As one of Sweden’s largest distribution companies, with close to one million customers, developing the electrical grid and working towards the highest possible supply reliability of power is of great importance to Ellevio. The company has prioritized to invest significant amounts in the replacement of older electrical facilities, capacity expansion etc. These development measures are expected to result in a more sustainable power system network. However, the goal of achieving the highest possible power supply reliability is still challenged by the fact that it is often difficult to determine the underlying causes for outages or when and where they are expected to happen, which in turn complicates the optimization process. This report aims at conducting a study on the variation in the start time of unplanned outages. The study is divided into different sections. A comparison between the power outage statistics of Ellevio and the total of Sweden is done in order to identify common and deviant trends. This is followed by a data analysis to study the most common underlying reasons for unplanned outages as well as determine the connections between observed outage trends and other factors, internal and external. An in depth analysis is also done of the outage trends in two of Ellevio’s operation areas, different in both geographical location and network design: Stockholm and Hälsingland. In this report it is also studied whether there is a connection between unplanned outages and electricity prices. Finally a statistical calculation is performed of the expected risk of an outage occurring depending on some factors. This is done to confirm some of the conclusions made in the report.   The results and conclusions of this report are aimed at providing knowledge about the circumstances surrounding the occurrence of Ellevio’s unplanned outages and suggestions on how to reduce the amount of outages and/or the time of repair.