Are wind turbines getting too big for planetary gearboxes?

[Windward]

A few years ago, on the condition that I keep it confidential, a prominent gearbox designer gave me a paper he had written on an advanced design for a wind turbine planetary gearbox. I don't believe I am betraying his confidence by quoting the following statement from the paper. It seems to me that this would be common knowledge in the gear industry:

"...There is currently [2012] good capacity for precision gear making to 3 meters in diameter and more limited capacity to 6 meters. This would allow competitive costing [for his design] to approximately 6 MW..."

Now that wind turbines of 15 MW or higher are under discussion, and if they are intended to be planetary-geared turbines, it seems that the gearboxes would require ring gears that would be too large to manufacture at an acceptable cost, if it is even possible to produce them. I would like to know whether I am missing something here.

Direct drive is an alternative for these larger turbines, but that is a subject I would like to avoid. I regard direct drive as folly, at least for turbines larger than about 1 MW.

For a better explanation of what I am getting at, see my paper "Abandon the planetary gearbox design for wind turbines."

 

[drawoh]

Windward,

I don't work in that industry. Wind turbines could be made too large for existing planetary gearboxes. That should not stop you from designing a larger, higher capacity gearbox.

Why can't I design coils optimized for the speed of a wind turbine? I assume the gearbox is a speed increaser. I need efficiency, and a long life from the gearbox, at a reasonable cost, without blocking airflow. Do you have a better suggestion?

--
JHG