Civil Engineering Reference
In-Depth Information
FIGURE 9-7
AC excitation system for synchronous generator.
scheme, the controlled DC voltage is obtained from a suitable stationary AC
source rectified and filtered. The DC voltage is then fed to the main field
winding through slip rings. This excitation scheme has a fast dynamic
response and is more reliable because it has no rotating exciters.
The excitation control system modeling for analytical studies must be care-
fully done as it forms a multiple feedback control system that can become
unstable. The IEEE has developed industry standards for modeling the exci-
tation systems. The model enters nonlinearly due to magnetic saturation
present in all practical designs. The stability can be improved by supplement-
ing the main control signal by auxiliary signals such as speed and power.
9.3.3
Electrical Power Output
The electrical power output of the synchronous machine is as follows:
PVI
=
cos
φ
(9-3)
Using the phasor diagram of
Figure 9-6
,
the current can be expressed as
follows:
(
)
−
E
cos
δ
+
j
sin
δ
V
EV
jXs
−
=
∠−∠
=
EVo
jXs
δ
I
=
(9-4)
jXs
E
⋅
sin
δ
.
The real part of this current is
I
=
real
X
s
This part, when multiplied with the terminal voltage V gives the output
power:
VE
Xs
P
=
sin
δ
(9-5)
