section_path: History/Discovery and use/Hydrogen-cooled turbogenerator
section_name: Hydrogen-cooled turbogenerator
paragraph_text: Hydrogen-cooled turbogenerator
  
  The first hydrogen-cooled turbogenerator went into service using gaseous hydrogen as a coolant in the rotor and the stator in 1937 at Dayton, Ohio, owned by the Dayton Power & Light Co. This was justified by the high thermal conductivity and very low viscosity of hydrogen gas, thus lower drag than air. This is the most common coolant used for generators 60 MW and larger; smaller generators are usually air-cooled.