500 450 400 350 300 250 200 150 100 50 41% Average SAlDl From MV Overhead Lines (OHL) = 45 Three Times Average SAlDl From MV OHL = 135 8% of Circuits Experiencing More Than Three Times the Average SAIDI From MV OHL 15% 10% 8% 5% 6% 4% 2% ≤ 15 ≤ 30 ≤ 45 ≤ 60 ≤ 75 SAIDI (min) figure 2. Percentage of events and SAIDI times. MV is medium voltage. OHL is overhead lines. interruptions within a year. Table 1 shows several U.S. states and utilities that have now adopted CEMI reporting in the public domain for grid regulation. To aid in reliability improvement efforts, Florida Power & Light and Gulf Power are using a new metric, CEMM, to measure and improve performance for the customers most affected by momentary interruptions. The adoption of CEMM has highlighted problem areas for grid modernization and automation, resulting in significantly increased reliability for customers during both normal conditions and major storms. The CELID metric established by IEEE Standard 13662012 captures another important aspect of performance. It reports on customers experiencing long interruption durations either in aggregate or from a single event. CELID allows the utility and regulators to see how performance differs for the worst-served feeders compared to the system average. Similarly, the Delaware Public Services Commission requires utilities to report on the total number of customers that have experienced a cumulative total of more than eight hours of outages. However, CELID is not yet a widespread regulatory reporting requirement in most jurisdictions. Reporting long-duration interSystemwide Feeder-Level MAIFI SAIDI and SAIFI Electricity Customer ruptions is also popular in other parts of the world, such as Britain and Scandinavia. British energy regulator Ofgem requires reporting on the number of unplanned and pre-arranged customer interApril 2022 Show Issue Momentary Interruptions Commentary: This is where it started in the 1970s. SAIFI and SAlDl have long been the nucleus. Duration of Outages Typical Outages 5 min to Several Hours Long Interruptions > 12 Hours Size of Circle = Relative Level of Utility Use of This Metric figure 3. Interpretation of key utility reliability metrics. ieee power & energy magazine 121 ruptions by duration bandings under both normal conditions and exceptional events. The Swedish Energy Markets Inspectorate and Finnish energy regulator Energiavirasto require reporting on the number of interruptions longer than 12 and 24 hours, respectively, as part of their arrangements for compensating long-duration outages. The approaches of these organizations could offer useful models for U.S. states to modernize their reliability reporting. Groups that are taking greater steps toward customer-oriented reporting and shifting toward new or lesser-used metrics are indicating a path forward for other energy systems to follow. Figure 4 shows our interpretation of how regulators and utilities are moving toward more customercentric measures. Major Event Days ≤ 90 2% ≤ 105 ≤ 120 ≤ 135 > 135 8% Level of Impact