VSCOM is a non-linear impedance consisting of passive components
only - capacitors, reactors, resistors and non-linear resistors.
The circuit is designed in such a way that its impedance during
normal service condition is very low and is not affecting the network
impedance. In case of a phase-phase or phase-ground failure, which
is the normal cause of a voltage sag, the impedance of VSCOM will
increase and reduce the fault current to a low value thus eliminating
the voltage sag.