SVC: Uses thyristor valves to rapidly add or remove shunt connected reactors and or capacitors often in coordination with mechanically controlled reactors and/or capacitors.

NGH-SSR DAMPER: a resonance damper, a thyristor ac-switch connected in series with a small inductor and resistor across the series capacitor.

STATCOM (static condenser): A 3-phase inverter that is driven from the voltage across a dc storage capacitor and whose output voltages are in phase with the ac system voltage. When the output voltages are higher or lower than the ac system voltage the current flow is caused to lead or lag and differences in voltage amplitudes determine how much current flows. Reactive power and its polarity can be controlled by controlling voltage.
PHASE ANGLE REGULATOR: The phase shift is accomplished by adding or subtracting a variable voltage concept that is perpendicular to the phase voltage of the line.

UNIFIED POWER CONTROL: In this concept, an ac voltage vector generated by a thyristor-based inverter is injected in series with phase voltage. The driving dc voltage for the inverter is obtained by rectifying the ac to dc from the same transmission line. In such an arrangement the injected voltage may have any phase angle relationship to the phase voltage. It is possible to obtain a net phase and amplitude voltage change that confers control of both active and reactive power.

DYNAMIC BRAKE: A shunt-connected resistive load, controlled by thyristor switches. such a load can be selectively applied in each pass, half cycle by half cycle to dampen any specific power flow oscillation so that generating unit runs less risk of losing synchronism, as a result, more can be transferred over systems subjected to stability constraints.

A thyristor-controlled resistor in parallel with the transmission line can be used effectively to damp power swing oscillations in the transmission system. FACT technology ensures power flow through prescribed routes, maximization of capacity, and securing loading capacity enhancement under various scenarios of uprating or upgrading the line’s thermal current capacity. One of the important functions of FACT is VAR compensation.

NGH- SSR DamperDamping of oscillation, series impedance control, transient stability
SVC-static var-compensatorVoltage control, var-compensation damping of the oscillation
TCSC-Thyristor controlled series capacitorPower control, voltage control, series impedance control, damping of oscillations, transient stability
Static-condenserVoltage control, VAR-compensator damping of oscillations, transient stability.
Thyristor-controlled phase angle regulatorPower control, voltage control, var-compensator, damping of oscillation, transient stability.
Thyristor-controlled dynamic brakeDamping of oscillation, transient stability.

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