Reliable detection of electrical islands. Base for a cellular grid operation mode.

• Applicant: Professor Dr.-Ing. Peter Schegner
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 266767012

Distributed generation units (DG) are integrated in the public electrical grid each year. DGs, which use renewable energy sources, are especially supported. Therefore, many large-scale power plants, which are operated by fossil energy sources, are becoming unprofitable and have to be closed down. The generation of active power as well as many essential system services like reactive power supply, control reserve and maintenance of power quality have to be taken over by smaller DGs. Thereby, the character of the electrical grid changes from a centrally organized to a decentral system with distributed control tasks. This conversion of the public electrical grid causes an increasing frequency of unintentional electrical islands, which can lead to uncontrolled, and therefore potentially dangerous, continued energy supply. An unintentional island is a sub-grid, which stays energized after disconnection from the upstream grid, even if a de-energized state was the purpose of the disconnection.Previous investigations show that a lot of research in the field of unintentional islands has still to be done. On the one hand, fundamental investigations on the transition processes from integrated grid to electrical island and backwards have to be executed. On the other hand, interactions between different DGs have to be considered. The RLC parallel circuit, which was assumed as worst-case load condition so far, proved to be uncritical in comparison to the real electrical load in the grid. The previous assumption, that an investigation of DG behavior with RLC-loads is sufficient could be refuted. The load behavior of low-voltage grids could be determined and analyzed in the project so far. In the next step, it is important to extend the investigation to medium-voltage distribution grids and measurements with 3 phase inverters. The occurrence of unintentional islands in various actual distribution grids in the last years confirms that the problem is already relevant. At the same time, basic knowledge and experience in handling of this phenomenon are lacking.The approach of distributed generation of energy, which is pursued by the continuing integra-tion of DGs, has the potential of a safe energy supply of sub-grids even during outages of the upstream grid. To make this possible, concepts for the operation of intentional islands in the framework of a cellular grid operation mode have to be integrated early during the reorgani-zation of the electrical system. Therefore, in this project the possibility to utilize electrical storages and concepts for a selective adjustment of electrical loads in an intentional island shall be investigated. This extended islanding concept has to ensure a continued energy supply of large sub-grids in case of potential major outages. An intelligent control of the sub-grids, which enables a safe resynchronization to the upstream grid without outage times, will be designed.

• DFG Programme: Research Grants