Voltage Sags Indices and Statistics

Abstract

Voltage sag indices are a way of quantifying the performance of the power supply, as far as voltage sags are concerned. Indices can be defined for individual events, for individual sites, and for a whole system. A standard method for single-event methods is part of IEC standard 61000-4-30. This thesis emphasizes the importance of voltage sag indices and different methods for calculating three-phase voltage sag characteristics. Three-phase events measured in a medium network voltage over period of one month were analyzed, results examined and statistically evaluated. An algorithm for calculating voltage sag characteristics and indices was created in Matlab. Algorithm detects if the event is voltage sag, interruption or swell. Two different methods, symmetrical component method and six-phase rms method, for calculating sag type are used in the algorithm. Single-event characteristics as duration, retained voltage, voltage sag energy index, voltage sag severity and sag type are calculated for each event and summarized in synoptic table. After single-event characteristic results were satisfactory, site and system indices were implemented in MatLab and some statistics were carried out. Also various implementation issues with a detailed description of symmetrical component method and six-phase rms method were written.