Sainz-Aja, Jose AdolfoPombo, JoãoBrant, JordanAntunes, PedroRebelo, José M.Santos, JoséFerreño, Diego2026-01-082026-01-082025-10-28Sainz-Aja, J. A., Pombo, J., Brant, J., Antunes, P., Rebelo, J. M., Santos, J., & Ferreño, D. (2025). Real-time rail electrification systems monitoring: a review of technologies. Sensors, 25(21), 6625. https://doi.org/10.3390/s25216625http://hdl.handle.net/10400.21/22459This research was funded by the RSSB (Rail Safety and Standards Board) via the project RSSB/COF-UOH-58. The technical support of RSSB to this work is greatly appreciated. The authors also acknowledge the support from FCT, through IDMEC, under LAETA, project UIDB/50022/2020.Most electrified railway networks are powered through a pantograph–overhead contact line (OCL) interface to ensure safe and reliable operation. The OCL is one of the most vulnerable components of the train traction power system as it is subjected to multiple impacts from the pantographs and to unpredictable environmental conditions. Wear, mounting imperfections, contact incidents, weather conditions, and inadequate maintenance lead to increased degradation of the pantograph–OCL current collection performance, causing degradation on contacting elements and assets failure. Incidents involving the pantograph–OCL system are significant sources of traffic disruption and train delays, e.g., Network Rail statistics show that, on average, delays due to OCL failures are 2500 h per year. In recent years, maintenance strategies have evolved significantly with improvements in technology and the increased interest in using real-time and historical data in decision support. This has led to an expansion in sensing systems for structures, vehicles, and machinery. The railway industry is currently investing in condition monitoring (CM) technologies in order to achieve lower failure rates and increase the availability, reliability, and safety of the railway service. This work presents a comprehensive review of the current CM systems for the pantograph–OCL, including their advantages and disadvantages, and outlines future trends in this area.engPantograph-overhead contact line interfaceCondition monitoringRailway maintenance strategiesDecision supportService safety and reliabilityRSSB/COF-UOH-58UIDB/50022/2020journal article10.3390/s252166251424-8220