EE320 Homework # 9
Synchronous Machines
SOLUTION
Problem 1: A 4-pole, 60Hz, Y-connected, 3-phase generator has a regulated terminal line-to-neutral
voltage of Vas
and
= 260Vr ms ∠0 , a synchronous reactance of 0.06Ω , a stator resistance of 0.003Ω ,
Lsf = 0.02H . The balanced 3-phase load draws 2MW at a lagging 0.8 power factor.
a.
b.
c.
d.
e.
Compute the 3-phase complex power of the load (magnitude and angle)
Compute the generator phase current (magnitude and angle; hint: the angle of the current should
be negative for the load to have a lagging power factor)
Find the required excitation voltage ( E a )
Calculate the required field current
Calculate the required speed of the prime mover
Problem 2: Given the same machine as in problem 13.1. If the excitation voltage is
E a = 360Vrms∠14
and the field current is adjusted to maintain the same terminal voltage as in Problem 13.1,
a.
b.
c.
Find the new generator phase current
Calculate the 3-phase real power consumed by the load and identify the new power factor
Calculate the generator efficiency (consider stator winding losses as the only losses)
Problem 3: A 3-phase, Y-connected, 6-pole, 60Hz generator has
resistance), and
Lsf = 0.2H . The machine operates at a power angle of 31.48  with a field current of
100A. The line-to-neutral terminal voltage is 2400Vrms.
a.
b.
c.
d.
e.
X S = 1Ω , negligible rS (stator
Find the speed of the prime mover in rad/sec
Determine the excitation voltage
Find the line current
Find the power consumed by the load and its power factor
Find the developed torque
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