End To End Implementation of a 400kV 1x2500 mm2 XLPE Cable System With DTS Monitoring

XLPE cables with smooth Al sheath in HDPE, oil-filled conventional GIS terminations at

Ataşehir GIS, oil-filled composite insulator outdoor terminations at Ümraniye and Paşaköy, and premoulded insulated joints.

Key challenges during field execution included route revisions due to urban infrastructure and traffic constraints, staggered municipal permit approvals across seven jurisdictions, and adapting crossing methods to site-specific conditions. Route modifications were controlled based on maximum pulling tension and 5000 N/m sidewall pressure limits, and successive small-angle bends were resolved through a second revision. HDD lengths were optimized based on field trials and geotechnical surveys: 910 m → 192 m for Ümraniye–Ataşehir, and 600 m → 98 m for

Ataşehir–Paşaköy, reverting to trenching with conduit where necessary.

A cross-bonded system was applied, with a single-point bonded link box in Section 12 for future

GIS expansion. Thermal design was based on a continuous current of 1700 A, maintaining conductor temperature below 90°C, considering worst-case trefoil HDD at 4 m depth. The DTS system was planned as single-ended, with the interrogator at Ataşehir GIS, targeting 1 m spatial resolution and 1-minute measurement interval. Final commissioning includes a 330 kV, 1-hour AC resonance test, TEİAŞ provisional acceptance, and DTS-based thermal and current monitoring for RTTR evaluation.

This paper summarizes practical lessons in managing urban constraints, pulling limits, crossing method revisions, bonding integration, and DTS-based validation in complex urban underground cable projects.