However, real generator is not
similar. It is because surface is proportional to n2 thoughthe loss is proportional to n3. Cooling ability is considered
to be proportional to surface area without additional
cooling. (The reasons why generator is not similar
are of course in problems on electric insulation, centrifugal
force of rotor of large radius, vibration due to
larger shaft, and so on except cooling problem.) If the
output power is proportional to the volume, we have
no scale merit. Then cooling is very important for high
performance of generators.