Page 120 - Solutions Manual to accompany Electric Machinery Fundamentals

(c) If armature resistance is ignored, the internal generated voltage E A will increase as flux increases,
but the quantity E A sin  will remain constant. Therefore, the voltage for any flux can be found from the
expression

  
E    E  Ar

A
  r 
and the angle  for any E A can be found from the expression

 E 
  sin 1  Ar sin  r 


 E A 
where  is the flux in the machine,  is the flux at rated conditions, E Ar is the magnitude of the internal
r
generated voltage at rated conditions, and  is the angle of the internal generated voltage at rated
r
conditions. From this information, we can calculate I A for any given load from equation

E  V
I  A 
A
jX S
and the resulting reactive power from the equation
Q  3 I A sin 
V

where  is the impedance angle, which is the negative of the current angle.
The rated line and armature current for this generator is
S 500 kVA
I  I    90.2 A
L
A
3 3  V 3200 V
T

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