Institutional Repository
Technical University of Crete
Technical University of Crete
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| URI: | http://purl.tuc.gr/dl/dias/B4CCAB59-2378-4898-A1A8-9DA20E454948 | ||
| Year | 2025 | ||
| Type of Item | Diploma Work | ||
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| Bibliographic Citation | Athina-Konstantina Antoniou, "Study of dielectric strength of medium voltage cables", Diploma Work, School of Electrical and Computer Engineering, Technical University of Crete, Chania, Greece, 2025 https://doi.org/10.26233/heallink.tuc.104049 | ||
| Appears in Collections |
Cables in medium voltage networks are exposed to two distinct electrical challenges: the continuous stress of normal operation and the abrupt, high-energy surges produced by lightning or switching events. Although the core insulation provides the primary dielectric barrier, the outer jacket frequently proves to be the first point of weakness during such fast transients. This study investigates the jacket’s response to 1,2/50 μs lightning impulses and demonstrates how materialformulation, surface condition, and construction details govern breakdown behavior.Impulse testing was conducted on five types of cable with different nominal voltages, varying jacket compounds (PVC, HDPE, MDPE, PPS+HDPE) and geometry, using a single stage impulse voltage generator. Samples were immersed in insulating oil and subjected to gradually increasing impulses. Oscilloscope traces, paired with visual inspection, confirmed breakdown events.Waveform compliance with IEC 60060-1 was verified via measurements and the generator was also simulated using ATP-EMTP.Breakdown voltages were evaluated through GEV analysis, yielding U10, U50, and U90 levels for each cable. Normalized breakdown field strength (kV/mm) was calculated by dividing breakdown voltage by the measured jacket thickness, offering a geometry-independent performance metric. Additionally, breakdown timing was analyzed to understand how and when insulation failure occurs within the impulse window, giving an indication of the tests and samples consistency.The findings offer clearly defined dielectric performance benchmarks for commonly used MV cable jackets and present a reproducible laboratory procedure encompassing sample preparation, waveform validation, and statistical breakdown evaluation. By quantifying impulse withstand limits and clarifying failure patterns under transient conditions, this work contributes to more robust oversheath assessment and supports the development of testing frameworks that betterreflect real-world electrical stresses.
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