induction motor to generator 1

[bendover]

i have a problem with an induction motor come generator, the unit is engine driven,it flashes a small dc voltage into the winding every time the engine is run,the motor is used as a motor when hooked up to the mains,but when driven by the engine is used to power heater bars in a fridge unit,can any one tell me what exactly allows this motor to generate power,assuming the dc voltage excites the motor and three capacitors are used for smoothing the generated voltage,the unit in particular in question will not generate, the capacitors are all good and dc voltage is being injected into the motor winding. Any information to this problem greatly received.

 

[Lewish]

I hope when you say induction motor that you mean asynchronous. Going with that, then the capacitors are an important part of the excitation circuit when the motor becomes a generator. When an asyncronous motor is turned at any speed lower than it synchronous speed, (i.e., the rpm on the nameplate) and up to the speed that would be synchronous for a synchonous motor, (ex. 1800rpm for a 4 pole motor) it can not function as a generator. Once you cross that synchonous motor speed, say 1800rpm for this example, then the capacitors (if they are correctly sized) will supply the excitation current for generation. So, let's say you have a 1750rpm asynchronous motor, when you turn it at 1850rpm, it will generate the amount of power that it would consume as a motor. The only reason for the DC voltage is to ensure that there is some residual magnetic field to get everything going.

So, with all of that said, if the capacitors are correct, then I suspect that your problem is the motor isn't being turned fast enough to be a generator.

I hope this helps.

Lewis

 

[jbartos]

Suggestion: Visit

http://stat.tamu.edu/doc/matlab65/toolbox/powersys/tut_ch20.html

for:
As the simulation starts, you will notice that the three ASM currents start from 0 and contain a slowly decaying DC component.

 

[bendover]

Hi lewish thanks for the info, what has actually happened was the motor that was in the unit had a cracked casting so we obtained a new motor, the original motor had 9 termination studs and the new one only 6,the motor is wired in star, the capacitors are 23 microfarad and i have checked they are ok the engine speeds have to be set correctly as advised by the manufacturer because the whole unit is driven via a centrifugal clutch so i don`t think speed is the problem, from what you are saying i think there is a fault in the capacitor circuit somewhere any further info would be good, i think it is a leroy sommers motor, on mains operation the f.l.a is about 27 per phase.