Characterization of voltage dips and swells in a DG embedded distribution network during and subsequent to islanding process and grid re-connection

Stand-alone operation of distributed generations (DGs) under islanded mode is achieved by appropriate switching of controllers from grid-parallel to stand-alone mode. Conversely, during grid-restoration, reverse switching operation is employed. These operations cause voltage quality issues; among these issues, voltage dips and swells are two crucial events which are encountered during and subsequent to islanding. This paper characterizes the voltage dips and/or swells caused by the islanding of DG and its subsequent pre- and post-islanding events. Pre-islanding events encompass the fault initiated islanding scenarios, whereas post-islanding events are associated with transitional state, island stabilization and grid-reconnection states. Considering pre- and post-islanding scenarios, this paper classifies and characterizes the voltage dips and swells using an algorithm incorporating three-phase voltage ellipse and 3D polarization ellipse parameters. Three-phase voltage ellipse parameters, namely, major axis, minor axis and inclination angle of ellipse, are exploited for characterization and classification of voltage dips/swells based on their affected phases, whereas 3D polarization ellipse parameters are employed for classifying seven dip-types, namely A, B, D, F, E, C, and G. Islanding and its subsequent scenarios are simulated using a test distribution network of Australia embedded with DG, and the voltage dips and swells are characterized using the proposed algorithm.