Listen to your on-load tap changer; it’s trying to tell you something

New Vibro-acoustic measurement (VAM) Upgrade Option for TESTRANO 600

OMICRON now offers the VAM1 enabling users to perform a vibro-acoustic meas-urement on an on-load tap changer (OLTC).

The OLTC of a power transformer plays a vital role in maintaining a stable voltage level within the electrical grid. It’s a mechanical switching device that regulates the system voltage by adjusting the transformer turns ratio. Due to the thermal and me-chanical stresses generated when the load current is switched, various OLTC compo-nents such as the contacts can suffer wear and tear over their lifetime.

During the switching operation of the OLTC, a unique vibration pattern is present. The VAM1 records these vibrations using up to three acceleration sensors mounted to the transformer tank wall. Recording a detailed vibration pattern and comparing it to ref-erence data such as a fingerprint, makes it possible to detect and track changes in the OLTC’s mechanical integrity.

Apart from the raw signal of the acceleration sensors, a frequency-time diagram and an envelope curve are derived, facilitating the comparison. This post-processing step is an important tool that makes the measurement data better able to withstand exter-nal disturbances. In addition, a single-phase DRM curve and the motor current are recorded. The approach of combining vibration patterns and electrical measurements enables test engineers to perform an in-depth analysis of resistive and reactive OLTC types.

The VAM is a Primary Test Manager™ (PTM) only test. PTM supports you in the best possible way during diagnostic tests via wiring diagrams and asset-specific test plans in accordance with interna-tional standards. For a comprehensive analysis, PTM offers automatic result assessments and com-parisons, as well as customized reporting.