ABB Relion 670 series - Page 185

en06000595.vsd
Fw
Rv
-jX
C
Fw
Rv
-jX
C
Fw
Rv
-jX
C
IEC06000595 V1 EN
Figure 77: Thyristor switched series capacitor
en06000596_ansi.vsd
-
jX
C
Fw
Rv
jX
L
i
L
i
V
V
C
+ -
ANSI06000596 V1 EN
Figure 78: Thyristor controlled series capacitor
I
L
Line current
I
V
Current through the thyristor
U
C
Voltage over the series capacitor
X
C
Rated reactance of the series capacitor
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 78. 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 ground. 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
79.
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 179
Application manual