Condition Assessment of Power Transformer on-Load Tap-Changers Using Wavelet Analysis and Self-Organizing Map: Field Evaluation

An on-load tap-changer (OLTC) is the most maintenance-intensive subassembly on a power transformer. Vibration monitoring is an effective technique that can be used to assess the condition of an OLTC effectively and nonintrusively. The authors have developed a condition monitoring system for common types of OLTCs that enables the condition of tap changer contacts and associated drive system to be inferred from vibration signals. A number of prototype systems have been installed onto OLTCs in distribution zone substations for field trials. Particular emphasis has been given to the detection of faults in a particular type of older tap-changer that had been prone to a range of faults associated with the switching contacts and drive mechanism. For this type of tap-changer, it is possible to determine not only that the tap-changer is aging but also to identify the particular part that is degrading.