New control strategies to prevent blackouts: Intentional islanding operation in distribution networks

Several countries have experienced electric system deregulation. The market deregulation is currently associated with deep changes in distributed resources (DR or DG) technologies and communication & information technologies (ICT). The massive connection of DR and the need to improve their profitability leads to new electric system management concepts. The article presents the possible use of DR to supply partially local distribution area, isolated from the interconnected electrical power system (EPS) during a blackout for instance. This technical capacity may be achieved at various scales and may last several hours during a restoration process following a blackout. This intentional islanding may result of an ultimate saving action for a specific area of the EPS, or of a black start in a local area. This specific EPS running mode leads to new kind of DR control and DNO operation tools, to a new fast adaptation of the local protection systems. Some existing areas in the distribution EPS may be relatively well adapted to manage the needed local agent. The size and the location of these possible cells are introduced in the paper. The typical voltage level targeted in the paper is the medium voltage (MV). The main interest is to take profit of a local production capacity (interest for the network operator, the consumer and the producer) to increase the local security and availability. But this profit has a cost: local control and protection reinforcement and real time adaptation. This paper gives information on some local area networks characteristics: possible topology flexibility, cell definition, need for a specific exploitation strategy (frequency and voltage control requirement), improvement needed for the protection system and for the local information system. The intentional islanding availability study is presented in the paper through a proposed methodology that may be automated in the long run. The approach proposed in this paper is essentially based- on technical constraints. The methodology is applied to a study case and the results are illustrated using EUROSTAG software simulation. Finally, a few characteristics for the information system for the intentional islanding application are given. The works included in the article are integrated in the CRISP project (CRISP: Distributed Intelligence in Critical Infrastructures for Sustainable Power. Project funded by the European Community under the Fifth RTD Framework Program (2002–2005)).