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Induction motor ratings

Induction motor ratings

Induction motor ratings

(OP)
How to explain the fact that AC induction motors for dynamometer applications typically have HP (or KW) ratings for absorbing mode greater than for a motoring mode? At the same time some of motors have identical ratings for both modes of operation. Is there a difference in motor design?

RE: Induction motor ratings

Answer to your first question: The name-plate power is shaft power. It is electric power that heats the motor/generator and limits available power in the machine.

So, when motoring, you have a certain electric power - say P1 - and the shaft power is P1 times efficiency. So shaft power will be around 0.9*P1 (assuming 90 percent efficiency).

But, when braking, the shaft power is always greater than P1 (because of losses in the motor). So, shaft power is around 1.11*P1 (P1/.9)

Answer to your second question: Sometimes, people do not bother about the difference between motoring and braking.

There is a lot more to this and you can read about it in most text books on electric machines.

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