OMICRON Magazine

A power transformer’s on-load tap changer (OLTC) plays a vital role in maintaining a stable voltage level within the electrical grid. The OLTC is a mechanical switching device that regulates the system voltage by adjusting the transformer turns ratio. Due to the thermal and mechanical stresses generated when the load current is switched, various OLTC components such as the contacts can suffer wear and tear over their lifetime. In order to reliably assess the condition of the OLTC, increasingly advanced diagnostic tools have been developed. Typically, a static resistance measurement is performed to check for increased contact resistances. Moreover, a dynamic resistance measurement (DRM) records the change in current during the switching operation to analyze the OLTC’s timing and check for possible current interruptions. In addition to these electrical evaluations of the switching characteristics, mechanical analysis of the OLTC operation can be performed. The new TESTRANO 600 VAM1 accessory measures vibrations produced during the switching operation with acceleration sensors temporarily mounted on the transformer tank. The vibro-acoustic measurement (VAM) allows measurements to be performed on an energized transformer to provide valuable information about the OLTC’s condition without the need for outages. By recording a detailed vibration pattern and comparing it to reference data such as a fingerprint, it’s possible to detect and track changes in the mechanical integrity of the OLTC. Since the VAM can be performed without outages, it can be integrated into routine inspections, i. e., in-between scheduled maintenance intervals. Such regular tests will provide information about the current condition of the OLTC that prove invaluable for maintenance prioritization. TESTRANO 600 – WHAT’S NEW Listen to what your on-load tap changer has to say 20