These units are equipped with one or two internal fans to direct the enclosed air up and through an array of stainless steel tubes, which are mounted on top of the generator. Air from a second external fan is directed through an outer sheet metal enclosure to cool the tubes, and air is then exhausted on the opposite side of the generator. 

Sixty Hz units are available in the following ranges: 720 & 900 RPM up to 5 MW; 1200 RPM up to 6.5 MW; 1800 RPM up to 10 MW.

Fifty Hz units are available in the following ranges: 600 & 750 RPM up to 4 MW; 1000 RPM up to 5.5 MW; 1500 RPM up to 8.5 MW.