Abstract
The European Union’s energy policy strives for a competitive, sustainable and secure energy supply in Europe. One of the most obvious results of this policy is the ongoing strong increase of energy from renewable, variable sources, determining the development of the transmission systems in the decades to come. In the next decades, a North-Sea grid interconnecting offshore wind farms will be built, which will gradually evolve into a European overlay grid connecting the offshore resources with the demand on the continent. The solar energy, concentrated in the south of Europe, will also require similar corridors to link them with demand. This so-called ‘super grid’ will form a new system of electricity highways throughout Europe.
Network elements based on power electronics are likely to play a major role in the future development of the super grid. They offer the possibility to control the power flows and increase the reliability of the network under variable working conditions. In particular high voltage direct current (HVDC) technology is the candidate for reinforcing and upgrading the transmission grids.
It is this given background back in 2013 which motivates the current project, the Impact of a possible Future European DC Super Grid onto the Actual AC Power System Protection Performance Project supported by the FCT Project with Reference EXPL/EEI-EEL/1940/2013. The general target of the project was to assess the impact on the normal operation of the actual power system protection. So that, European Transmission System Operators can advance measures to overcome possible challenges to this integration. Thus, this project intended to understand the risks of integrating VSC-HVDC in existing AC transmission grid, especially on the power system protection performance.
HVDC transmission systems have historically been connected to AC networks with high short-circuit power. This has meant that the AC Power protection has hardly been influenced by the HVDC transmission. With VSC-HVDC, the AC power system may no longer have a strong short circuit ration. As a result the possible impact of the HVDC transmission on AC line protection has to be considered. Thus, the aim of this work is to demonstrate the risk factors for improper AC line protection operation as well as the influence VSC-HVDC has on different types of line protections. The actual power system protection with the integration of a VSC-based HVDC was simulated using in a typical AC distribution network under different scenarios of operation: (1) normal network operation, (2) faulty network operation. The test was performed in real-time closed loop test with the help of the RTDS (Real-time Digital Simulator) and a commercial protective relay.
As a result of this assessment, developments on the actual protection scheme will be anticipated. The reliability of AC grid operation will be increased and the results might have an important positive impact on the power system industry.