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Synchronous Machine Voltage Curves & Torque Relation to Armature Current

  1. Mar 31, 2017 #1
    Hello everyone

    Im new on the forum and I just discovered what are sync machines...

    I have really basic question what I still cannot figure out.. I did some experiments with motor for different field currents and torques. In the result I measured armature currents and did V curves. But next question asks to do find theoretical solution for same problem. As I guess, torque related to the power through sync speed and power related to I armature as I=P/(Va*cos(theta)). However it doesnt work for me and Im pretty lost.

    Maybe someone can give me at least direction where and what I should read about.. I have air gap voltages, open and short circuit charachteristics and different input torques and calculated different sync inductance values for open loop voltages. Machine is 400v 0.8kW cos=0.75 50Hz 4 poles 1500rpm.
     
  2. jcsd
  3. Mar 31, 2017 #2
    Get a good book on electrical machine theory. I recommend the ones authored by Krause (Purdue U).
     
  4. Apr 1, 2017 #3

    jim hardy

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    Gold Member

    The way to think about synchronous motors is an electromagnet in motion being dragged along by the magnetic field of stator ..
    A generator is identical except torque is reversed, rotor is held back by stator.

    From that mental picture it's a small step to phasor representation of what's going on. Brush up your grade school geometry and dust off your old drafting compass...

    We've had a lot of threads on synchronous machines
    see if this one is any help.
    https://www.physicsforums.com/threads/voltage-and-reactive-power-relationship.876346/#post-5503690
     
  5. Apr 1, 2017 #4
    The one thing that I would add to Jim's answer is that the magnetic pole on the rotor is always locked to the corresponding pole on the stator; it is not allowed to slip. If the torque is so great that it does slip, the machine falls out of synchronism.
     
  6. Apr 3, 2017 #5
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