On gearboxes and generators

I have read your informative article on the elimination of gearboxes in wind turbines and the potential for use of permanent magnet generators (PMGs) with a great deal of interest (Windpower Monthly, November 2008). Of course, I appreciate that you mention the NewGen concept developed and promoted by my company, correctly citing the relevant figures. The information, however, that Ed Spooner was the original designer of the NewGen concept was wrong. I know Ed Spooner quite well, but he and I developed our concepts quite independently of each other.

The NewGen generator was originated by myself and is today marketed by VG Power in Vasteras, Sweden, which is chiefly a manufacturer of generators for hydropower with a history from Alstom and ABB Generation. The main point is that the generator bearing is distributed as a set of steel wheels around the periphery of the large diameter generator rotor, which is the explanation of the shorter load paths and lower weight. The tensioned "bicycle wheel" spokes that you refer to as providing a strong, lightweight design are more a coincidence, not critical for the concept. The design is further explained in a paper presented at the European Wind Energy Conference in 2007.

Furthermore, I have a few questions. Does the Multibrid 5 MW turbine have a two-stage gear as the picture caption states, or single-stage gear as stated in the body of the article? And does the Winwind 3 MW unit really have a two-stage gearbox? Others have reported it as one-stage and that is what I have always believed.

The discussion about a possible double fed induction generator (DFIG) in a Siemens direct drive generator is a little confusing. As I understand it, an induction generator will be far to heavy as a direct drive, so this cannot really be up for consideration. If it is a DFIG, it would have a wound rotor and then it would be much better to design it as a very conventional synchronous generator, with active electro-magnetism. And then, as you point out, it would be even better to use PMGs instead.

The concept of a wheel generator with spokes was developed by Ed Spooner in England. The connection with the NewGen design of similar appearance, made in our article last month, was an error we regret.

The Multibrid wind turbine has a single-stage of gearing, not two, as does the Winwind turbine. Again we regret these errors contained in picture captions, not in the text of the article.

With regard to Siemens' research project, there was no intention to imply that Siemens had considered using a DFIG as an option in its experiments with a direct drive turbine. As stated in the article, Siemens rejected use of a DFIG outright.