Lesson 1/Learning Event 2
The major advantage of air cooling is that the generator and cooling are self-contained, drawing air
from the environment. However, fan power requirements can become excessive at high speeds
because fan designs usually are structured to provide sufficient cooling at the lowest speed
corresponding to rated output. Fan power at high speeds then appears as a severe reduction in
generator efficiency. Another factor is that, unless it is filtered, cooling air can deliver abrasive
particles, water, or other substances to the generator interior. Furthermore, rotor and stator design
must permit unrestricted passage of air through the generator. This can be accomplished by
designing passages through the rotor and stator. However, roughness in the surface of the rotor
contributes to windage losses, further affecting unit efficiency.
AC GENERATOR REGULATION
FIGURE 14. AC AND DC REGULATOR COMPARISON.
The regulation of AC generator output, though just as important as the regulation of DC generator
output, is much simpler for the following reasons: