motor into a generator??
motor into a generator??
(OP)
Does anyone know if a typical 3 phase, 4 pole, induction motor that is rotated at 1500 rpm, can be used as a 3 phase generator producing nice sinusoidal waveform?
We would rotate this "generating" motor with another motor powered by a VFD. The equipment we are ultimately testing requires 50hz, 3 phase power. I'm sure we will have some issues to deal with regarding the output voltage level and efficiency of the system.
Our objective here is to build a 50hz generator from in-house surplus electrical pieces and 60hz service instead of renting the diesel units.
Thanks for your help. mikec56
We would rotate this "generating" motor with another motor powered by a VFD. The equipment we are ultimately testing requires 50hz, 3 phase power. I'm sure we will have some issues to deal with regarding the output voltage level and efficiency of the system.
Our objective here is to build a 50hz generator from in-house surplus electrical pieces and 60hz service instead of renting the diesel units.
Thanks for your help. mikec56





RE: motor into a generator??
Since you're apparently asking that your motor function as a stand-alone generator, I don't think this is going to work, since your motor have no source of excitation.
old field guy
RE: motor into a generator??
RE: motor into a generator??
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: motor into a generator??
The normal way to achieve those conditions is by connecting the induction machine to the 3-phase line ( exciter) and over-speed the rotor with the mechanical power source, returning electric power to the line. Only then, a capacitor bank connected in parallel could help to provide the required reactive power (excitation). If now, you disconnect that generator from the line voltage, the generated voltage will decay to a few volts (millivolts?) in a matter of seconds.
RE: motor into a generator??
RE: motor into a generator??
First time, induction motor driven over speed by a DC motor, with a load bank in parallel with the motor.
A watt meter confirmed that we were supplying power back to the line. The swith to the supply was opened leaving the motor, wattmeter and load bank islanded. The motor continued to supply real power to the load bank with no decay. There were no capacitors in the circuit.
Second try, The match of induction motor to DC motor was not good. The power available out of the DC motor was fairly small compared to the rating of the induction motor. We were not able to duplicate the results.
Many old textbooks stated that the motor contribution to a fault was for only a few cycles. Correct, but the reason that it is correct is that with a fault on the system being back fed by the induction motors, the motors are now induction generators supplying current to a fault. The energy extracted to supply the fault acts to quickly slow the motor to the point that the out put is negligible. That is, the reason for the fast decay is the fast decelleration of the motor rather than loss of excitation.
If the speed is maintained and a load is connected such that current continues to flow in the motor, many induction motors will continue to generate with no decay or litle decay of voltage. With capacitors in the circuit it is possible to maintain the voltage without decay and theoretically even see a rise in voltage when disconnected from the line.
respectfully
RE: motor into a generator??
How is the frequency sustained if the line reference is lost? . As far as I understand, an induction generator needs rotor speed slip from the synchronous field to generate, isn’t it?.
RE: motor into a generator??
It sounds like you wish to create a rotary frequency converter. This cannot be done by spinning a standard induction motor in the way you have described. A useful dscription of a rotary frequency converter can be found on Wiki: http://en.wikipedia.org/wiki/Rotary_converter
RE: motor into a generator??
RE: motor into a generator??
RE: motor into a generator??
Depending on the detailed requirements of this application, building an induction generator system from available components might be worth trying. Adding a sine filter to the output of an available VFD might be a better alternative.
RE: motor into a generator??
RE: motor into a generator??
1800 RPM corresponds to 60 Hz.
An induction motor at full load may run at 1750 RPM. That corresponds to 58.3 Hz. A drop of less than 3%.
The frequency does vary with loading, yes, but not much.
respectfully
RE: motor into a generator??
Please consider we are talking of a "generator" and what is desired is to create 50 HZ from 60 HZ power supply. A 4 poles machine should turn around 1.02x1500 rpm ~ 1530 rpm.
But if you do not have a reference line already with steady 50 HZ, how the induction generator will keep the 50 HZ adding only capacitors? Residual magnetism? That is for synchronous machines.
Mikec56. For nice sinus wave (and effective frequency and voltage control) use a "Brushless synchronous generator", rotating at 1500 rpm driven by your electric motor-VFD array. The voltage regulator will control the required field excitation (Voltage) and the VFD will keep the frequency (speed).
RE: motor into a generator??
The frequency depends on both the speed and the slip of both driving and driven motors. If you set the no-load speed 3% high you will get a frequency of about 3% low at full load.
The capacitors affect the voltage, not the frequency.
I agree with you completely that a synchronous generator is a much better solution.
The value of the time spent trying to get the system up and running with an induction generator will probably be more than the difference in price between a synchronous generator and an induction generator.
respectfully
RE: motor into a generator??
I am confused. VFD is the frequency coverter. Why can't you use the VFD as 50hz source? How nice the waveform has to be? What is being tested?
How big (HP/KVA)is the motor/generator requirement?
RE: motor into a generator??
I have been wondering that also. Thanks for asking.
respectfully
RE: motor into a generator??
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: motor into a generator??
I'd say that was why. Not everything likes having a PWM pseudo sine wave.
RE: motor into a generator??
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: motor into a generator??
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: motor into a generator??