This annex provides selected additional information to support the material in the main text of Chapter 9. The first section provides information on reliability measures. Next is a more detailed description of the characteristics of a modern grid than could be discussed in the section “A Modern Electric T&D System” of the chapter, followed by a more detailed description of some of the technologies discussed in the section “Key Technologies for a Modern Electric T&D System.” Finally, the cost analysis in the section “Costs of Modernization” in the main text is elaborated upon.

Reliability Measures in the Distribution System

The reliability of the distribution system is often measured using three indexes: the Customer Average Interruption Duration Index (CAIDI); the System Average Interruption Frequency Index (SAIFI); and the System Average Interruption Duration Index (SAIDI). CAIDI tracks the average duration (typically expressed in minutes) of customer interruptions over a given time period. SAIFI tracks the average number of customer interruptions in power service in a given period of time. SAIDI tracks the average number of customer interruptions in power service in a given time period. However, unlike CAIDI, the SAIDI average is calculated across the total number of customers served, rather than the number of customer interruptions. Results of applying these indexes are shown in Figures 9.A.1, 9.A.2, and 9.A.3 for the state of Ohio, which is roughly representative of the nation as a whole.

Characteristics of a Modern Electric Grid

The modern grid must meet the ever expanding needs of society and at the same time be reliable, secure, economic, efficient, environmentally friendly, and safe. In order to realize all these elements of modernity, our nation’s T&D system should achieve the following goals:

  • Emergency response. A modern grid provides advanced analysis for predicting problems before they occur and assessing problems as they develop. This capability allows actions that respond more effectively and minimize disruptions.

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