![background image](http://html1.mh-extra.com/html/abb/relion-670-series/relion-670-series_applications-manual_3052129165.webp)
en06000588.vsd
0
C
EA
A
ACC
A
DEC
A
SM
CR
P
Mech
P
Mech
P
[p
u
]
P
[p
u
]
with SC
without SC
A
ACC
A
DEC
A
SM
0
C
EA
CR
IEC06000588 V1 EN-US
Figure 84: Equal area criterion and first swing stability without and with series
compensation
This means that the system is stable if A
ACC
≤ (A
DEC
+ A
SM
). The stability margin is given by the
difference between the available decelerating energy (area between the P (δ) and P
Mech
and the
angular difference between δ
C
and δ
CR
) and the accelerating energy. It is represented in figure
by the area A
SM
. Notice that a substantial increase in the stability margin is obtained by
installing a series capacitor. The series compensation can improve the situation in two ways, it
can decrease the initial angle difference δ
0
corresponding to a certain power transfer and it
also shifts the P – δ curve upwards.
Improve reactive power balance
SEMOD168320-43 v2
A series capacitor increases its output of reactive power instantaneously, continuously and
automatically with increasing line load. It is thus a self-regulating device, which improves
voltage regulation and reduces the need for other means of voltage control for example, shunt
compensation. The reactive power balance of a series compensated line is shown in figure
as an example for 500 km long 500 kV transmission line with 50% compensation degree.
Capacitive
Inductive
200
400
600
800
1000
200
400
600
Q
(Mvar)
500
1000
1500
Power flow
(MW)
(T.L.)
(S.C.)
(T.L. + S.C.)
Transmission
Line
Series
Compensation
500 kV
500 km
k = 50 %
en06000589.vsd
IEC06000589 V1 EN-US
Figure 85: Self-regulating effect of reactive power balance
1MRK 505 343-UEN B
Section 7
Impedance protection
159
Application manual
Summary of Contents for Relion 670 series
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