Page 542 - Industrial Power Engineering and Applications Handbook

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I \ \ \
G2 slower G1 faster \

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v, = €2 + lc ' 22
. I I
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. .. I I I
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Motoring action Generating action .:/E2 I
I
I
I
Note Magnitude of iEl and E2 remains unchanged
* EC is not appearing at 90" with lc because of lc . R, which is negligible but we
have considered it to be significant for better illustration
Figure 16.16(a) Effect of increasing the driving torque on no-load (magnified representation)
Zl z2
operate as a generator and G2 as a synchronous motor
and
b € C _I
Figure 16.16(b) Residual voltage across the internal
circuit of generators GI and G2 If z, z,
=
E{ +E,
circuit of the two generators. The only difference would (16.7)
then V, = ~ 2
be that now they will be in phase but different in
magnitudes, i.e.
B Performance on-load
E; -E? = E, 1 By changing the driving torque or power input
The performance of two or more generators, running
I, = E, in parallel, on-load is not very different than analysed
ZI + 22 on no-load. A generator running in advance compared
I, will lag E, by almost 90' and lead E, by almost 90" to the others would share a higher load than those
(Figure 16.17). The net effect will be a demagnetizing running behind. The performance can be analysed
armature reaction for GI, tending to weaken its field more easily by referring to Figure 16.16(a).
and diminish E;, whereas for G2 it would be a For more clarily, consider any of the two generators
magnetizing armature reaction, tending to strengthen to be identical and running at the same speed,
its field and enhance E2. Both machines would thus generating the same voltage and sharing an equal load
tend to synchronize once again. GI will now also of, I at a lagging p.f. cos $, i.e.

G2 -Synchronous motor G1 - Generator