ABB RET670 Applications Manual page 211

1MRK504116-UUS C
Application manual
Steady state voltage regulation and increase of voltage collapse limit
A series capacitor is capable of compensating the voltage drop of the series inductance
in a transmission line, as shown in figure 71. During low loading, the system voltage
drop is lower and at the same time, the voltage drop on the series capacitor is lower.
When the loading increases and the voltage drop become larger, the contribution of the
series capacitor increases and therefore the system voltage at the receiving line end can
be regulated.
Series compensation also extends the region of voltage stability by reducing the
reactance of the line and consequently the SC is valuable for prevention of voltage
collapse. Figure 72 presents the voltage dependence at receiving bus B (as shown in
figure 71) on line loading and compensation degree K
equation 122. The effect of series compensation is in this particular case obvious and
self explanatory.
X
=
K C
C
X
Line
EQUATION1895 V1 EN
A typical 500 km long 500 kV line is considered with source impedance
=
Z 0
SA 1
EQUATION1896 V1 EN
A
Z
SA1
~
E
A
Seires
capacitor
IEC06000585 V1 EN
Figure 71: A simple radial power system
B
Power line
Load
en06000585.vsd
Section 3
IED application
, which is defined according to
C
(Equation 122)
(Equation 123)
205