Design and development of megawatt wind turbines - Wind Power Generation and Wind Turbine Design - page 228

Figure 26: Bedplate mass - options compared to the industry study set.

be accommodated in the actual spaceframe design. The factor K illustrates the idea
of normalizing entitlement of the isogrid and tubular cylinder for adding mass
back into the idealized tubes to account for the main shaft bearing support, drive-
train torque and yaw deck features relative to the conventional and double T frame.
This makes it more of an apples-to-apples comparison. The 1.33 factor is purely
an estimate to make the point, and may need to be higher to yield an acceptable
design. The "optimized" isogrid cylinder would have mass strategically added to
address local high stress regions for a particular spaceframe design making it
comparable to the rolled plate cylinder.
To minimize mass to the greatest extent possible, and take full advantage of an
enveloping spaceframe type structure, large 7 10-MW WT designs will likely

need to incorporate some form of spaceframe-integrated drivetrain technology.
There are some OEMs starting to move in this direction.

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4.4.6 Machine head mass
Today's mainframe and drivetrain components and their protective housing (i.e.
nacelle) are collectively referred to as a MH. The MH mass (MHM) is an impor-
tant consideration for larger WTs because of shipping logistics, fi eld assembly and
installation crane requirements among other things.
The solid line in Fig. 27 is an estimate of the industry study set trend for increas-
ing MHM with larger WTs. The dashed line is the trend for the 10-turbine analysis
group. Future large WTs in the 7

10-MW size range will need the overall MHM
targeted for the solid line or below to ensure favourable WPP economics. The
considerable divergence for the calculated trend at the larger MW ratings illus-
trates why straight scaling of existing drivetrain, bedplate and MH technologies
will not result in a cost-effective WPP.

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