People of Electromontaj: 400 kV OHL Cernavodă - Stâlpu

The latest Electromontaj project, of an impressive magnitude, in our first documentary film: “The people behind the 400 kV Cernavodă-Stâlpu overhead power line”.

It’s about the incredible people who made it happen with passion and emotion and effort.

400 kV OHL Cernavodă-Stâlpu is a project developed by Transelectrica TSO, co-financed by the Mechanism for Connecting Europe – Connecting Europe Facility and implemented by the Electromontaj group, as contractor.

The project is part of the North-South Interconnection East Electricity Corridor and aims to strengthen the cross-section between the west coast of the Black Sea and the rest of the European system , contributing at the same time to the strengthening of the electricity transmission network in Romania, to the increase of the interconnection capacity between Romania and Bulgaria and to the integration of the wind energy produced in the Dobrogea area.

The 400 kV double circuit (d.c.) Cernavodă – Stâlpu overhead power line and connection to the Gura Ialomiței station crosses the administrative territory of three counties: Constanța County (6 kilometers with double circuit), Ialomița County (94 kilometers with double circuit) and Buzău County (54 kilometers with double circuit) and passes through 22 administrative-territorial units: Cernavodă, Seimeni, Stelnica, Bordușani, Făcăeni, Vlădeni, Mihail Kogălniceanu, Gura Ialomiței, Șăndărei, Valea Ciorii, Scânteia, Grivița, Miloșești, Padina, Pogoanele, Smeeni, Gherăseni, Costești, Stâlpu, Saligny, Fetești and Luciu.

The 400 kV double circuit line starts on the northeastern front of the 400/110 kV Cernavodă power station and heads southwest following the two existing 400 kV lines, respectively the 400 kV Cernavodă – Pelicanu OHL and the 400 kV Cernavodă – Gura Ialomiței OHL.

The total length of the line route is 158.24 km and includes 509 400 kV high voltage towers.

The 400 kV d.c. OHL Cernavodă – Stâlpu is divided into two sections, namely:

• section I between Cernavodă station and Gura Ialomiței station with a total length of 55.1 km of double-circuit OHL (including the Danube and Borcea branch crossing panels)
• section II between Gura Ialomiței station and Stâlpu station, with a total length of 103.14 km, which includes the Cernavodă – Stâlpu and Gura Ialomiței – Stâlpu OHL 400kV circuits.

TECHNICAL DETAILS OF IMPLEMENTATION

In the area of ​​Seimenii Mici, according to the project developed by Electromontaj S.A., the Danube crossing was carried out on a panel of approximately 2.5 km divided into three sections: terminal – support – support – terminal.

The actual crossing of the Danube was carried out through an opening of approximately 1,132 m with 150 m high towers, the tallest in Romania to date and weighing approximately 320 tons each.

The erection of the 150m high towers was carried out in sections, with a 600-ton crane.

1,402 cubic meters of concrete and 133 tons of reinforcement were used to build the foundations of a single tower. The erection of a single such tower required a time interval of approximately 3 weeks.

Near the commune of Stelnica, the crossing of the Borcea branch was carried out, also according to the project developed by Electromontaj S.A., with a length of the crossing panels of 1.7 km, divided into three sections: terminal – support – support – terminal. The crossing of the Borcea branch was carried out with high-voltage towers, 100 m high.

For the construction of the 400 kV Cernavodă – Stâlpu OHL, including for crossing watercourses, “Danube” type towers were used, made of rolled steel profiles, joined by bolts and protected against corrosion from the factory by galvanizing and painting. The towers that make up the crossings of the Danube and the Borcea Branch have a total weight of 1,855.36 tons, being made of rolled angle profiles with dimensions from L40x5 for bracing to 2xL300x33 for uprights.

The heaviest weight is given by the STD-400CS+50 tower (height 150m) which reaches 318.78 tons, with a console attachment height of 132 m and a console span of 43 m.

The foundations of the supporting and terminal towers that ensure the crossing of the Danube, the Borcea branch and the Ialomița River were made on deep-drilled columns (approx. 30 – 40 m), embedded in the bedrock for good stability and flood resistance, taking into account the geological and hydrological conditions of the sites, as well as the type of towers and their operating conditions; the columns were embedded in a general concrete foundation.

For towers in areas with stable soils and a hydrostatic level below the foundation level, mushroom-type cast foundations were made, connected to each other with concrete belts.

For the foundations of the supporting towers that make up the Danube crossing, located in a flood zone, the solution of raising them above ground level by 5m was chosen.

The foundations of the crossing towers ensure the necessary stability and resistance with a total quantity of high-strength reinforced concrete (C30/37) of 3,922 m3 for the rafts and 4,271 m3 for the bored piles.

Acestor cantități corespund 311.500 kg si respectiv 394.926 kg de armătură BST500S. Piloții forați pe care se sprijină radierele masive au adâncimi de până la 33 m cu diametre de Ø 1.200 mm însumând un total de 4.104 ml de foraj.

The two crossings were made with a phase composed of 2 active conductors of AACSR 560/315 mm2 and were equipped with a protective conductor with embedded optical fiber, type OPGW 336 mm2, equipped with 36 G655NZDSF optical fibers and with classic ACS 336 mm2 protective conductors, type 336-A20SA.

The crossing of the Danube and the Borcea Branch was equipped with the following types of insulator chains: triple support chains, consisting of 3 branches, with a total breaking load of the chain of 900 kN, on the support pillars and quadruple tension chains consisting of 4 branches, with a total breaking load of 1200 kN, on the tension pillars towards the crossing.

The works for this project were carried out in a proportion of 90% with Romanian products. All the towers that are part of this project were produced by Electromontaj in its own production unit, at the Metal Pole Factory, and were tested in the Electromontaj Towers Testing Station in Bucharest, one of the largest in the world.

Rope-type conductors with a nominal section of 350/69 mmp, produced at IPROEB Bistrița, were used to equip the overhead line.

The successfully completed project falls into the type of works in the category of “transmission network development process” mentioned in the “Romania’s updated energy strategy for the period 2020-2027”.