ICCO Completes the Rural Damascus–Daraa 400 kV Transmission Line

International Consolidated Contractors Offshore SAL built the Rural Damascus–Daraa 400 kV double-circuit overhead transmission line for Syria’s Public Establishment for Transmission and Distribution of Electricity, under a supply and execution contract referred in July 2018. The line runs approximately 107 kilometres across 321 tower positions in the Rif Damascus and Daraa governorates, reaching mechanical completion in January 2021 and final handover on 18 February 2021.

The Rural Damascus–Daraa transmission project was built from the ground up.

Before the steel towers could rise across the route, each of the 321 proposed positions had to be surveyed, investigated and prepared for construction. Access had to be created. Excavations had to be completed. Foundations had to be designed around the loads imposed by different tower types and the conditions found at each location.

Only after that work could the structures, conductors and communication systems begin to form one continuous 400 kV transmission corridor.

A transmission route made up of 321 sites

A 107-kilometre transmission line may appear as a single project on a map, but it is constructed as hundreds of separate work locations. Each tower position had to fit within the wider electrical design while responding to its own local conditions.

The route had to account for:

• changes in direction

• ground conditions

• road and service crossings

• access for machinery and materials

• electrical clearances

• conductor span lengths

• tower loading and foundation requirements

The alignment included 321 tower positions across approximately 107 kilometres. That produces an average span of about 334 metres, although the actual distance between structures varied according to terrain, direction changes, crossings and engineering requirements.

Route planning shaped nearly every part of the project that followed. It determined where heavier structures were needed, how construction teams would move along the corridor and which sections could progress into tower erection and conductor installation.

Ground investigation before foundation work

A transmission foundation cannot be designed properly without understanding the ground beneath it. The project included ground investigations across the proposed tower positions, together with topographical surveying along the full route.

This was necessary because a long transmission corridor does not pass through one uniform type of ground. Excavation conditions may change from one position to the next. Some locations may require deeper or heavier foundations. Others may need additional treatment to achieve the required structural or electrical performance.

The civil scope included substantial quantities of ordinary excavation and rock excavation, together with concrete, reinforcement steel, tower-base construction, backfilling and compaction. These activities represented far more than site preparation: they established the structural base on which the entire line depended.

The work below ground

Much of the construction effort is now hidden beneath the completed towers.

At each position, reinforcement had to be installed and tower-base components aligned accurately before concrete placement.

That accuracy was essential. A small error at foundation level becomes more difficult to correct once the lattice structure is assembled above it. The foundation must also resist the weight of the tower, the pull of the conductors and the forces created by wind and operating conditions.

By the time the towers became visible, some of the project’s most important work had already been completed.

Four tower types across southern Syria

The 321 towers were selected according to their positions and functions along the route.

Suspension towers formed most of the line, carrying conductors through relatively straight sections. Corner towers were used where the alignment changed direction; these structures had to resist greater transverse forces created by conductors pulling from different angles.

Heavy-tension towers provided additional restraint at positions carrying higher mechanical loads. Terminal towers anchored the conductor system at the line ends, where the full tension of the circuits had to be contained.

The distribution of tower types allowed the route to follow its approved alignment while maintaining the structural stability and electrical clearances required for a 400 kV system.

Access as part of construction

No tower position can progress without a route for people, materials and equipment to reach it. The project included approximately 42 kilometres of temporary and permanent access-road work.

Working platforms were also established around tower positions to provide space for excavation, reinforcement, concrete placement, steel assembly and lifting operations. Drainage works were included at selected locations, while areas used during construction were prepared for rehabilitation after the main work was completed.

These activities are less visible than towers and conductors, but they can control the programme. An inaccessible tower position cannot move into excavation. A delayed foundation prevents tower erection. One incomplete structure can interrupt conductor stringing across several adjoining spans.

On a 107-kilometre route, access is not simply a logistical convenience. It is part of the construction strategy.

Building the conductor system

Once sufficient sections of the tower corridor had been completed and inspected, conductor installation could begin.

The line uses two 400 kV circuits, each made up of three electrical phases. Each phase was carried by a bundle of four sub-conductors, producing 24 conductor paths across the route. The project included approximately 2,568 kilometres of phase conductor.

Installing that quantity required controlled pulling and tensioning across successive tower spans. The conductors had to achieve their required sag while maintaining safe clearances from roads, services, the ground and other infrastructure.

The conductor system also included:

• 1,380 suspension-insulator strings

• 546 tension and corner-insulator strings

• 8,200 bundle spacers

• 5,400 vibration dampers

• 642 corona-ring and arcing-horn assemblies

Bundle spacers maintain separation between the four sub-conductors within each phase. Vibration dampers reduce repeated wind-driven movement that could weaken conductor strands or fittings over time. Insulator assemblies carry the conductors while separating the live system from the steel towers.

These smaller components are easy to overlook, but the long-term reliability of the line depends on them.

Earthing at every tower position

Every one of the 321 structures required a reliable connection to earth. Tower earthing provides a controlled path for lightning and fault currents to enter the ground; if the resistance is too high, electrical stress can build across the structure and insulation system.

The project included standard earthing systems and resistance testing at all tower positions. Eighty-four towers required additional counterpoise conductors and enhanced earthing arrangements.

That indicates the standard design was not sufficient at every location along the route. The need for additional treatment could only be confirmed by testing the conditions found at the individual tower positions, which made earthing another area where route-wide assumptions had to give way to location-specific engineering.

Fibre-optic communications along the line

The Rural Damascus–Daraa transmission corridor carries more than electrical power. Above the phase conductors run approximately 107 kilometres of conventional earthwire and a similar length of Optical Ground Wire, or OPGW.

OPGW performs two functions. Its outer structure helps shield the line from direct lightning strikes, while fibre-optic strands within the cable carry protection, control and communication data between different parts of the network.

The system included fibre joint boxes, splicing, terminations and optical testing along the route. These communication links allow protection systems to exchange information quickly and enable the line to be monitored as part of the wider electricity network.

A modern transmission asset must therefore combine structural, electrical and digital infrastructure within one operating system.

What ICCO delivered

International Consolidated Contractors Offshore SAL was responsible for the design, supply and execution of the line. Its scope included:

• route and topographical engineering

• ground investigation

• access-road and platform construction

• excavation and reinforced-concrete foundations

• tower supply and erection

• conductor and insulator installation

• earthing and lightning protection

• OPGW and fibre-optic communications

• testing and grid connection

Survey and geotechnical teams established the tower positions and ground conditions. Civil crews prepared access and foundations. Structural teams erected the towers. Electrical specialists installed the conductors, insulators and earthing systems. Telecommunications engineers completed the fibre links. Quality, safety and commissioning teams verified the completed installation.

Each team delivered a different part of the project, but the line could only enter service when those parts operated together.

Testing the completed 400 kV system

The final stage extended beyond checking whether every tower was standing. The full route had to be inspected and tested as one system.

Concrete and material testing formed part of the quality process during construction. Tower alignment and structural installation had to be verified. Conductors, insulators and earthing systems required electrical checks. The OPGW and fibre-optic links also had to be tested to confirm that protection and communication data could move correctly along the route.

Mechanical completion was reached on 26 January 2021. Final handover followed on 18 February 2021 after testing, grid connection and the completion of the project’s operating systems.

That process transformed 321 individual construction locations into one functioning high-voltage transmission corridor across southern Syria.

What the Rural Damascus–Daraa project demonstrates

The principal figures describe the project’s scale: approximately 107 kilometres of route, 321 tower positions, two 400 kV circuits, more than 2,500 kilometres of phase conductor, approximately 107 kilometres of OPGW, extensive excavation, reinforced concrete and access works, and enhanced earthing at 84 tower positions.

The figures also show why transmission construction cannot be understood from route length and tower count alone. Ground conditions affect excavation, foundations and earthing. Access determines whether construction can reach the individual sites. Tower type influences structural loading. Conductor installation depends on a continuous sequence of completed structures. Communications and protection systems must operate alongside the electrical line before the asset can enter service.

The completed towers are the most visible result of the project. The work beneath and between them is what made the line possible.