An Examination of Temporal Trends in Electricity Reliability Based on Reports from U.S. Electric Utilities

Publication Type


Date Published




Since the 1960s, the U.S. electric power system has experienced a major blackout about once every 10 years. Each has been a vivid reminder of the importance society places on the continuous availability of electricity and has led to calls for changes to enhance reliability. At the root of these calls are judgments about what reliability is worth and how much should be paid to ensure it.

In principle, comprehensive information on the actual reliability of the electric power system and on how proposed changes would affect reliability ought to help inform these judgments. Yet, comprehensive, national-scale information on the reliability of the U.S. electric power system is lacking.

This report helps to address this information gap by assessing trends in U.S. electricity reliability based on information reported by electric utilities on power interruptions experienced by their customers. Our research augments prior investigations, which focused only on power interruptions originating in the bulk power system, by considering interruptions originating both from the bulk power system and from within local distribution systems. Our research also accounts for differences among utility reliability reporting practices by employing statistical techniques that remove the influence of these differences on the trends that we identify.

The research analyzes up to 10 years of electricity reliability information collected from 155 U.S. electric utilities, which together account for roughly 50% of total U.S. electricity sales. The questions analyzed include:

  1. Are there trends in reported electricity reliability over time?
  2. How are trends in reported electricity reliability affected by the installation or upgrade of an automated outage management system?
  3. How are trends in reported electricity reliability affected by the use of IEEE Standard 1366-2003?

Year of Publication



Research Areas

Related Files