In large systems with many generators connected in parallel, it may be necessary to use a series reactor to prevent excessively large current flow during a short circuit; this protects transmission line conductors and switching apparatus from damage due to high currents and forces produced during a short circuit.
[1] The utility of shunt reactors for voltage control on lightly-loaded transmission lines was examined in a 1926 paper presented at the AIEE by Edith Clarke.
[2] For short lines, we can basically ignore the impact of capacitive current from a voltage regulation point of view, but medium and long lines can have voltages at their receiving end much higher than the sending end, thus creating issues such as over-fluxing of power transformers and over stressing of line insulators.
In case of regulated DC voltage source connection to the control windings, biasing flow is increasing and directed to different sides in the adjacent cores.
Change in biasing current value leads to the power winding current change, due to which a stepless variation of voltage levels in CSR connection point as well as the value of reactive power consumed by the reactor is ensured.