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

In summary, 2 pole AC induction motors and 6 pole induction generators cannot be used together due to their different designs and functions. It is not possible to modify a 2 pole motor to run a 6 pole generator, and there are other factors such as speed of rotation and frequency that make them incompatible. These devices cannot be connected in any way, but there are alternative solutions such as using a variable frequency drive or a gearbox to achieve the desired outcome.
  • #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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  • #2
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?
 
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  • #3
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
Elijah Castiel said:
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
Thread closed because it violates PF guidelines.
 

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

This is because the number of poles in an induction motor and an induction generator must be the same in order for the motor to run the generator. This is due to the principle of electromagnetic induction, which states that a changing magnetic field is necessary to induce a current in a conductor. With mismatched pole numbers, the magnetic fields of the motor and generator will not be in sync, preventing the generator from producing electricity.

2. Can a 2 pole ac induction motor be converted into a 6 pole induction generator?

No, it is not possible to convert a 2 pole induction motor into a 6 pole induction generator. The number of poles in an induction motor is determined by the design of the motor, and cannot be changed without major modifications to the motor's construction. It is more practical to use a separate 6 pole induction generator for power generation.

3. Why do induction motors and generators need to have the same number of poles?

As mentioned before, the principle of electromagnetic induction requires a changing magnetic field to induce a current. In an induction motor, the rotating magnetic field created by the stator's poles interacts with the rotor's conductors to produce torque. In an induction generator, the rotating magnetic field created by the rotor's poles interacts with the stator's conductors to produce electricity. If the number of poles is different, the magnetic fields will not be in sync, resulting in inefficient or no operation.

4. Are there any exceptions to the rule of matching pole numbers in induction motors and generators?

Yes, there are some specialized designs of induction motors and generators that do not follow this rule. For example, a wound-rotor induction motor can be used as a generator with a different number of poles, but it requires additional components and a different control system. However, these exceptions are not common and are not typically used in industrial or commercial applications.

5. Can a 2 pole induction motor and a 6 pole induction generator be connected in any other way to make them work together?

No, the only way for an induction motor and generator to work together is for them to have the same number of poles. Attempting to connect them in any other way, such as through a gearbox or a belt drive, will not be effective and may even damage the equipment. It is important to always match the pole numbers when using induction motors and generators together for efficient and safe operation.

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