Distribution system power quality assessment phase II: voltage sag and interruption analysis

The quality of electricity service required by customers of all classes is increasing. This requirement for increasing quality is due to many factors, including increasing sensitivity of the devices used by customers and their awareness of the impacts of small variations in the quality of the electricity supply. In the early 1990s, EPRI initiated a project called the distribution power quality (DPQ) project, which resulted in power quality monitoring at 277 distribution sites statistically chosen throughout the United States to gain valuable knowledge regarding the frequency and severity of power quality events. This paper presents the findings of a follow-on project, referred to as DPQ II, which was conducted in 2001 and 2002. This project resulted in characterizing power quality in terms of short-duration variations such as voltage sags, voltage swells, and voltage interruptions. The characterization was based on analysis of data from 480 power quality monitors at different locations in a power system spanning a date range from August 30, 1993, through December 12, 2002. The results of the analysis that are presented in this paper provide a unique opportunity to understand the electrical environment in terms of short-duration variations and further validate the findings of DPQI.