Listen to Your On-Load Tap Changer: It’s Trying To Tell You Something

March 10, 2022

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 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.

New Vibro-acoustic measurement (VAM) 

Complementary to this approach, the vibro-acoustic measurement (VAM) records the vibrations produced during the switching operation. The evaluation of the VAM results relies on the comparison with reference data such as a fingerprint or the comparison with sister units.

In order to obtain the acoustic signals, acceleration sensors are mounted on the OLTC cover or the transformer tank wall. The sensors are installed on magnetic mounting plates or screwed to the OTLC cover. This method offers the possibility to perform measurements on an energized transformer and, accordingly, provide valuable information on the condition of the OLTC without the need for outages. By recording a detailed vibration pattern and comparing it to a fingerprint, it becomes possible to detect and to track changes of the mechanical integrity of the OLTC.

Reduce diagnostic blind spots

If the transformer is disconnected from the grid, a simultaneous vibro-acoustic and dynamic resistance measurement can be performed. Combining the VAM and DRM methods gathers additional insights into the switching sequence. The VAM and DRM measurements on an OLTC represent mechanical and electrical time sequences, respectively, and provide an opportunity for a combined evaluation based on complementary data. By combining the two approaches, blind spots from the individual methods are compensated, and an in-depth assessment of the overall OLTC switching operation is achieved.

Discover VAM1 

Listen to our podcast

(Length: 16:12 minutes)

In this episode of Energy Talks, you will learn more about the vibro-acoustic measurement (VAM) with the help of our VAM experts - Dr. Karsten Viereck from Maschinenfabrik Reinhausen and Christoph Engelen.

Energy Talks features various episodes related to power system testing. You can find all episodes on our podcast landing page.

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