High-voltage link is completed

Nexans has completed a Eur 16.5 million project to create a new 33km underground 150kV link between the Coxyde and Slijkens substations on the Belgian coast.

Nexans has completed a Eur 16.5 million project for Elia, Belgium's transmissions system operator, to create a new 33km underground 150kV link between the Coxyde and Slijkens substations on the Belgian coast.

One of the major project challenges was in laying the cables under the Bruges-Ostend-Ghent canal, this was achieved by using an existing access tunnel owned by Aquafin, the water-treatment and sewerage utility.

The new high-voltage link forms an integral part of Elia's large-scale extension of the power network in the coastal region.

As well as reinforcing the network to respond to increasing demand for electricity it will also facilitate the grid connection of the Thornton Bank offshore windfarm.

For the underground link between Coxyde and Slijkens, three 150kV cables manufactured by Nexans' Charleroi factory were buried at a depth of 1.25m over a distance of 33km.

One of the three cables was equipped with integrated fibre optic technology in order to monitor temperature and power usage when the link is operating.

A drainage cable was also laid to drain circulating currents to the nearest earthed bonding point, this provides a measure of protection against short circuits for example, as well as preventing electrochemical corrosion of local structures such as steel ducts.

The 99km of high voltage cables was laid in 1100m sections.

This required the construction of 87 joints in 29 jointing bays.

Special joints were produced by dedicated production units of Nexans in Belgium and Switzerland; they use the very latest generation direct cross-bonding technology which is a cost-effective technique that prevents the loss of electric current in the screens across the joint.

To ensure the precision, quality and reliability of the joints, they were carried out by Nexans' highly skilled and experienced specialised jointing teams.

While working on this project, Nexans had to consider the high ground water level that is a characteristic of the coastal region, the possible presence of munitions from the First World War and the need to co-ordinate the work with other 36kV Elia installations in the region.

However, the greatest challenge was in laying the high voltage link under the Bruges-Ostend-Ghent canal.

Nexans was able to use an existing tunnel under the canal belonging to Aquafin.

Three 150kV cables were installed in this tunnel using the "snaking" technique in 25m deep vertical shafts and horizontally along an unbroken length of 115m without joints.

The cables were fastened to the tunnel wall using an innovative suspension system that does not require any drilling (a first for this type of cabling in Belgium) and were covered with a fire retardant protective coating.

Work on the project started in March 2005 and lasted for a year.

Elia will start using the new high voltage network from May 2006.

The dielectric tests at twice the nominal voltage (ie 174kV) were carried out successfully on the whole link and on the three phases of the 150kV cables.

This was carried out with a 440kV high voltage test installation in order to test the link in three parts.

A special test installation was designed by Nexans' Belgian team to reduce the cost of the tests, while also ensuring full conformity with Elia's strict technical and safety requirements.

In order to undertake the project, Nexans formed a consortium called Kust Energie Net (KEN) with Fabricom GTI and Visser and Smit Hanab.

The project was undertaken according to the ISO14001 directives, ensuring strict waste management and respect for environmental concerns in the coastal region.

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