ABB RELION 670 Series Applications Manual page 168

Section 7
Impedance protection
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IEC06000595 V1 EN-US
Figure 75: Thyristor switched series capacitor
I
L
IEC06000596 V1 EN-US
Figure 76: Thyristor controlled series capacitor
I Line current
L
I Current through the thyristor
V
U Voltage over the series capacitor
C
X Rated reactance of the series capacitor
C
A thyristor controlled series capacitor (TCSC) allows continuous control of the series capacitor
reactance. This is achieved by adding current through the capacitor via the parallel thyristor
valve path see figure 76. The main circuit of the TCSC consists of a capacitor bank and a
thyristor controlled inductive branch connected in parallel. The capacitor bank may have a
value of for example, 10...30 Ω/phase and a rated continuous current of 1500...3000 A. The
capacitor bank for each phase is mounted on a platform providing full insulation towards
earth. The thyristor valve contains a string of series connected high power thyristors with a
maximum total blocking voltage in the range of hundreds of kV. The inductor is an air-core
reactor with a few mH inductance. The wave forms of a TCSC in capacitive boost mode are
shown in figure 77.
I
L
I
V
U
C
X
C
IEC06000597 V1 EN-US
Figure 77:
162
-jX -jX
C C C
Fw Fw Fw
Rv Rv
en06000595.vsd
-jX
C
+ -
UC
F
W
jX
L
R
v
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2 2
0 0
-2 -2
0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08
5 5
0 0
-5 -5
0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08
50 50
0 0
-50 -50
0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08
0 0
-20 -20
-40 -40
0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08
TCSC wave forms presented in capacitive boost mode for a typical 50Hz
system
0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 0.18 0.18 0.2 0.2
0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 0.18 0.18 0.2 0.2
0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 0.18 0.18 0.2 0.2
0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 0.18 0.18 0.2 0.2
en06000597.vsd
1MRK 504 152-UEN B
Application manual