ABB Relion 670 series, Руководство по применению

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en06000586.vsd
0 200 400 600 800 1000 1200 1400 1600 1800
100
200
300
400
500
P[MW]
U
[k
V
]
U
limit
P
0
P
3
0
P
5
0
P
7
0
IEC06000586 V1 EN-US
Figure 82: Voltage profile for a simple radial power line with 0, 30, 50 and 70% of
compensation
Increased power transfer capability by raising the first swing stability limit
SEMOD168320-32 v2
Consider the simple one-machine and infinite bus system shown in figure 83 .
en06000587.vsd
~
E
A
Z
SA1
A B
P
Mech
+jX
Line
-jX
C
System
IEC06000587 V1 EN-US
Figure 83: One machine and infinite bus system
The equal-areas criterion is used to show the effectiveness of a series capacitor for
improvement of first swing transient stability (as shown in figure 84 ).
In steady state, the mechanical input power to the generator (P
Mech
) is equal to the electrical
output power from the generator (P
E
) and the generator angle is d
0
. If a 3-phase fault occurs
at a point near the machine, the electrical output of the generator reduces to zero. This means
that the speed of the generator increases and the angle difference between the generator and
the infinite bus increases during the fault. At the time of fault clearing, the angle difference has
increased to δ
C
. After reclosing of the system, the transmitted power exceeds the mechanical
input power and the generator deaccelerates. The generator decelerates as long as equal area
condition A
ACC
=A
DEC
has not been fulfilled. The critical condition for post-fault system stability
is that the angular displacement after fault clearing and during the deceleration does not
exceed its critical limit δ
CR
, because if it does, the system cannot get back to equilibrium and
the synchronism is lost. The first swing stability and the stability margin can be evaluated by
studying the different areas in figure 84 for the same system, once without SC and once with
series compensation. The areas under the corresponding P – δ curves correspond to energy
and the system remains stable if the accelerating energy that the generator picks up during
the fault is lower than the decelerating energy that is transferred across the transmission line
during the first system swing upon fault clearing.
Section 7 1MRK 505 343-UEN B
Impedance protection
158
Application manual