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problem1) The three-phase 50 Hz synchronous generator is operating at unity power factor, with following conditions: line-line voltage 13kV, stator current 1000A, field current 80A, torque angle 20°

a) Determine:

i) magnitude of the induced voltage E, and

ii) value of the synchronous inductance Ls

b) It is now desired to supply 8MVARs (lagging) while maintaining the similar real power as above. Sketch the phasor diagram showing E, V, and I for this case, and determine numerical values for

i) the new field current, and

ii) the new torque angle δ.

problem 2) Estimate the value of the distribution factor for three-phase alternator having 12slots/pole. [0.958]

problem3) The three-phase winding is housed in 3 slots/pole/phase. Two slots cord the winding. Estimate the coil span factor for:

a) The fundamental [0.939]

b) The 3rd harmonic [0.5]

c) The 6th harmonic [-0.5]

problem4) Find out the regulation of the three-phase, star-connected, 500-kVA, 3300-V, alternator for power-factors of 1, 0.8 lagging and 0.8 leading. The synchronous reactance is 4 ! and the resistance is 0.7 !. [4.84% ; 14.37% ; -6.95%]

Theory problems

problem1) Does change in excitation affect synchronous motor speed?

problem2) Does change in excitation affect the power factor?

problem3) How does excitation affect power factor?

problem4) For what service are synchronous motors especially suited?

problem5) Which has more efficiency; synchronous or induction motor?

problem6) Mention some specific applications of synchronous motor?

problem7) What is the synchronous capacitor?

problem8) What are the causes of faulty starting of a synchronous motor?

problem9) What could be the reasons if a synchronous motor fails to start?

problem10) A synchronous motor starts as usual but fails to develop its full torque. What could it be due to?

Electrical & Electronics, Engineering

  • Category:- Electrical & Electronics
  • Reference No.:- M9579

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