Why Hydrogen Gas is the best cooling medium for rotating machines?

Why Hydrogen Gas is the best cooling medium for rotating machines?

Utilization of Hydrogen gas as the cooling medium either for inner-cooled or for conventional type hydrogen cooled units has the following advantages:

1) Hydrogen gas is small in density; therefore decrease windage and ventilation loss.

2) 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.

3) Freedom from oxygen and moisture results in little corona effect, thereby prolonging the insulation life of the stator coil.

4) Small gas density and closed ventilating system will reduce noise.

5) 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.

SFETY  NOTE.

-The intensity of explosion of an air-hydrogen mixture varies with the proportion of the two gases present, and also has to do with the gas pressure.

-A curve on which the values of intensity are plotted against the properties of gases will be approximately a sine wave having zero values at (4 % and 75 % hydrogen), and reaching a maximum intensity in between.

          -So we have to take care:-

*Hydrogen and air should never be mixed.

*Carbon dioxide should be used as an intermediate gas when changing air to hydrogen, or from hydrogen to air.

*When charging gas, provide vent to the atmosphere from generator.