A procedure to analyze the impact of three-phase unbalanced conditions on switching overvoltages in systems with Distributed Generation

Given the relatively new context in which Distributed Geeneration (DG) is inserted in distribution systems, for certain aspects of the operation of this type of system there are relatively few studies of power quality considering the presence of DG. One of these aspects is certainly the possibility of DG operating under unbalanced three-phase operating conditions, which is quite common in distribution systems. The present work is intended to fill this gap with respect to issues related to switching overvoltages, particularly those originated from energizing the distribution lines. In particular, this work is devoted to analyze how the imbalance among the phases of a distribution system can impact the mentioned overvoltages in distribution systems with the presence of DG. A systematic procedure is developed to find out the worst case overvoltage scenario taking all the previous features into account. This procedure is tested in a real model of a distribution system and it was found out that the imbalance can be a factor impacting the magnitude of the largest overvoltage amplitude. The procedure developed in this paper can help improving relay and breaker settings for systems that might operate in the previously mentioned conditions.