Reaffirmed 2008. This standard is intended to aid the electric power industry in reporting and analyzing outage occurrences of transmission facilities. Use of systematic, precise definitions, which is essential for meaningful exchange of data, is promoted. The outage definitions and indices are intended for use in system planning models, operations and maintenance planning, and system design. The definitions and indices may not be sufficiently detailed to cover the information required for equipment design.

This standard defines terminology and indices for reporting and analyzing outage occurrences of transmission facilities. Outage definitions and indices are given for two general types of facilities-units and components. Units are functional facilities which transfer power between designated points, while components are specific pieces of equipment. Outage definitions are given both for describing the outage history of a particular facility and for describing groups of individual outage occurrences which are related in some way.