Power quality enhancement by TCSC application to mitigate the impact of transformer inrush current

Excessive transient inrush current occurs during transformers energization, especially when the transformer core has remnant flux that adds to the flux build-up after switching. System voltage sag due to inrush current affects the power quality of the network in proximity of the transformer. The extent to which power quality is degraded depends on short circuit MVA at the source bus, and the magnitude and decay time constant of the transient current. This paper investigates the application of Thyristor Controlled Series Capacitor (TCSC) at the line ends to mitigate the impact of transformer inrush current on power quality. First, it describes the influence of TCSC on the short circuit MVA at the source bus, and then the mechanism by which the TCSC is able to mitigate voltage sags. It also investigates and illustrates different TCSC´s modes of operation on transformer inrush current. The ability of TCSC to limit fault currents by developing high inductive impedance under fault conditions with respect to transformer inrush current is also investigated.