+
E
-
I, (P, Q)
j X
d
j X
net
+
V
-
+
E
net
-
en06000321.vsd
IEC06000321 V1 EN-US
Figure 145: A generator connected to a power system, represented by an
equivalent single phase circuit
where:
E represents the internal voltage in the generator,
X
d
is the stationary reactance of the generator,
X
net
is an equivalent reactance representing the external power system and
E
net
is an infinite voltage source representing the lumped sum of the generators in the system.
The active power out from the generator can be formulated according to equation
161:
EQUATION1540 V1 EN-US (Equation 161)
where:
The angle δ is the phase angle difference between the voltages E and E
net
.
If the excitation of the generator is decreased (loss of field), the voltage E becomes
low. In order to maintain the active power output the angle δ must be increased. It is
obvious that the maximum power is achieved at 90°. If the active power cannot be
reached at 90º static stability cannot be maintained.
The complex apparent power from the generator, at different angles δ is shown in
figure 146. The line corresponding to 90° is the steady state stability limit. It must be
noticed that the power limitations shown below is highly dependent on the network
impedance.
1MRK 502 071-UUS A Section 8
Impedance protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 303
Application manual
To Next Page
Loading...
