Page 236 - Electrical Equipment Handbook _ Troubleshooting and Maintenance
P. 236
SYNCHRONOUS MACHINES
SYNCHRONOUS MACHINES 11.11
● The density of hydrogen is 14 times lower than that of air. Thus, the windage losses of
hydrogen-cooled generators are significantly lower than those of air-cooled ones.
● The heat-transfer properties of hydrogen are significantly better than those of air. This allows
hydrogen-cooled generators to operate cooler than the ones cooled by air. Thus, hydrogen-
cooled generators have many fewer problems than those cooled by air.
● Hydrogen is an inert gas. It does not support corrosion whereas air enhances the corro-
sion rate.
● Hydrogen extinguishes arc-initiated fires while oxygen is required to start them.
However, a large hydrogen leak from the generator can cause a fire or an explosion.
The reason is that a mixture of hydrogen and oxygen containing hydrogen in a volu-
metric concentration of 4 to 76 percent can become explosive. Despite this hazard, most
FIGURE 11.9 Four-quadrant synchronous machine operation.
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