Long distance tunnels for the installation of 400 kV XLPE cables

Open trenches with direct burial of power cables used to be the preferred installation technique in the city of Berlin over many years. This was true not only for low (1 kV) and medium (10 kV), but also for high (110 kV) and extra high (400 kV) voltage cable systems. Under the local conditions, i.e. mainly soft and sandy soil, this was proved to be the most economic construction method and, in most cases, there was sufficient space for open trenches. Of course, ducts or tunnels of up to some hundred meters were erected at special obstacles such as road or river crossings or where open trenches were forbidden due to environmental constraints. Only in the middle of the nineties, long distance tunnels for the accommodation of complete bulk power cable systems were taken into consideration. Eventually, the decision was made to build two tunnels of altogether 11.5 km between three major 400 kV/110 kV substations. The reasons for this decision, the technical aspects with the erection of the tunnels, the installation and arrangement of cables and auxiliary equipment and the operational concepts of the systems are described in this paper.