Frequently Asked Questions - Projects

An overview of frequently asked questions about our projects.

A new national policy document for the supply of electricity (SEVIII) has been issued, in which it is stipulated that the total length of overhead high-voltage connections shall not increase resulting from the realisation of the new connections of 110kV and higher. What does this mean?

The new schedule indicates that the number of kilometres of high-voltages lines is not permitted to increase in the future. Of the total electricity grid in the Netherlands, from power plant to socket, approximately 97% of the cables is underground, being a total of approximately 260,000 km. Only the more heavy transmission and distribution lines (approximately 9,000 km) are installed as overhead lines. The government has now decided that the total length of overhead lines is not permitted to increase any further. If a new connection is to be made, this will need to be implemented by means of an underground cable, or the same length of existing overhead line should be removed at a different location or it should be installed in combination with an existing overhead cable.
It is beyond dispute that the reliability of electricity supplies continues to be at the centre of attention.

How will it be determined?

At present the policy is implemented in further detail. There will be an answer to questions such as: Under which circumstances will underground cables be installed? Where will this be? Within which time period will this be implemented? What are the (environmental) effects thereof on the subsoil? These questions will now first be thoroughly investigated. The principles stipulated in the SEV will function as the starting points. The consideration for overhead or underground lines will mainly relate to: the costs, technical insecurities, landscape, nature, archaeology and ecology, scope of the space involved and land-use planning, quality of the living environment and (ground) water management.

What are the differences between overhead and underground?

An overhead connection is cheaper, can be maintained well and is visible. Restrictions with regard to works in the direct surroundings of the overhead lines – related to the high-voltage lines – are applicable. As such it is not permitted to build high-rise buildings near high-voltage lines, however the land is permitted to be used for agriculture or nature recreation. With regard to underground lines a strip of land neighbouring the line or cable should remain free of activities, as the grid manager should have free access to the cable at all times.

Currently only a limited number of kilometres of underground lines are in place. Is it complex to install these cables?

Almost the entire TenneT high-voltage grid is represented by overhead lines. Even on an international scale it is only very seldom that specifically 380kV cables are installed underground. This is not only due to the costs involved, technical disadvantages of the underground installation of 380kV play an important role as well. This could be of influence to the stability of the complete electricity grid, which would require significant compensation measures. Moreover, repair of failures involves more time (2-20 days) when compared to an overhead line (8- 48 hours). In the Netherlands the water crossing below the Nieuwe Waterweg is currently the only underground line. In a technical sense it is easier to install 110kV or 150kV connections underground. This procedure is currently implemented much more often. An example thereof is the installation of an underground line between Haaksbergen and Hengelo in 2008/2009.

Who decides whether a line will be installed overhead or underground?

This depends on the project. In projects which are of national interest, the national government will decide, such as in relation to the Randstad 380kV. At this time the government makes a selection based on all possibilities. In most cases the Dutch regulator DTe is involved as well. After all, they need to approve all investments. For each project a detailed consideration is made with regard to the costs, technical insecurities, landscape, nature, archaeology and ecology, scope of the space involved and land-use planning, quality of the living environment and (ground) water management in relation to granting a permit.

Is TenneT actively involved in the installation of underground lines?

TenneT is active with regard to innovative developments, involving overhead lines as well as underground lines. As such TenneT has developed a pylon with a low magnetic field, which can easily be integrated in the landscape. Furthermore TenneT participates in a number of study groups in order to further develop the installation of underground lines. For example, TenneT is associated with the independent Dutch knowledge centre for underground construction (COB). They jointly work on a further development of the policy for underground or overhead lines.

What are the costs involved?

It is complex to indicate what the exact costs for the underground installation are. It all depends on a numbers of factors such as the specific area, type of connection and technical possibilities. In general it can be indicated that the underground installation of 380kV-connections is 4 to 8 times more expensive per kilometre than for an overhead line.

Who will pay the costs?

This also depends on the situation. In most cases the costs related to the Dutch national transmission grid for electricity are socialised. This means that these costs will be incorporated – via the transmission costs - in the price for electricity. In effect these costs are paid by all electricity users. However, it could also be that a specific company or municipality pays for the underground installation of (a section of) an existing high-voltage line.

Do underground lines or connections have magnetic fields as well?

The current public assumption is that underground lines have no magnetic fields. This is an incorrect assumption; however the shape of the field differs from the magnetic field applicable to overhead lines. The width of the magnetic zone related to underground connections is somewhat narrower; however, it is somewhat higher immediately above the lines. For this reason it could be that in densely populated areas (such as in de Randstad) underground lines could be preferred in order to allow building areas closer to the connection, whereas in other areas the installation of underground lines would have no advantages with regard to magnetic fields.

Why is an extra line being created in the Randstad region?

The construction of this line will create two ring-shaped high-voltage grids, one in the southern and one in the northern part of the Randstad region. This will strengthen the infrastructure. Both rings will also be connected to the national high-voltage grid. Investments in the upgrading of transmission capacity are necessary to continue safeguarding the security of supply and to improve the reliability of the system.

Further information can be found at 'Projects/Randstad380'.

What is the purpose of the North Sea interconnection to Norway that is being installed?

Of all electricity produced in Norway, 99% is generated through hydro‑electric power. It is partly owing to this fact that the new interconnection will result in more stable and lower prices on the Dutch market. Furthermore, it will boost the security of supply in both countries, enhance free market operation and improve the liquidity of the Dutch market. Electricity can be transmitted in both directions, depending on demand and supply. In the Netherlands electricity is mainly generated by means of fossil fuels such as natural gas and coal.

Our expectation is that the Dutch power plants will be able to operate more efficiently thanks to the NorNed cable. Especially at night they will be able to supply electricity to Norway so that less water has be taken from the Norwegian reservoirs. This water can instead be used for the daily peak load in the Netherlands. For this reason we are working on the 'NorNed' project. The Scandinavian and Dutch electricity markets will be linked through the electricity exchanges APX and Nord Pool Spot. The projected gains resulting from price discrepancies between the two markets would render the cable a financially feasible option.

Further information can be found at Projects/NorNed.

Why aren’t all TenneT’s lines installed underground?

It is generally more expensive to drill boreholes and install lines underground, and the projects must usually be funded by the government (i.e. using share capital).

In what way does the Wintrack project lead to innovation?

Wintrack is a new concept, developed for high-voltage lines with a much smaller magnetic field than existing lines. The pylons used are largely made of synthetic materials and only contain limited quantities of metal. This is an important development because the Ministry of Housing, Spatial Planning and the Environment (VROM) wishes to adopt a stricter directive regarding magnetic fields, which extends the area around high-voltage lines where the construction of new buildings is prohibited. The new directive also restricts the scope for installing new lines. With respect to 380 kV high-voltage lines, the new directive stipulates that no new buildings may be erected in an area of approximately 300 metres around these lines. If the Wintrack concept is applied, the restricted area will only measure 75 metres.

Further information can be found at Projects/Wintrack.