Phase Shifting Transformer On-Site Testing – Best Practice

Phase-Shifting Transformers (PSTs) are critical assets for power flow control, congestion management, and grid stability in modern transmission systems, with growing relevance also in distribution networks due to renewable integration. Their operational importance requires a condition-assessment approach that goes beyond factory acceptance testing and focuses on design-aware, on-site electrical diagnostics throughout the service life. This paper presents a structured methodology for field testing of PSTs, linking transformer topology, core configuration, and load tap changer (LTC) arrangement to feasible measurement methods, test sequences, and data interpretation.