Thyristor and Gate-Controlled Series Capacitors: A Comparison of Components Rating

The thyristor-controlled series capacitor (TCSC) is a commercially available flexible AC transmission system (FACTS) device developed for controlled compensation of transmission-line impedance, which consequently leads to the control of transmission-line power flow. The gate-controlled series capacitor (GCSC), a FACTS device based on a pair of gate-commutated switches in parallel with a capacitor, can also control impedance and power flow of transmission lines. Here, it is shown that in many situations where a controllable series compensator must be installed, the GCSC may be used instead of the TCSC, possibly with some advantages. A comparison of the sizing of the TCSC and the GCSC components is presented. It is shown that the capacitor in the GCSC can have lower megavolt-amperes than in the TCSC, especially for power-flow control applications. Also, it is shown that the thyristor valve in the TCSC needs to have a higher current rating than the gate-commutated switch valve in the GCSC.