Hardware-In-The-Loop Testing and Analysis of Rapid Voltage Injection on Transmission Lines Using Modular SSSC with Line Distance Protection Security Considerations

Abstract ELES, ltd., is the combined transmission and distribution system operator of Slovenia. It operates 110 kV, 220 kV and 400 kV networks and has strong tie lines with transmission grids of Austria, Croatia, Hungary and Italy. As part of the ongoing efforts to ensure transmission system stability as well as operational flexibility under continuously changing conditions, advanced FACTS devices are being implemented into the grid. Installation of a Static Series Synchronous Compensator (SSSC) on a 220 kV interconnection line will help prevent internal bottle-necks and potential cascading events due to a loss of an interconnection line on the Slovenian – Austrian border. SSSC is a fast-acting device with rapid response capability for controlling power flow. Because local actions can quickly impact regional situations, it is essential to thoroughly consider all operational aspects during the feasibility assessment, design, and pre-engineering phases. This paper investigates the rapid voltage injection on a transmission line provided by a modular SSSC (m-SSSC) during a sudden increase in line currents. A case study for an m-SSSC with a rated reactive power of 80 MVAr per phase is considered. The adopted m-SSSC model was tested with electromagnetic transient (EMT) simulations. A sudden increase of the line currents corresponding to an N-2 event was simulated for various cases. The analysis of the m-SSSC responses shows the dynamic characteristics of the current override feature, which ensures rapid voltage injection. Special attention has been paid to the security of line distance protection operation, where hardware-in-the-loop simulation cases, with and without m-SSSC operation, have been considered. Two Siemens Siprotec 7SD5 numerical relays were tested using communication-assisted distance protection. The results show that the considered m-SSSC can prevent non-selective distance protection operation during such N-2 events.