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    E-lesson

    OLTC Course – e-lesson #5 – Testing resistor type on load tap changers

    Course: Intermediate level

    Hosted by: Raka Levi / Intermediate level

    In this lesson you will learn about:

    - Purpose of the test/reasons to perform diagnostics

    - Dynamic Resistance Measurement: history, testing, procedure

    - Good and bad examples of test results

     

    This lesson will focus on testing resistor-type on-load tap changers (OLTCs). We will explain the difference between dynamic and static tests, and introduce the concept of dynamic resistance measurement (DRM). DRM is a more advanced testing method compared to traditional static tests, as it can detect dynamic failures during fast OLTC operation. We will discuss the importance of parameters like transition time, ripple, and slope in DRM graphs, and how they can indicate issues in the OLTC. Additionally, we will cover vibration testing as a complementary method to DRM for detecting mechanical problems. The lesson will also touch on OLTC synchronization tests to ensure simultaneous voltage regulation across all phases. By the end, you will have a comprehensive understanding of the various testing techniques for resistor-type OLTCs and how to analyze the results.

    Keywords: dynamic test, diagnostics, resistor OLTC, transformer

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    About the author

    Raka Levi

    Dr. 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 Osmanbašić

    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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