The effect of advanced load shedding in the formation of islanded MV grids

The increasing penetration of Distributed Generation (DG) units connected to the distribution network, driven mainly by environmental reasons, gives the opportunity to consider islanded operation of electricity distribution grids. Grid disturbances at the transmission level can lead to power interruptions in extended areas. This paper examines the possibility to operate an area with a significant penetration level of Combined Heat and Power plants (CHP) connected to a Medium Voltage (MV) grid autonomously. In this way, a loss of the connection with the High Voltage (HV) grid due to planned or unplanned events could be survived instead of resulting in an outage. Previous work has shown that local power balance is an important factor affecting the successful formation of an MV island; therefore in this paper an overall approach, concerning also large imbalances is presented. For this purpose, the operation of DG units, how these units manage to contribute to the voltage and frequency control during the switch to autonomous operation, how advanced load techniques can help, and how this affects the operational parameters (voltage and frequency) of the network are investigated.