Circuits

Q.2 (20 marks) A 2XY-hp, 6 XY-V, 0.85-PF-leading A-connected synchronous motor has an armature resistance of 0.2 Q and a synchronous reactance of 3.7 Q. Its efficiency at full load is 92%. The field current flowing under these conditions is 3.5 A. (where XY are the last two digits of your student ID).

a)What is the input power to the motor at the rated conditions? (2 marks)

b)What are the line and phase currents of the motor at rated conditions and pf? (2 marks)

c) What is the reactive power consumed by or supplied by the motor at rated conditions?(2 marks)

d)What is the internal voltage Ea of this motor at rated conditions? (2 marks)

e)What the converted power and induced torque at rated conditions? (2 marks)

f)If Ea is decreased by 10 percent, how much reactive power will be consumed by or supplied by the motor? (2 marks)

g)How much field current would be required to make the motor operate at 0.85 PF leading? (current magnitude might not necessarily remain the same). (2 marks)

h)If the load on the motor is decreased by 20% of the rated power while the motor operates at unity power factor, what will be the new torque angle? (3 marks)

If the field current was increased by 10 percent, what would the new value of the armature current be? What would the new power factor be? How much reactive power is being consumed or supplied by the motor? (3 marks)

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