Utilization of Hydrogen gas as the cooling medium either for inner-cooled or for conventional type hydrogen cooled units has the following advantages:
- Hydrogen gas is small in density; therefore decrease windage and ventilation loss.
- Hydrogen gas has large thermal conductivity and surface heat transfer coefficient, Therefore, the output per unit volume of active material will increase and the limit of maximum practical rating can be made larger than with an air-cooled unit.
- Freedom from oxygen and moisture results in little corona effect, thereby prolonging the insulation life of the stator coil.
- Small gas density and closed ventilating system will reduce noise.
- Hydrogen-cooled machine is convenient for converting into an outdoor type.
-Common gases which are much lighter than air are (hydrogen and helium). Although helium is inert non-flammable, and an ideal medium for ventilating purposes, it cannot be obtained in quantities, which makes its price high and makes it unsuitable as cooling medium,
-On the contrary, hydrogen can be obtained rather inexpensively, and it has advantages over helium in having a small density and better thermal characteristics.