Two Years of Battery Energy Storage System performance in automatic islanding in the Portuguese MV network

Abstract

Energy Storage Systems (ESS) have been an important topic among DSOs, due to the flexibility that it provides to the grid. EDP Distribuição (EDPD), the main Portuguese DSO, has partnered up with a well-known manufacturer, SIEMENS, a research center, INESC I&D, and a local University, University of Évora, to install a Medium Voltage (MV) Storage facility that is able to work in both grid connected and islanding mode with the University secondary substation. To achieve this, the MV client University of Évora is connected to the grid in such a way as to enable both operating modes. The ESS, which contains lithium batteries modules, has a rated Power of 472kVA and a capacity of 360 kWh. The ESS was built to be modular and moveable so it can be installed in other nodes of the grid or upgraded with more power and capacity.The ESS automatically reconnects to the grid after the voltage returns to normal operation values ensuring an almost continuous operation. In this study, the authors will present the knowledge acquired in the last 2 years of experience operating a MV Storage unit in the Portuguese grid. During this time, the ESS system went into islanding mode for several times due to unplanned grid outages, which constitutes a good baseline for the ESS behaviour assessment regarding islanding. These real cases of successful and unsuccessful islanding operation will be the focus of this paper as well as an analysis on the motives for the few unsuccessful cases.