Electronics > Beginners
more synchronous motor questions that make no sense
(1/1)
Simon:
--- Quote ---(i) A star-connected, three-phase synchronous induction motor takes
a current of 10 amps from a 415 volt supply at unity power factor
when supplying a steady load. If the synchronous reactance is
5 ohms/phase and the resistance is negligible, draw the phasor
diagram and calculate the value of the generated emf and the load
angle.
(ii) If the excitation is reduced by 10% and, as a consequence the
generated e.m.f. is reduced by 10%, calculate the new value of the
generated e.m.f E, the stator current, the power factor and the load
angle, assuming that the load does not change.
(iii) Comment very briefly on the effect that reducing the excitation has
on the power factor, stator current and the load angle,
--- End quote ---
So how can (ii) be calculated? sure the new emf is now 90% so how can there be both an unknown PF and stator current draw? one determines the other ?
Simon:
My take is that if i assume no load angle change i can calculate the new IXs vector and it's angle, but as load angle will influence the IXs angle and therefore the power factor one needs to be known. Can I make the assumption that given the exitation is reduced by 10% the load angle shifts by 10% as maybe the torque is now 90% of what it was?
Simon:
Or given the attached i could indeed calculate the new current and it's angle or the angle of the E vector
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