Page 788 - Basic Electrical Engineering

Figure 10.17 (a) Effect of change of excitation; (b) effect of change of prime-mover input

Let us increase the excitation current so that the induced EMF is increased

from E ′ to E ″ as has been shown in Fig. 10.17 (a). A resultant voltage equal
i
i
to E ″ – V = E will appear which will circulate current I between the
i
c
R
B
incoming alternator and the existing one. I will lag E because the reactance
c
R
of the alternators is very high as compared to their resistances. The effect of
I will be to reduce the reactive component of the load current so that the load
c
current will change from I to I ′. Thus, it is seen that change of excitation
L
L
current of the incoming generator will only cause reactive load sharing but
not active load sharing. Change of excitation of the incoming machine will

only change the reactive power delivered by the existing machines.

(b) Effect of change of prime-mover input