Severity assessment issues for short voltage dips

This paper analyzes the impact of the systematic deviations that can be found in the measurements of voltage dips (also called sags) adopting algorithms in agreement with standards as it is commonly done by commercial instruments. This analysis is particularly interesting because the results of dip measurements are utilized for the calculation of severity levels and the assessment of site indexes that are parameters adopted in determination of the quality level of the power supply, but also to develop planning and design criteria for new electrical power grids or to select equipment with proper intrinsic immunity. The paper starts with an insight about dip phenomenon presenting the most important systematic deviations introduced by standard algorithms. Then, the remarkable effects on severity index calculations are presented with particular attention to short dip events. The conditions of non-detection, for dip shorter than 1 cycle, are analytically calculated and a great ambiguity for a dip even shorter than 2 cycles is shown.