High tensile steel wire cores for High Temperature Low Sag conductors: A case study for Elia Belgium

– such as ACSS, GAP, and T-ACSR – have been widely deployed across Europe and North

America. Despite this, recent industry narratives have increasingly positioned composite core technologies as the sole solution for HTLS applications. However, both steel and composite core technologies offer distinct advantages and limitations.

This paper presents a case study conducted in collaboration with the Belgian transmission system operator, demonstrating that conductors with high tensile steel wire cores can fully meet the technical and operational requirements for upgrading conventional lines (e.g., ACSR and

AAAC) with High Temperature Low Sag conductors, while achieving the desired increase in transmission capacity.

A Belgian manufacturer of steel wire and steel wire products, introduced advanced steel wire grades – up to 2200 N/mm² – specifically for overhead power line applications. These highstrength wires maintain critical mechanical properties and exhibit consistent performance under cyclic loading, making them ideal for demanding environments. These high tensile steel wires are standardized under IEC 63248-2022, Annex A (grades S7A and S8A).

While galvanized steel wires have long been used for their corrosion resistance, their limited thermal stability restricts their use in HTLS applications. To address this, zinc-aluminium alloyed coatings such as the Zn95Al5 coating have been introduced more recently. These coatings offer up to three times the corrosion resistance of standard zinc and maintain thermal stability at temperatures up to 300 °C.

The Belgian transmission system operator , an early adopter of composite core technologies, provided a real-world case involving the upgrade of a homogeneous AAAC conductor

(operated at 75 °C, 1383 A). The objectives were:

• Increase ampacity by enabling operation at 150 °C continuous and 175 °C transient up to 2280A.

1 • Maintain or reduce conductor diameter. • Respect existing line constraints (sag and horizontal forces) in a wide range of temperatures. A Belgian engineering company specializing in overhead lines for transport networks, has modeled an ACSS conductor with a high-strength S8A steel core using overhead line design software. One could demonstrate that the ACSS/5MS8A conductor meets all the performance criteria – provided that in grid’s circumstances - the conductor is pre-stressed during installation.