Even if some of the gaps can easily be filled by the imagination of a non-specialist audience, the process of installing a conductor cable to attach it to an insulator on a pylon remains a highly technical operation. We will briefly explain this and introduce a technique that limits the risks to anything located below the route of an overhead line.

Installing a cable in several stages

When a line is erected, a nylon wire (3) is installed before the conductor itself is pulled across the pylons. This also makes it easier to pass the conductor from one pylon to another. The nylon wire is fed through pulleys larger than bicycle wheels (2) that are fixed under the insulators to help pull it from the first pylon to the last in the relevant section. The distance of a section varies from a few hundred metres to several kilometres. Once the wire has been connected to the second unwinding machine (4), it is linked to a second, thicker rope. This rope passes along the same route as the first wire until it can pull a steel cable strong enough to connect the conductor cable. The unwinding machine on the left in the second diagram holds the conductor in place and slows it down, while the one on the right pulls it along and ensures that the conductor remains taut and does not get too close to the ground. When the conductor cable is fully unwound, it is transferred from the pulleys and attached under the insulator. This operation is then repeated for each phase and for the overhead ground wire at the top of the pylon.

The same method is applied to replace conductor cables on an existing line, except that the old conductor cable is removed and coiled on one side as the new conductor is pulled across.

Beneath the lines, life goes on

You have probably noticed that Swissgrid’s extra-high-voltage lines systematically pass over infrastructure such as roads, motorways, railway lines and so on across Switzerland. How can we protect what lies beneath them? There are several solutions. The most widely known is to erect a gantry as shown in point (1). This system is particularly suitable when all the conductor cables are initially laid on the insulators or replaced. This type of operation involves multiple passages over the infrastructure and takes a considerable amount of time, which justifies the installation of bulky and sometimes costly protective equipment.

Keep rolling, little carriage

However, when replacing just one conductor cable or the overhead ground wire, there is a tool that helps save precious time whilst ensuring optimum safety: the «Rollenleine» carriage. But since a picture is worth a thousand words and a film is worth ten thousand, here’s the carriage in action on various lines.

When innovation reduces the price of your electricity

Although there is no compromise when it comes to safety or cost, another advantage of the «Rollenleine» method is that it costs less than installing protective equipment. It is expensive to block a road or a railway line, to put crews to work at night and to set up security installations. If this method continues to ensure optimum safety when lines are being installed or replaced, it will clearly become even more widespread and reduce the cost of this type of work.