A Study of the Power Quality of a Rural Electric System

This presentation discusses the results of a three-year study of distribution system power quality as seen at the low-side bus of distribution substations. Data from 85 substations was used in this study. The purpose of the project was to characterize the system power quality and to determine what influences it. Many variables, both system related and weather related, were analyzed. Although there have been previous studies of power quality, this is the first to take a comprehensive look at environmental influences on power quality. One surprising conclusion is that temperature is a stronger predictor of the number of voltage sags than lightning flash occurrence. The system parameter study showed both agreement and disagreement with earlier studies. The results of analysis of the data is discussed in detail along with their implication to improving power quality on rural systems. Besides studying what influences the number of voltage sags, the correlation between the voltage sag index (SARFI) and interruption frequency index (SAIFI) was also investigated. A very strong correlation of an inverse relationship between the two was seen. This implies that by only concentrating on improving power quality one can increase the number of system interruptions. The discussion explores what further studies are needed to find means to improve one without degrading the other