The Effect of Sympathetic Inrush Current on the Protection Maloperation in the Capacitor Feeder at Shahroud 63kV Substation

Abstract

The energization of a power transformer, which is parallel to an operating power transformer, can cause an inrush current, called the sympathetic inrush current in the live power transformer. This current has high-frequency harmonic components as well as high values of decaying DC component. These can cause the saturation of the transformer core and the malfunction of some protection relays in the power system. These high-frequency currents in the capacitor bank reduce the capacitor reactance, so capacitors are always one of the sources of absorption of this type of current and the protection of the capacitor bank can be affected. In this paper, the effect of transformer sympathetic inrush current on protection relay maloperation in capacitor feeder is investigated. A case study has been presented for the outage of a capacitor bank at a 63kV substation in Shahroud during the power transformer energization. Simulation results in Digsilent software and event analysis are presented in this paper.