Cables that fly

Helicopter support is sometimes indispensable for stringing High Voltage lines.

From the early hours, everything is set at the big logistics car park in the Zubieta neighbourhood of Gipuzkoa. The Omexom Cantabria Líneas team is making its final preparations. Comprised of the Project Manager, a specialist foreman and 15 officials, plus an Occupational Safety technician, today is no ordinary day. Because today, visibility conditions finally prevail, the sun dispersing the final remains of mist that could have impeded the work, and they will be stringing a section of High Voltage (HV) line, with helicopter support.

As explains Luis Pérez, Project Manager, “the helicopter is used to assemble HV lines in exceptional circumstances, when human resources and/or other machinery are not sufficient. When assembling supports, for example when trucks and cranes cannot be transferred to a location due to the characteristics of the terrain, we use a helicopter for tower assembly and erection work. Or when there are lots of crossovers which would be very difficult to resolve using human resources alone”. On this occasion, there are many obstacles a deep valley with a steep slope through which the Oria river runs, two sections of motorway from the old Highway 1 on each bank, a medium voltage 30 KV line and lots of trees. Therefore, to string this double circuit line, a branch to the Zubieta substation for the 132 KV Hernani-Azpetia 1 and 2 lines, they opted for the only possible solution.

The preparations are now complete. Sara San José, Occupational Safety and Health officer at Omexom Cantabria Líneas, informs us that to prevent any items falling onto the road “they install posts and latticework on both sides of the road, joined together by nets. So that, should the cable descend, it doesn’t interfere with road traffic”. This is the most important aspect of the job in terms of safety, where participants are equipped with the corresponding PPE.

When the helicopter arrives, the pilot, his assistant and the people responsible for the work at Omexom Cantabria Líneas, hold a short meeting and immediately get to work. It’s not the first time they have done this sort of job. A small reel hangs from the helicopter’s fuselage to add weight and stability and avoid any rolling or movements that may pose a risk to the operators who have to attach the guide rope.

It’s a simple procedure. The helicopter, flying very slowly, will transport the guide rope from the last tower on the western side of the valley to the towers located on the opposite side. There, team members will have climbed to the top of the supports and, securely attached by fall arrest equipment, to help insert the ropes into the pulleys hanging from each transmission tower arm. At the end of the cable reel, a team will control the speed at which it is deployed, to avoid sudden snagging or drops that may cause it to catch on a tree or approach the latticework protecting the motorway.

Throughout the morning, the manoeuvre will be repeated up to 7 times, to install the guides for the six High Voltage connectors and a fibre optic cable. Carlos Landeras, the team foreman will maintain constant radio communication with the pilot’s assistant. They are responsible for hooking each of the ropes to the fixing point hanging from the fuselage. Then, once they achieve their objective, the pilot will release the rope from inside the vehicle. Landeras explains to us that “using a helicopter speeds up the work and makes it much easier. It reduces implementation times and also the risks involved compared to a manual intervention”.

From his privileged position, Landeras adjusts the speed at which the guide rope is deployed and is attentive to any possible incidents, such as ordering one of the officials to climb up to a pulley and reattach a fallen rope so they can continue with the work. Once the guide rope has been strung by the helicopter, continues Luis Pérez, “we use a pulling and winching machine on each side, and a brake to string the final cable, which is an aluminium conductor.”

To take advantage of the presence of the helicopter, once the work is complete in the Oria river valley, the entire team is transferred to another stringing location, an area with several hills and groves, where they get the job done in just a few minutes, work that Luis Pérez explains would have otherwise taken a couple of days, “manually pulling the guide rope, either by officials or using ground equipment”.

In about two months the work is completed for this new line, running 5.5 Km and including 20 supports with two 132 kilovolt circuits, a fibre optic line and steel ground cable, that will power the new Zubieta substation transferring energy from a future garbage incineration plant.

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