Characterization of Voltage Dips and Swells in a DG-Embedded Distribution Network During and Subsequent to Islanding Process and Grid Reconnection

Stand-alone operation of distributed generations (DGs) under an 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 that 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 postislanding 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 three-dimensional (3-D) polarization ellipse parameters. Three-phase voltage ellipse parameters, namely, major axis, minor axis, and inclination angle of an ellipse, are exploited for characterization and classification of voltage dips/swells based on their affected phases, whereas 3-D 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.