Voltage correspond to min. speed

[karis]

Hi all,

This is just my first time. I had a chance to check out some of the question and answer and find it very help full.

This is the situation. I have been asked to find the voltage correspond to the minimum speed permanent magnet generator. The generator is 75 kw, 3 ph, 0.8 PF and it is using variable speed engine as a prime mover. This generator is supposed run a motor (40 HP, 460/3Ph/60Hz) and my supervisor is interested to know the current drawn when the voltage out put is minimum which is correspond to the minim speed of the generator. I contacted the generator manufacturer but they need to know what s/n of the generator which I am waiting to get in couple of days.

So I was wondering if any of you guys can give me some guidelines in this situation.

Thanks and appreciate all your comment.

K.

 

[winnie]

For a rough approximation, the output voltage will be proportional to speed. This ignores things like armature reaction and the current versus voltage characteristics of the load. The output frequency will be proportional to speed.

For the motor, presuming an induction motor, the proper operating voltage will be proportional to the supplied frequency. If you maintain constant V/Hz, then the magnetizing current and magnetic flux will remain roughly constant. If the mechanical load has constant torque, then I would expect the torque producing current to remain constant.

Thus as a rough guess, I would expect that as your prime mover changes speed, the voltage, frequency, total power, and output speed of the motor will all drop, but the line current between generator and motor would remain roughly constant.

This is just a rough guess based upon an insufficient description of your system.

-Jon