Analysis Of The Methodology Adopted By The Italian Regulatory Authority For Identifying Major Event Days

The Italian regulatory mechanism for quality of service in electricity distribution links the tariff to the SAIDI indicator, net of contributions from exceptional events. In the year 2004 a two-step statistical methodology was introduced to identify major event days (MEDs). This statistical criterion defines a potential MED as a day with a daily CAIDI greater than the mean plus one standard deviation of the annual distribution of daily CAIDI for the relevant spatial unit, the territorial district; within this subset, a MED is a day with a daily SAIDI greater than the mean plus three standard deviations of the daily SAIDI distribution. A one year experience with this approach confirms its validity and suggests an alternative definition of the first step. The suggested definition is still based on a model-free statistical approach, but refers instead to percentiles. This modification would enhance the robustness of the method and enable to drop a currently necessary ex-post adjustment of the regulatory procedure