Identification and interpretation of the signal from the diverter switch in the vibro-acoustic measurements of the OLTC

The on-load tap changer (OLTC) is a critical functional part of a power transformer used in a wide range of power classes, from distribution transformers to high-power transformers. Its purpose is to regulate the voltage levels of a transformer and provide a stable output voltage while the input voltage or load conditions may vary. As the only moving part of the transformer, the OLTCs require maintenance. Currently, the vacuum OLTC is the most common type of OLTC, having fairly stable operation. This type of OLTCs require only very long maintenance intervals, up to 300,000 switching operations, which corresponds to more than the service life for certain applications. Rare or even missing maintenance can cause a high sense of uncertainty for operators, while reliable monitoring could provide more confidence. As a non-contact, non-invasive method, vibroacoustic measurement (VAM) is successfully used for monitoring of OLTCs operating at high voltage. The paper focuses on the most important part of the VAM method – the processing and interpretation of the measured signal. One of its features is the labelling of the signal that enables the interpretation and, in particular, the exact timing measurement for the OLTC and the associated diverter switch (DS). Since the DS is a spring-operated device, the time measurement is a reliable way to ensure its normal operation.