Accuracy Analysis of Algorithms Adopted in Voltage Dip Measurements

This paper analyzes the accuracy of algorithms commonly adopted in instruments devoted to the detection and characterization of voltage dips (which are also called sags). This analysis is particularly interesting, because the results of dip measurements are utilized for calculation of severity levels and site indexes, which are important parameters not only in the assessment of the quality level of power supply but also in the selection of equipment with proper intrinsic immunity. Instruments for dip measurement still have unresolved technical and theoretical issues related to the characterization of their metrological performances, so it can be found that different instruments are significantly in disagreement in some actual measurements. This paper moves a step into the direction of deepening the knowledge about the measurement of voltage dips, pointing out the limits incident to the adoption of the detection algorithms indicated in the standards. It starts with a discussion about parameters that characterize voltage dips, in agreement with the standard. Then, analytical calculations of some systematic deviations in the event characterization, which are introduced by the most diffused dip detection algorithms, in simplified measurement situations, are presented, underlining their remarkable impact. The obtained relations are experimentally verified on a commercial power quality instrument, forecasting its systematic deviations.