Accuracy Analysis of Voltage Dip Measurement

 This paper analyzes accuracy of algorithms commonly adopted in instrument devoted to the detection and the characterization of voltage dips (also called sags). This analysis is particularly interesting because the results of dip measurements are utilized for calculation of severity levels and the site index assessment that are parameters adopted in determination of quality level of power supply, but also in developing planning and design criteria of new electrical power grid or for selecting equipment with proper intrinsic immunity. Anyway there is a certain degree of freedom left to instrument manufacturers (f.i. the choice of dip detection algorithm) and it can be found that different instruments significantly disagree in some actual measurements. The paper starts with an insight about dip phenomenon analyzing how accuracy impacts on severity index calculation. The results are applied, for accounting the systematic deviations in testing accuracy of commercial instrument, is presented. Then, experimental results derived form the accuracy testing in dip measurements of a commercial power quality instrument are shown.