Report by the Board of Management

Innovation above and below ground

The construction of new transmission connections increasingly prompts the question of whether they can be realised below ground. This is the wish of a public that is unenthusiastic about high-voltage pylons dominating the landscape. The 380 kV grid is fast becoming a grid for very large transmissions subject to stringent availability and controllability requirements. On account of the system risks TenneT has provisionally decided to install above ground the high-capacity transmission connections in the national 380 kV grid. But given the wishes of the public we quickly want to gain more experience with underground cable construction. The realisation of the 'Randstad 380 kV' connection offers a possibility to obtain such experience. A total of 20 kilometres of 380 kV dual-circuit connections will be cabled, divided in a South and North section. Overnight this will elevate the Netherlands to the position of a world leader in the underground construction of 380 kV transmission connections. This represents an important innovation that may provide a stimulus for placing high-voltage grids below ground. Together with Delft University of Technology and international partners, TenneT is drawing up a monitoring programme so as to track the behaviour of the system and to learn from the experience thus gained.

In 2008 the Dutch cabinet suggested placing a cap on the total number of kilometres of above-ground high-voltage lines. The Cabinet wants to include this cap in the Third Electricity Supply Structure Plan (SEV III) that is now on the parliamentary agenda. This means that for every new kilometre of above-ground line, the same length of high-voltage line must be installed below ground or combined with an existing high-voltage line. Compared with 220 kV or 380 kV connections, it is technically less complicated and far cheaper to install 110 kV or 150 kV lines below ground. TenneT preferably does this where it is relevant and efficient to do so, as in the case of difficult intersections with waterways, in the proximity of built-up areas and in areas of exceptional ecological value. In situations where the only option is to install lines above ground, TenneT will in the near future in principle use a new type of high-voltage pylon called Wintrack. The innovation lies in the considerable reduction of the magnetic field zone, thus significantly decreasing the utilisation of available space and leaving more space available for building.