 hp x 2.7 6405.669 hp
• (6405.669/4023 RDC).333 1.1677
• Rating for 1.1677 NDP 1494.42 x 2.7 4034.934
  HP
• 4034.934/4023 1.003
• .3 error is due to dynamic factor changing

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Arrangements to the same scale
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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

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Number of planets vs. ratio
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Envelope vs planets
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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 401 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 601 to 1201 ratio range

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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?

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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