Distributed Generation and Reclosing Coordination

Distribution networks have traditionally been designed for unidirectional power flow. Large scale implementation of distributed generation (DG) means that this fundamental assumption is not true any more. This causes several challenges to network design and operation. One of the most critical affected areas is system protection. The impact of DG on protection has been examined in several research papers during the last years. The most challenging issue seems to be anti-islanding protection, especially when automatic reclosing is applied. In this paper, the effect of DG on automatic reclosing is studied. After a short literature review, the method and results of simulation studies are presented. The simulations verify the existence of the problems. Protection requirements and possible solutions are discussed. Because of speed and reliability requirements, telecommunication based protection seems to be the most suitable solution, when the share of DG becomes significant. IMPORTANCE OF AUTOMATIC RECLOSING In medium voltage overhead networks all over the world automatic reclosing is widely used and a very effective method of fault clearing. According to [1], 70-95% of the faults are temporary. Figure 1 illustrates the importance of automatic reclosing according to a Finnish study [2]. Figure 1. Share of different faults and fault clearing by automatic reclosing in Finnish overhead networks [2].