How does an induction motor generate kW when there is only load and no prime mover?

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Ok, I was wrong, there is another way that involves more hardware, and an up front agreement to NOT define an induction motor's own spinning rotor mass as a form of "prime mover".

If you run a motor up to full speed with a VFD, then command it to decelerate FASTER that the rotor mass (and anything attached to it) will coast to a stop on its own, then what happens is that the relative frequency of the stator, as controlled by the drive, becomes lower than the relative frequency of the rotor. Since the VFD is still applying excitation energy to the stator, and thereby to the torpor as well, you have all of the necessary components of an induction generator. Magnetic field excitation and frequency differential where fR> fS
 
Bugman1400 said:
how an induction motor can generate kW without a prime mover.
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The speed of an induction motor is generally less than that of its rotating magnetic field of the stator. But if the rotor is made to run at a greater speed due to stronger wind as in windmill applications, electrical energy is generated and fed into the grid by the induction motor now acting as a generator.
 
Sahib said:
The speed of an induction motor is generally less than that of its rotating magnetic field of the stator. But if the rotor is made to run at a greater speed due to stronger wind as in windmill applications, electrical energy is generated and fed into the grid by the induction motor now acting as a generator.
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Is the wind not a prime mover in that scenario?
 
kwired said:
Is the wind not a prime mover in that scenario?
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Energy can neither be created nor be destroyed but may be converted from one form to another and in this case energy in the prime mover (wind) to electrical energy. :happyyes:
 
Bugman,

If you accept the comments the some of the posting "Experts", thus far, but you haven't accepted the IEEE definition of an induction generator, then I can't help!

Regards, Phil
 
An induction machine driven above synchronous speed by an external source of mechanical power.

OK, I accept it. What is the external source of mechanical power (prime mover)? Or, is there something else that allows the motor to generate kWs?
 
Bugman1400 said:
An induction machine driven above synchronous speed by an external source of mechanical power.

OK, I accept it. What is the external source of mechanical power (prime mover)? Or, is there something else that allows the motor to generate kWs?
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If you are dealing with a short circuit fault in the system, then the inertia of the motor and the driven equipment will supply the power for a short time. That is the motor contribution to short circuit amps.

As for a motor contribution in a steady state system with stable grid power, I also do not see how adding too much PF correction could cause a motor to generate for very long.
 
Sahib said:
Energy can neither be created nor be destroyed but may be converted from one form to another and in this case energy in the prime mover (wind) to electrical energy. :happyyes:
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I do not disagree with that, but pretty sure that is not what this thread is about.
 
Bugman1400 said:
An induction machine driven above synchronous speed by an external source of mechanical power.

OK, I accept it. What is the external source of mechanical power (prime mover)? Or, is there something else that allows the motor to generate kWs?
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???
Prime mover = "an external source of mechanical power"

What part of this is what you don't understand?

Prime mover could be wind turbine, water turbine, diesel or gas engine, tidal pendulum, giant rubber band stretched on a wooden spool, 1 million hamsters on an exercise wheel, anything that makes something rotate that can be coupled up to the shaft of the induction machine.
 
Sahib said:
Then surely Bugman1400 must be joking!
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I'm pretty sure this thread is a spin off from an off topic comment in another thread.

So how does an induction motor generate power that it did not already put into the load without a prime mover acting on that load, and how is wind driving a propeller not a prime mover in such an application?
 
kwired said:
I'm pretty sure this thread is a spin off from an off topic comment in another thread.

So how does an induction motor generate power that it did not already put into the load without a prime mover acting on that load, and how is wind driving a propeller not a prime mover in such an application?
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Agreed.....the question still remains how can an induction motor generate kW without a prime mover. And no, I am not counting during coastdown from the inertia of the rotor, its shaft, and whatever inertial mass from the load.
 
how can an induction motor generate kW without a prime mover

You sell the induction motor and buy a big pile of batteries and an inverter ? Nothing mechanical moving, so fits the definition ?

Akin to the famous physics test question: How do you find the height of a skyscraper with a barometer?

Ans: You knock on the building super's door, say: "hey, I'll give you this keen barometer if you tell me how tall the building is" !
 
If it happens to be sitting next to something creating a changing magnetic field I'll bet you could find a couple of volts on the stator leads.

Other than that, I think you need to glue rare earth magnets all over it and sprinkle it with pixie dust
 
Jraef said:
???
Prime mover = "an external source of mechanical power"

What part of this is what you don't understand?

Prime mover could be wind turbine, water turbine, diesel or gas engine, tidal pendulum, giant rubber band stretched on a wooden spool, 1 million hamsters on an exercise wheel, anything that makes something rotate that can be coupled up to the shaft of the induction machine.
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I have found it interesting to see the "terminology" that pops up from time and again such as " prime mover," in this case. Being familiar with gensets I was looking for where a gas/diesel engine comes into the picture.
That aside, I did sell (3) large 2300v auto transformer/reversing motor starter to AO Smth that control their largest truck frame presses. Their engineer required that I provide a "zero speed switch" that job was to detect movement of the motor being controlled after it was deenergized tha would not allow the motor to be reversed until basically at a stop.
Being that this was a unique application which involved questionable liability on our part I would not source the switch but requested that AO Smith supply the switch as well as showing me how they wanted it integrated into our control scheme.
The starters were delivered with a std ANSI 61 finish which the prompt response them orange installing hem up above the floor in a mezzanine. I did the start up showing them how it worked and it worked flawlessly.
 
junkhound said:
how can an induction motor generate kW without a prime mover

You sell the induction motor and buy a big pile of batteries and an inverter ? Nothing mechanical moving, so fits the definition ?

Akin to the famous physics test question: How do you find the height of a skyscraper with a barometer?

Ans: You knock on the building super's door, say: "hey, I'll give you this keen barometer if you tell me how tall the building is" !
Click to expand...
I like "You drop the barometer from the roof and measure the time it takes to hit the ground."
 
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