ABB RELION RET670, Applications Manual

Page: 212 / 1016

Steady state voltage regulation and increase of voltage collapse limit
SEMOD168320-24 v2
A series capacitor is capable of compensating the voltage drop of the series inductance
in a transmission line, as shown in figure
79 . 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
80 presents the voltage dependence at receiving bus B (as shown in
figure 79 ) on line loading and compensation degree K
C
, which is defined according to
equation 53 . The effect of series compensation is in this particular case obvious and
self explanatory.
=
C
C
Line
X
K
X
EQUATION1895 V1 EN-US
(Equation 53)
A typical 500 km long 500 kV line is considered with source impedance
1
0
=
SA
Z
EQUATION1896 V1 EN-US
(Equation 54)
~
E
A
Z
SA1
Power line
A B
Seires
capacitor
Load
en06000585.vsd
IEC06000585 V1 EN-US
Figure 79: A simple radial power system
Section 8
1MRK 504 163-UUS A
Impedance protection
206 Transformer protection RET670 2.2 ANSI
Application manual