Multi-Level Analysis of GNSS Observation Quality in Outdoor Substations for Deformation Monitoring

In outdoor substations, issues such as settling, step-ping voids, switch terminal box tilting, and gantry tower tilting are present. The traditional periodic manual inspection methods currently used for monitoring equipment and facility settling in outdoor substations cannot meet the needs of continuous monitoring. Due to its accuracy and timeliness, the Global Navigation Satellite System (GNSS) has become an essential means for displacement monitoring. However, using GNSS for monitoring equipment and facility settling in outdoor substations may encounter issues such as electromagnetic interference and signal obstructions. A thorough analysis and understanding of these factors on GNSS observation is essential and fundamental for further application. To address this issue, we propose a multilevel analysis approach of GNSS observation quality in outdoor substations aiming to provide insight into the quality of GNSS observations in substations. Specifically, we analyze the quality of observations at different levels by designing different quality indicators. Furthermore, we analyze the quality of GNSS observations at different levels, starting from the region, the receiver, the satellite system, and the signal, respectively. Finally, two substations were analyzed and the results showed that data quality in substations is significantly affected and reduced. The data integrity of almost all stations in the substation is less than 0.9, while the multipath index of all stations is greater than 0.5. Observation quality does not vary much between voltage levels, likely due to multipath and electromagnetic interference affecting GNSS. Comparing different receiver brands shows differences in data quality. Beidou and Galileo have slightly better data integrity than other satellite systems. New satellite signals offer higher signal-to-noise ratios and lower MP values.