Online condition monitoring of on-load tap changer in power transformers based on an electrical analysis

Online condition monitoring on the on-load tap changer (OLTC) is crucial for ensuring the reliability and performance of power transformers. OLTCs play an important role by regulating voltage levels and maintaining stable power supply. Failures can cause major operational disruptions and financial losses, thus making predictive maintenance vital. Traditional maintenance techniques rely on schedule inspections or reactive repairs and fail to detect future problems before they escalate. The proposed online condition monitoring technique focuses on analysing the currents and voltages from the high-voltage and low-voltage sides of the transformer, during the transient. Digital command signals from the OLTC controller trigger an acquisition routine that acquires approximately 7 seconds of high-resolution data at 25 k samples/s in order to capture the full transient event. Using a dedicated algorithm based on the electrical model of the power transformer, characteristic curves of the transient pattern are obtained, providing valuable insights into the OLTC condition. Case studies demonstrate this approach’s effectiveness, since this technique is non-invasive and straightforward. Overall, this method enhances operational reliability by enabling real-time and continuous monitoring, thus helping to identify issues in an early stage and supporting maintenance strategies.