Precise Fault Location Detection for 400kV Overhead Transmission Lines and Underground Cables
Author
Term
4. term
Education
Publication year
2026
Submitted on
2026-01-09
Pages
34
Abstract
The transition of the Danish transmission grid towards underground cabling creates hybrid lines composed of alternating overhead line (OHL) and underground cable (UGC) segments. This topology complicates fault localisation by disrupting the linear impedance-distance relationship utilised by conventional impedance-based protection. This thesis evaluates a Two-Terminal Synchronised Travelling Wave (TW) algorithm as an alternative for accurate fault localisation on Energinet’s planned 400 kV Kassø-Landerupgård connection. A detailed electromagnetic transient model was developed in PSCAD utilising frequency-dependent phase models to replicate the complex wave propagation behaviour within cross-bonded XLPE cables. The investigation assesses the hypothesis that a single "System Effective Velocity" is sufficient to linearise the fault calculation across the heterogeneous medium. While the algorithm successfully identified wavefront arrivals despite attenuation at OHL-UGC interfaces, the results demonstrate that a single calibrated velocity yields a location error of approximately 3% for remote faults. This discrepancy arises because the total propagation time is strictly dependent on the specific lengths of OHL and cable traversed rather than a constant system average. Consequently, the study concludes that achieving metre-level accuracy requires a segmented velocity profile that adapts to the specific fault zone rather than relying on a uniform velocity assumption.
Keywords
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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