Comprehensive severity evaluation of voltage sag based on entropy coefficient method considering subjectivity and objectivity

Abstract

A comprehensive severity evaluation index of voltage sag is proposed in this paper. Firstly, the grade classification of the evaluation index is identified according to the IEC 61000-2-8 table, and each duration interval is mapped to a normalized interval. Secondly, the influence degree of duration and magnitude are calculated respectively using subjective analytic hierarchy process (AHP) and objective weight function method. Then, by using entropy coefficient method with combination of AHP and weight function method, the influence degrees of duration and magnitude are obtained with consideration of subjectivity and objectivity. Finally, assuming that duration and magnitude are independent of each other, using the plural form and following the example of existing indices, several forms of voltage sag comprehensive influence degree index is proposed to evaluate voltage sag severity. Moreover, the evaluation results of the sag data coming from the power quality monitoring system of a city in China are obtained using the proposed method. By using entropy coefficient method, the results are more reasonable compared with one single method. Besides, the voltage sag severity of the sites can be described more accurately and truly through the comprehensive influence degree index based on the entropy weight method in actual power system.