Page 262 - Solutions Manual to accompany Electric Machinery Fundamentals

The rated current of this generated is 50 A, so 40 A is 80% 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 240 Aturns. The demagnetizing effect of armature reaction is equivalent to a
reduction in field current of


240 A t
I    0.24 A
F
1000 t
The figure below shows that a triangle consisting of 7.2 V and (240 Aturns)/(1000 turns) = 0.24 A fits
exactly between the E A and V T lines at a terminal voltage of 105 V.

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