TCSCs

Thyristor-Controlled Series Capacitor (TCSC) is a type of flexible AC transmission system (FACTS) device used in electrical power networks to control power flow and improve dynamic performance of transmission lines. It achieves this by presenting a controllable reactance in series with the line, thereby affecting the impedance seen by power flowing along the path.

In common configurations, a fixed capacitor bank is placed in series with the transmission line, and a thyristor-controlled reactor (TCR) is connected in parallel with the capacitor. By adjusting the firing angle of thyristors in the TCR, the reactive current absorbed or supplied by the parallel circuit is changed, producing a continuously variable net reactance as seen by the line. This arrangement can also include harmonic filtering and protection elements to manage switching harmonics and ensure reliable operation.

Control of a TCSC relies on a dedicated control system that uses measurements of voltage, current, and phase angle to determine the desired impedance. The objective is to steer power flow, enhance transient stability, damp power swings, mitigate subsynchronous resonance, reduce congestion, or optimize losses. The device responds rapidly to changing conditions, providing fast-acting impedance variation without mechanical moving parts.

Applications of TCSCs include long-distance transmission corridors and network segments requiring dynamic congestion management and stability improvement. Advantages include fast response and no moving parts, while limitations involve harmonic distortion from switching, need for filtering and protection coordination, and higher installation costs relative to fixed-series compensation. See also FACTS, SSSC, SVC, UPFC, STATCOM.