How Does Power Factor Change with Field Induced EMF in a Synchronous Motor?

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SUMMARY

The discussion focuses on calculating the power factor of a star-connected, 3-phase synchronous motor rated at 100kVA, 415V, and 50Hz, with a synchronous reactance of 1.2 ohms and a per-phase field-induced EMF of 228V. The calculated power factor is 0.89, and the new value of the field-induced EMF, after adjusting the excitation to change the sign of the reactive power, is determined to be 365V. Key equations utilized include the complex power formula and the relationship between line current, phase voltage, and synchronous reactance.

PREREQUISITES
  • Understanding of synchronous motor operation and characteristics
  • Familiarity with complex power calculations in electrical engineering
  • Knowledge of synchronous reactance and its impact on power factor
  • Proficiency in using phasor diagrams for AC circuit analysis
NEXT STEPS
  • Study synchronous motor performance characteristics and efficiency
  • Learn about the effects of excitation on synchronous motor operation
  • Explore the relationship between power factor and reactive power in AC circuits
  • Investigate advanced power factor correction techniques for synchronous motors
USEFUL FOR

Electrical engineers, students studying motor control, and professionals involved in power systems and motor performance optimization will benefit from this discussion.

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Homework Statement



A star-connected, 3-phase, 100kVA, 415V, 50Hz synchronous motor having a synchronous reactance of 1.2ohms and negligible resistance operates at its rated terminal voltage, rated current and per-phase field-induced emf of 228V. Determine the power factor.

The excitation is adjusted until the numerical value of the power factor is the same as initially but the sign of the reactive power is changed. Determine the new value of field induced emf.

Homework Equations



Power = 3 Vp.Ip.PF.

Complex Power = Vl.Il/root3

V = Ef + jIaXs

Vl = Vp. root 3

Complex Power = S = P + jQ

The Attempt at a Solution



I calculated the following(correctly, I think):

The synchronous angular velocity is 100.pi rad/s.

The line current is 46.37 Amps

IaXs = 55.65V

Phase Voltage = 239.6V

I can't seem to find the power factor though.




The answers are PF = 0.89, New value of field induced emf = 365V


As always any help would be greatly appreciated. Thank you
 
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Hi Guys,

Been thinking about the problem a lot and I still can't figure out an answer to this problem.

If somebody could please help me with this I would be extremely grateful.

Thanks.
 

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