Page 308 - Solutions Manual to accompany Electric Machinery Fundamentals

Appendix C: Salient Pole Theory of Synchronous Machines

C-1. A 13.8-kV, 50-MVA, 0.9-power-factor-lagging, 60-Hz, four-pole Y-connected synchronous generator
has a direct-axis reactance of 2.5 , a quadrature-axis reactance of 1.8 , and an armature resistance of
0.2 . Friction, windage, and stray losses may be assumed negligible. The generator’s open-circuit
characteristic is given by Figure P5-1.
Figure P4-1
(a) How much field current is required to make the terminal voltage V (or line voltage V L ) equal to 13.8
T
kV when the generator is running at no load?
(b) What is the internal generated voltage of this machine when it is operating at rated conditions? How
does this value of E A compare to that of Problem 4-2b?

(c) What fraction of this generator’s full-load power is due to the reluctance torque of the rotor?

SOLUTION

(a) If the no-load terminal voltage is 13.8 kV, the required field current can be read directly from the
open-circuit characteristic. It is 3.50 A.

(b) This generator is Y-connected, so I  I . At rated conditions, the line and phase current in this
L
A
generator is
P 50 MVA
I  A I  L   2092 A at an angle of –25.8
L 3  3 V V 13800

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