Efficiency of 3 phase AC Induction motors

I have noticed that larger motors (40+ HP) are typically more efficient
than smaller motors, and also there is not as much weight difference
for 6 and 8 pole motors compared to 2 and 4 pole. I have several
questions:

(1) Will a 40 HP motor rated at 90% efficiency have better efficiency
at 20 HP? What about at 10 HP?

(2) What sort of efficiency can be expected if a motor is run for short
times at 2x or 3x nominal torque rating? What are typical duty cycles
and maximum ON times for such conditions?

(3) What could be done to make a 12 pole motor (about 5-10 HP) about
the same size and weight as the same HP 2 or 4 pole motor?

Thanks for any ideas.

Paul E. Schoen

.

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