ABB RET670 Applications Manual page 217

1MRK504116-UUS C
Application manual
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Figure 80: Thyristor switched series capacitor
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Figure 81: Thyristor controlled series capacitor
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I Current through the thyristor
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U Voltage over the series capacitor
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X Rated reactance of the series capacitor
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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 81. 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
82.
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Section 3
IED application
211