Precise Fault Location Detection for 400kV Overhead Transmission Lines and Underground Cables

Crozier, Jay David

4. term

Energy Engineering, Master

2026

2026-01-09

34

Danmark flytter i stigende grad transmissionsnettet under jorden, hvilket skaber hybridforbindelser med skiftevis luftledninger (OHL) og jordkabler (UGC). Denne opbygning gør det sværere at finde den præcise fejlplacering (fx ved kortslutninger), fordi traditionel, impedansbaseret beskyttelse bygger på en simpel, lineær sammenhæng mellem målt impedans og afstand, som ikke holder på tværs af blandede medier. Dette speciale vurderer en to-ende synkroniseret vandringsbølge (TW) algoritme som et alternativ på Energinets planlagte 400 kV Kassø-Landerupgård-forbindelse. Der blev opbygget en detaljeret elektromagnetisk transientmodel i PSCAD med frekvensafhængige fasemodeller for at gengive bølgeudbredelsen i krydskoblede XLPE-kabler (plastisolerede). Undersøgelsen tester hypotesen om, at en enkelt "systemeffektiv hastighed" - én antaget bølgehastighed - kan gøre fejlbetragningen lineær på tværs af både OHL og UGC. Algoritmen kunne identificere bølgefronters ankomst trods dæmpning i overgangen mellem luftledning og kabel. Men en enkelt kalibreret hastighed gav cirka 3 % lokaliseringsfejl for fejl langt fra enderne. Årsagen er, at den samlede udbredelsestid afhænger af de konkrete længder af luftledning og kabel, bølgen passerer, ikke af en fast gennemsnitshastighed. Konklusionen er, at meter-nøjagtighed kræver en segmenteret hastighedsprofil, der tilpasses den specifikke fejlsone, frem for en ensartet hastighedsantagelse.

As Denmark moves more of its high-voltage transmission grid underground, many routes will mix overhead line (OHL) spans with underground cable (UGC) sections. This hybrid design makes it harder to pinpoint the exact fault location (such as short circuits) because traditional impedance-based protection assumes a simple, linear link between measured impedance and distance, which no longer holds across mixed media. This thesis evaluates a two-terminal synchronized traveling-wave (TW) algorithm as an alternative on Energinet's planned 400 kV Kassø-Landerupgård connection. A detailed electromagnetic transient model was built in PSCAD, using frequency-dependent phase models to capture wave propagation in cross-bonded XLPE (plastic-insulated) cables. The study tests whether a single "system effective velocity" - one assumed wave speed - can make fault calculation behave linearly across both OHL and UGC. The algorithm detected wavefront arrivals even though signals were attenuated at the OHL-UGC interfaces. However, using one calibrated speed produced about a 3% location error for faults far from the terminals. The reason is that total travel time depends on the exact lengths of overhead line and cable the wave crosses, not on a constant average speed. Therefore, meter-level accuracy requires a segmented velocity profile that adapts to the specific fault zone instead of a uniform-velocity assumption.

[This summary has been rewritten with the help of AI based on the project's original abstract]

Fault Location ; Hybrid Transmission Lines ; Hybrid Transmission System ; Hybrid Power System ; Travelling Wave (TW) ; Power System Protection ; Electromagnetic Transients (EMT) ; PSCAD/EMTDC Simulation ; Two-Terminal Algorithm ; Sheath Cross-Bonding ; Underground Cables (UGC) ; 400 kV Transmission ; Impedance Mismatch

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