ABB REL670 2.2 IEC - Page 174

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IEC06000596 V1 EN-US
Figure 76: Thyristor controlled series capacitor
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Current through the thyristor
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Voltage over the series capacitor
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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 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
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IEC06000597 V1 EN-US
Figure 77: TCSC wave forms presented in capacitive boost mode for a typical
50Hz system
The apparent impedance of the TCSC (the impedance seen by the power system)
can typically be increased to up to 3 times the physical impedance of the capacitor,
Section 8 1MRK 506 369-UEN B
Impedance protection
168 Line distance protection REL670 2.2 IEC
Application manual