For the maintenance of extra-high voltage overhead lines, transmission system operators (TSOs) normally have to shut down the line in question. This practice is more than understandable in view of occupational safety. On the other hand, it also reduces transmission capacity and increases the workload of the staff in the TSO’s network control centre who are in charge of coordinating the shutdown. An ideal solution must thus take both into account: first and foremost, the protection of employees and then the best possible utilisation of the facilities.
The Swiss TSO and TSCNET shareholder Swissgrid has carried out a pilot test on the 380kV line Chamoson-Romanel near Lausanne. At the beginning of October, just a few hundred metres from the Romanel substation and in the landing corridor of Lausanne-Blécherette airport, an orange signal ball was installed on the ground wire of the line, which had not been switched off beforehand. Swissgrid drew on the expertise and technology of Airtelis, a subsidiary of the French TSO RTE. Since the 1980s, Airtelis has been working on methods and technologies that allow maintenance work on extra-high voltage lines to be carried out safely and without switching off the power.
An Airtelis/RTE team of around 15 specialists travelled to the western Swiss canton of Vaud. An RTE helicopter also arrived on site, adapted to the work under voltage and equipped with various mirrors and an on-board camera. A special nacelle was attached to the helicopter with insulating anti-rotation ropes. Two Airtelis team members climbed into the nacelle to install the signal ball during the flight. They wore a suit specially designed for work under voltage, which protects its wearer like a Faraday cage. The installation work was carried out exactly as planned and was safely completed after 30 minutes. Swissgrid will now analyse the experience gained from this pilot project, in which the first maintenance work under voltage was carried out in Switzerland, and assess whether this technology should be used generally in future.