Detecting power quality trends and thresholds: an annual analysis using the Mann-Kendall method

This study presents a trend analysis of power quality in the low-voltage power grid of Zurich, utilising data from 62 Janitza UMG 605 and UMG 511 power quality measurement devices installed primarily at connection points and transformer stations, in compliance with EN 50160 standards. The analysis focuses on power quality parameters such as harmonics (3rdto 25thorder), THDU, flicker and voltage unbalance, to identify trends over the past years. Data processing involved aggregating billions of measurements into monthly 95thpercentile per measurement device, phase, and category, followed by seasonal decomposition to isolate trends. The Mann-Kendall test is used to determine statistically significant trends. The analysis revealed that over half of the measurement devices showed increasing trends in the 3rdand 5thand harmonics, as well as in THDU and voltage unbalance. In contrast, flicker the 15th, 21stand 25thharmonics displayed negative trends. These findings underscore the importance of continuous monitoring and trend analysis in detecting emerging power quality issues and facilitating proactive interventions to ensure compliance with the threshold values specified in the EN 50160.