For many years, electricity distribution companies have used sustained interruption indices as indicators of the reliability of service provided on their systems, Today, however, many electricity consumers are adversely affected by more subtle voltage disturbances such as sags and swells, Many utilities are ,yell aware of such service quality concerns and are implementing extensive monitoring systems to detect such disturbances and assess service quality in this regard, This paper presents a subset of work completed which pro,ides utilities with tools to make more complete service quality assessments, Indices del eloped to reflect system service quality with respect to all rms variations are presented, Example values for the indices are calculated using data from a national distribution power quality data collection project, Finally, an example application of the indices currently being made by a distribution utility is discussed.
