۱- Introduction

۲- Impact Factor

۳- Methodology for determining the Impact Factor calculation parameters

۴- Application of the proposed methodology

۵- Conclusions

References

Abstract

This paper proposes a methodology for determining a site index that considers the equipment sensitivity to voltage sags, the variation in their level of sensitivity, and the influence of unbalanced sags on three-phase loads. Some single-event characteristics are easily applicable when obtaining site indexes, however, they are overly generic to consider all the above-mentioned aspects, and the more specific indices present the inconvenience of calculation parameters that are dependent on the equipment type, which makes them more adequate to quantify the impact of voltage sags on certain loads rather than to evaluate the sites’ performance. In this context, the proposed methodology aims to obtain a single set of calculation parameters that is applicable to all cases, allowing large-scale assessments. For this purpose, a statistical approach is adopted, considering the correlation between the index and the number of equipment trips, in order to define the adjustment most correlated with the sensitivity level of different types of loads. The Impact Factor is used as a basis in determining the desired index. A case study illustrates the application of the proposed methodology, showing how these aspects can be addressed from a better definition of the Impact Factor.

Introduction

With the modernization of industry and the electric sector deregulation, power quality (PQ) has become an increasingly relevant issue for both consumers and utilities [1,2]. Among PQ disturbances, voltage sags are one of the most critical problems. In certain industries, a sag event lasting only a few milliseconds can cause a prolonged interruption of processes, which may take several hours to be restarted, generating high financial losses due to downtime [3,4]. Nevertheless, despite the relevance of these phenomena, few countries in the world present criteria for their regulation [5]. In the case of Brazil, there have recently been great advances in this regard with the update of the Distribution Procedures (Prodist) Module 8 [6], and a new index called “Impact Factor” (IF) has been created. However, the way in which its calculation parameters were determined has not been clearly explained, raising several questions about their adequacy. The IEEE Std. 1564 [7], in turn, provides methods to quantify the events severity and the performance of sites and systems. The site indexes are calculated from the single-event characteristics, such as the voltage sag energy (Evs) or the voltage sag severity (Se), of all events measured in a given period of time, and the system indexes are calculated from the site indexes. Besides Evs and Se [7], a number of other single-event characteristics have also been proposed in the literature, such as the sag score [8], the lost energy (W) [9], the missing voltage time area (MVTA) [10], the sag SAIFI [11], the magnitude duration severity index (MDSI) [12], and the sag severity index (SSI) [13]. However, although there are several indices, there is still no consensus on which ones should be used.