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    E-lesson

    OLTC Course – e-lesson #8 – Special cases of OLTC testing

    OLTC Course - e-lesson #8 - 850 x 400 illustration
    Course: Master’s level

    Hosted by: Raka Levi / Master's level

    Eighth lesson of the OLTC Course is the second lesson on the Master's level, as well as the final lesson of the entire course, in which Dr. Raka Levi discusses special OLTC constructions and particular test results expected for those.

    This lesson covers special and less common cases encountered in the testing of On-Load Tap Changers (OLTC). It addresses configurations such as series transformers, series auto transformers, and bias windings, which are used to reduce operational challenges like high currents during tap changer operation. The lesson also explores phenomena such as remnant magnetism, which can affect test results, and provides insights into testing errors and how to properly analyze test data. Additionally, it discusses innovative solutions like regulators, which separate the transformer from the tap changer to reduce failure rates.

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    Load tap changers have gone through various design changes over the time and application of test techniques to particular configurations, like regulators, are discussed. Special emphasis is given to remanent magnetism and demagnetization procedures.

    Keywords: dynamic test results, diagnostics, series transformer, booster winding, bias winding, demagnetization, remanent magnetism

     

    About the author

    Raka Levi

    Raka Levi

    Dr. Levi spent his entire career in diagnostic testing transformers and other substation apparatus, while the last 15 years dealing with tap changers. He is senior member IEEE and vice-chairman of the working group for revision of Guide for testing power transformers. Raka Levi consulted clients on all 5 continents in the field of condition assessment and substation monitoring.

    Edis Osmanbasic

    Hitachi Energy

    Edis Osmanbasic is a Senior Project Lead Engineer for BESS and Microgrids at Hitachi Energy Sweden. His responsibilities are all technical aspects of the full BESS station from selecting main components to defining full system automation. Before this role, he was an Application and Testing Specialist at DV Power, Sweden for 14 years. His experience involves diagnosing transformer test results and defining and proposing maintenance strategies for HV equipment. His focus was developing test methods for condition assessment of transformers, OLTCs, and generators. Edis has published numerous papers on DRM methodology and transformer testing methods. He holds an MS in electrical engineering.

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