Effects of SSSC on Distance Relay Tripping Characteristic

This paper presents the measured impedance at the relaying point in the presence of one of the series connected flexible alternating current transmission system (FACTS) devices, i.e. static synchronous series compensator (SSSC). The presence of SSSC on a transmission line greatly influences the tripping characteristic of distance relays. Distance relay tripping characteristic itself depends on the power system structural conditions (short circuit levels at the line ends), pre-fault loading (load angle and voltage magnitude ratio of the line ends), and especially the ground fault resistance. In the presence of SSSC, its controlling parameters as well as its connection point also affect the tripping characteristic. Here, the measured impedance at the relaying point is calculated due to the mentioned affecting parameters.

I. Introduction

THE distance protection operation is based on the measured impedance at the relaying point. There are several factors affecting the measured impedance at the relaying point. Some of these factors are related to the power system parameters prior to the fault instance [1] [3], which can be categorized into two groups. First group is the structural conditions, represented by the short circuit levels at the transmission line ends, whereas the second group is the operational conditions, represented by the line load angle and the voltage magnitude ratio at the line ends. In addition to the power system parameters, the fault resistance could greatly influence the measured impedance, in such a way that when the fault resistance is equal to zero, the power system parameters do not affect the measured impedance. In other words, power system parameters affect the measured impedance only in the presence of the fault resistance, and as the fault resistance increases, the impact of power system parameters becomes more severe.