Page 261 - Solutions Manual to accompany Electric Machinery Fundamentals

(c) The rated current of this generator is 50 A, so 20 A is 40% of full load. If the full load armature
reaction is 300 Aturns, and if the armature reaction is assumed to change linearly with armature current,
then the armature reaction will be 120 Aturns. The demagnetizing effect of armature reaction is
equivalent to a reduction in field current of


120 A t
I    0.12 A
F
1000 t
The figure below shows that a triangle consisting of 3.6 V and (120 Aturns)/(1000 turns) = 0.12 A fits
exactly between the E A and V T lines at a terminal voltage of 114 V.

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