EVALUATION METHOD OF VOLTAGE SAG SEVERITY FROM GRID SIDE BASED ON POINT-TO-LINE DISTANCE INDEX

Abstract

Evaluation of voltage sag severity from grid side according to the monitoring data is a very important task for utilities. This paper presents an approach to evaluate the system voltage sag severity based on point-to-line distance index. Representing the sag events in the duration-magnitude plane, the scatters are analysed to obtain the distribution characteristics of all sag events. Cluster analysis is applied to duration of all the sags to obtain serval intervals. Then the medians of retained voltage are solved by total events in different intervals to plot the median line. The severity index named point-to-line distance is defined for a region as the average of the distance from point below the median line to the median line. The method is applied to evaluate the voltage sag severity of 10 regions in an urban city. The feasibility and rationality of the method can be testified by the comparison of the evaluation results with other indices. The method is based on a large number of monitoring data and achieves the system evaluation directly considering both duration and magnitude.