Why can't a 2 pole ac induction motor run a 6 pole induction generator

  • #1
Elijah Castiel
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TL;DR Summary
The argument is, if I have a 2 pole, 2kw motor, shaft connected to a 6 pole, 4kw generator, why will this not run?
I will use examples of actual products:

1) 3 hp (2.2kW) 3 phase 2 pole AC Induction Motor
3 hp/2.2kW three-phase induction motor features 2 poles, 2840rpm rated speed, and 7.4Nm nominal torque, with a working voltage of 380V 50Hz. Cheap 3-phase asynchronous motor has outstanding performance in the price, maintenance, reliability, durability, and operation.

2) 5 hp (5.5kW) 3 phase 4 pole AC Induction Motor
Cheap 3 phase AC induction motor or asynchronous motor, 4 pole 1440rpm, squirrel-cage type, 7.5 hp (5.5kW) nominal power with 380 Volts @ 50Hz voltage, Totally Enclosed Fan Cooled Enclosure, foot mounting, high-efficiency performance, high starting torque, little vibration, and reliable operation.

What I will then do is, turn 2) into a generator that is self-excited and use 1) to operate it.

With the idea that I only need the torque from 1) to get 2) to 103% of 1440 rpm.

Is this possible?

if not, why?

If so, why?

Thanks,
 
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Answers and Replies

  • #2
anorlunda
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I'm not sure about your details. But you can't violate conservation of energy ever. Meaning, you can never get 4kW from 2kW, no matter what kinds of devices you use.

Also be reminded that free-energy, perpetual motion, and over-unity power gain are all forbidden topics here on PF.

So, is your meaning to get more power out than power in?
 
Last edited:
  • #3
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To generate 5.5 kW from 1440 rpm you need a minimum torque of 5.5kW/(1440*2pi/minute) = 36.5 Nm. More if you take into account that the generator is not 100% efficient. Not surprisingly, you can't get this with half the input power.
 
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  • #4
berkeman
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if I have a 2 pole, 2kw motor, shaft connected to a 6 pole, 4kw generator
If you put 2kW into the input motor, at most you can get 2kW out of the generator that you drive with that motor's output shaft.
 
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  • #5
anorlunda
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Thread closed because it violates PF guidelines.
 

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