This paper reports the results of the analyses on the accuracy of algorithms commonly adopted in instruments devoted to the detection and characterization of voltage dips (also called sags). This analysis is particularly interesting because the results of dip measurements are used for calculation of severity levels and site indexes that are important parameters in the assessment of quality level of power supply but also for selecting equipment with proper intrinsic immunity. Anyway, instruments fordip measurement still have unresolved technical and theoretical issues related to the characterization of their metrological performance, 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 because of the adoption of the detection algorithms adopted in agreement with standard. It starts with a discussion about parameters that characterize voltage dips. Then, the analytical calculations of systematic deviations in the event characterization, introduced by the most diffused dip detection algorithms, in simplified measurement situations, are presented, underlining their remarkable impact with particular attention to short-dip event. The obtained relations are experimentally verified on a commercial power quality instrument. Brief remarks about the analysis of the main algorithms, alternative to that of the standard, for voltage dip detection are also reported.