German field report on underground cabling

07.10.2020

The use of underground cables for power transmission in the extra-high voltage three-phase current range is partly still uncharted technical territory for the four German TSCNET shareholders 50Hertz, Amprion, TenneT, and TransnetBW. As most projects are in the planning, approval, or construction phase, no partial earth cabling project is yet in full system operation, let alone a project with exclusive cabling. However, Tennet has commissioned the Wilhelmshaven-Conneforde line as recently as last week: It is the first 380kV line with underground cable sections in three-phase technology connected to the meshed power grid by the Dutch-German transmission system operator (TSO).

To inform politics and public about the current status of underground cabling in the national transmission system, the four German TSOs have, at the request of the German Federal Ministry for Economic Affairs and Energy, jointly prepared a field report on the use of underground cables in the extra high-voltage three-phase current range. The 65-page report examines seven different key issues in respective main chapters, covering technical, administrative, economic, environmental, and social aspects: dialogue and acceptance, approval procedures and the environment, design and construction, operation and operational safety, underground cable technology, systems engineering, and finally economic efficiency. Key findings of 50Hertz, Amprion, TenneT, and TransnetBW can be summarised as follows:

  • Partial underground cabling does not per se lead to a greater acceptance of line construction projects – compared to the construction of overhead power lines, the concern merely shifts from the residents mainly to landowners and farmers.
  • As far as planning, approval, and construction times are concerned, current experience shows that partial underground cabling requires at least one to two years more than overhead lines. More extensive implementation planning, intensive soil investigations, and negotiations with the owners consumed a great deal of time in the pilot projects. The construction itself is also more complex due to the necessary crossing of infrastructures, 40 to 60-metre-wide aisles, and major interventions in the soil ecosystem.
  • Regarding operational and system safety, underground cable installations have a lower availability rate than overhead lines, as repair times are significantly longer in case of damage. Moreover, with an increasing share of partial underground cabling, the complexity of grid operation and thus the risk to system stability also rises.
  • In terms of economic efficiency, the costs of partial underground cabling are significantly higher than those of overhead lines, and this applies to planning, construction, and operation. Depending on the project-related terrain and soil conditions, the investment costs are usually six times higher.

The four German TSOs have published their joint “Field report on the use of underground cables in the extra-high voltage three-phase current range” (picture: TenneT)

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> See TransnetBW news release, in German (html)
> Open Field Report, in German (pdf, 2.9MB)

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Wilhelmshaven-Conneforde line put in operation

05.10.2020

With the Wilhelmshaven-Conneforde line, the Dutch-German transmission system operator (TSO) TenneT has commissioned an important grid expansion project for the German and European energy transition. The 380kV line from the new substation Fedderwarden near Wilhelmshaven on the German North Sea coast to the Conneforde substation in Ammerland, both in the federal state of Lower Saxony, is not only crucial for the transmission of mainly wind power and electricity from regional generators, but also for strengthening security of supply in northern Lower Saxony. Furthermore, it represents a novelty for the TSCNET shareholder in terms of technical implementation: “With this new line, we have put into operation the first pilot project with two underground cable sections in three-phase technology and connected it to the meshed power grid in Germany,” explained Tim Meyerjürgens, COO of TenneT.

The commissioning ceremony on 2 October 2020 in Fedderwarden was attended by representatives from politics, including Andreas Feicht, State Secretary at the German Federal Ministry for Economic Affairs, and Energy and Olaf Lies, Minister for the Environment, Energy, Construction, and Climate Protection of Lower Saxony. The new line is only about 30 kilometres long, but – together with the new construction of the Fedderwarden substation – “of great importance for the entire European electricity trade”, commented Olaf Lies. The Minister was impressed by TenneT’s latest milestone in the energy transition. State Secretary Feicht referred to the newly gained potential for integrating large amounts of wind power into the German electricity market and the technical relevance of the pilot project: “Knowledge obtained in such pilot projects about the construction and operation of the technology will be of great benefit for further power grid expansion in the future.”

The line project was successfully completed after less than two years of construction. Almost 5 kilometres of the line were implemented as underground cables. However, even if TenneT can be satisfied with what has been accomplished so far and is strongly committed to expanding the transmission of green electricity throughout its entire grid area, Meyerjürgens sees a need for further action, especially in view of the increasing offshore wind volumes: “Still, we already see today a further demand for expansion in the Wilhelmshaven and Friesland region.”

TenneT commissioned the new Wilhelmshaven-Conneforde line (picture: TenneT)

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> See TenneT press release, in German (html)

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Tunnel drilling for last section of the Nant de Drance connection

03.10.2020

The Nant de Drance pumped storage power plant in the Swiss canton of Valais is one of the most powerful power plants of its kind in Europe, generating around 2.5bn kWh per year, when it goes fully operational in 2021. The plant has been commissioned successively in sections in recent years. TSCNET shareholder Swissgrid, the Swiss transmission system operator (TSO), is responsible for connecting the power plant to the extra-high voltage grid and for transmitting the hydropower to urban areas in Switzerland. Two of the three sections of the extra-high voltage link to Nant de Drance – an underground cable of 6.5 kilometres between the power station and the Châtelard substation via the access tunnel of the plant and an overhead line of 12.5 kilometres between the Châtelard and La Bâtiaz substations – have been in operation since the end of November 2018.

Tunnel boring has now begun for the third and final section between the substations of La Bâtiaz and Le Verney, which belongs to the municipality of Martigny. The mini tunnel boring machine, weighing around 60 tonnes, was traditionally given a female name on 2 October 2020 at the construction site in Le Verney and will in future be known as Giorgia. Shortly after its christening, it was lowered into the shaft, where it will take around eight months to dig and secure the tunnel between the substations. The tunnel will have a diameter of 2.5m and is dug 12 to 20m deep into the ground. Giorgia is controlled entirely from the control centre at the construction site in Le Verney.

Construction of the underground cable link commenced in June 2020 with the excavation of the shaft at Le Verney and will take two years. The shaft at La Bâtiaz will be dug at the same time as tunnelling work. The finishing work in the tunnel will follow from summer 2021, after which the gantry to connect the Nant de Drance link to the 380kV Chamoson-Romanel overhead line in Le Verney will be built. Finally, the cables will be laid in the tunnel. Commissioning of the 1.2km long underground line is scheduled for 2022. Nant de Drance is already now connected to the transmission grid even before the last section of the link is commissioned: An interim solution was introduced in 2019 by increasing the voltage of one of the two overhead lines between La Bâtiaz and Le Rosel to 380kV.

Swissgrid has started tunnel drilling for the final section of the connection of Nant de Drance to the national 380kV grid (picture: Swissgrid)

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Network Agency decides on southern routing of SuedLink

25.09.2020

700 kilometres of underground cable to be laid and an investment volume of around €10bn – this makes the 525kV line SuedLink the largest and probably most important individual project of the energy transition in Germany. The exclusive use of underground cables in the project is politically specified to increase the acceptance of the project by the population: For only if one succeeds in effectively connecting the windy regions of northern Germany with the centres of consumption in the industrially highly developed south and west via such “electricity highways” as SuedLink, the German – and European – climate targets can be achieved.

SuedLink is jointly implemented by the two TSCNET shareholders TenneT, the Dutch-German transmission system operator (TSO), and TransnetBW, the TSO from southwest Germany. The project is making step-by-step progress in the regulatory, planning, and implementation areas. This year, for example, regional planning offices have already been set up and the contracts for the cables awarded. Now the competent government authority, the Federal Network Agency (Bundesnetzagentur), has decided on the southern section between the Lower Franconian Arnstein near Schweinfurt and the Großgartach substation in the Stuttgart Metropolitan Region (SuedLink section E). This 137 kilometre long section runs through the control areas of both TSOs involved.

The Bundesnetzagentur’s decision largely follows the proposal by TenneT and TransnetBW, according to which the Würzburg metropolitan area is largely bypassed in the west. The proposal of the two TSOs had already incorporated the results of the application conferences and requirements of the Bundesnetzagentur. The last 16 kilometres to the Großgartach substation are a special construction feature. Here an existing salt mine is to be used for an underground course of the cable project. This increases construction costs, but these are outweighed by other benefits, in particular the reduced impact on the environment and residential areas. After the completion of the federal sectoral planning for the SuedLink section E, planning approval procedures are to follow which will determine the exact route of the line within the corridor and the technical implementation.

The German Federal Network Agency has decided on the southern section of the SuedLink power line, a joint project of TenneT and TransnetBW (picture: TenneT)

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> See press release by Bundesnetzagentur, in German (html)

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ALEGrO on the final straight

17.09.2020

Lichtenbusch near the westernmost German city of Aachen is located directly on the border between Germany and Belgium and is divided into a Belgian and a German part. Right here, on 16 September 2020, the final joint of the “Aachen Liège Electricity Grid Overlay” (ALEGrO) was installed by TSCNET shareholder Amprion, one of the four German transmission system operators (TSOs), and its Belgian partner TSO Elia. Over a distance of 90 kilometres, the DC interconnector with a transmission capacity of 1,000MW connects the Oberzier substation in the German Rhineland region with the Elia substation in Lixhe in the Walloon province of Liège. ALEGrO is the first direct link between the Belgian and German electricity grids and was realised over its entire length by means of underground cables.

The European Project of Common Interest (PCI) provides much needed grid capacity for cross-border electricity flows, while strengthening security of supply in the German region of Aachen-Cologne and the Belgian province of Liège. The cable laying work for ALEGrO started in October 2018 and after twenty months of construction, the civil engineering work was concluded in June 2020. Despite the Covid-19 pandemic, ALEGrO is thus on schedule and nearing completion. The binational power bridge will go into technical operation in October 2020 and will be available to the European electricity market from mid-November. The technical integration of the DC cable into the three-phase grid is a step by step process. The same applies to the parallel market integration. Here, day-ahead capacities are offered first followed by intraday capacities. The allocation of long-term capacities will start in early 2021.

Amprion and Elia installed the final link of the ALEGrO interconnector, which will go into technical operation soon (picture of the project managers Ingo Sander, Amprion, and Dirk Wellens, Elia: Amprion)

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New power line for west-central Switzerland

17.09.2020

Switzerland’s national sustainable energy strategy and the resulting growth in hydroelectricity generation in the cantons of Berne, Valais, and Ticino require a significant increase in electricity transmission capacities, particularly to transport green energy to the Swiss Central Plateau and to ensure long-term security of supply throughout the country. This requires the upgrade of existing lines to 380kV and the construction of new high-capacity lines. One example of this is the 220kV line from Innertkirchen in the district of Interlaken-Oberhasli (canton of Bern) to Ulrichen/Obergoms in the district of Goms (canton of Valais), most parts of which are over 60 years old.

To maintain a secure connection between Haslital and Obergoms in the future, the Swiss transmission system operator (TSO) Swissgrid has developed various planning corridors for the construction of a new extra-high voltage line and submitted them to the Swiss Federal Office of Energy (FOE). The TSCNET shareholder has defined three main corridors, some of which include sub-corridors: The first option is a pure overhead line, which crosses high alpine terrain in parts. The second is partial cabling. Here, the middle section is implemented as underground cables, mainly in existing tunnels up to Obergoms. The third variant provides for underground cabling almost exclusively. Either in a new, yet to be built tunnel and then, as in the second alternative, in largely existing tunnels – or in the proposed multifunctional Grimsel Tunnel (envisaged for rail transport and power transmission). If the tunnel is used, the corridor variants for the last section to Ulrichen are possible as overhead line or underground cable        .

Each of the submitted options has specific advantages and disadvantages in terms of spatial planning, environment, technology, and economic efficiency. What they all have in common is the relief of settlements in the affected area, where overhead lines currently run partly through villages. The FOE is now discussing and evaluating the planning corridors. Its recommendation will then be submitted to public consultation, and the Swiss Federal Council is expected to determine the planning corridor and transmission technology between Innertkirchen and Ulrichen at the end of 2022.

Swissgrid has designed and submitted corridor variants for the new Innertkirchen-Ulrichen 380kV line (picture of the existing line: Swissgrid)

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TenneT continues offshore cost reduction with BorWin5

12.08.2020

BorWin5 is to become the 15th offshore grid connection system implemented by the Dutch-German transmission system operator (TSO) TenneT in the German North Sea, the twelfth DC connection, and the fourth offshore grid connection off the coast of the island of Borkum using HVDC transmission technology. With a total length of 230 kilometres, BorWin5 will also be the longest offshore connection of the TSCNET shareholder. The realisation of BorWin5, expected to be commissioned in 2025, is progressing well, as TenneT has now placed orders for the construction of the onshore and offshore converter stations as well as for the production and installation of the DC underground and submarine cables. The contract for the converter stations has been awarded to a consortium of Siemens and Dragados Offshore and for the cables to NKT HV Cables.

The key technical data of BorWin5 reflect TenneT’s extensive experience and expertise in the offshore sector on the one hand, and the TSO’s commitment to constantly improving established technology on the other. For example, BorWin5 is the second project, after DolWin5, in which the wind turbines are connected directly to the corresponding offshore platform via 66-kv three-phase power cables. This dispenses with, among other things, the transformer stations otherwise required in wind farms. With this direct connection, BorWin5 represents the new generation of cost-efficient offshore connections. Moreover, with BorWin5’s smart platform concept, the TSO is advancing standardisation further by installing only such technology on offshore platforms as is absolutely necessary on the offshore side.

Tim Meyerjürgens, COO of TenneT, emphasises the company’s continuous cost reduction in the construction of offshore grid connection systems – a highly significant aspect for the success of the energy transition – and the specific cost efficiency of BorWin5: “Compared to the predecessor project DolWin5, we were again able to achieve a significant cost reduction for the converter stations. One reason is that for BorWin5 the smart platform concept is being used for the first time. This not only keeps the costs for the platform construction manageable, but also allows us to extend the intervals for maintenance and servicing to once a year.”

TenneT awarded contracts for the on- and offshore converter stations as well as the underground and submarine cables for BorWin5 (picture shows the preparatory horizontal drilling for BorWin5 on Norderney in 2019)

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TenneT to invest up to €5bn p.a. for the energy transition

31.07.2020

The Dutch-German transmission system operator (TSO) TenneT has just published its first-half 2020 report. Needless to say, the second quarter of 2020 was characterised by the corona pandemic and the extensive measures taken to ensure a safe and healthy working environment, but despite this, the TSO has made significant progress in developing the transmission grid onshore and offshore and in integrating growing amounts of renewable electricity. At the same time, TenneT has maintained a high level of supply security of 99.99% for 42m end consumers in Germany and the Netherlands.

As Europe’s first cross-border TSO, TenneT promotes the European market integration. The TSCNET shareholder increasingly benefits from its binational integrated approach to grid planning, management, and operation. Manon van Beek, TenneT’s CEO, comments: “Sharing best practices and lessons learned between our German and Dutch operations is paying off more and more in terms of an integrated approach to offshore and onshore grid expansion, better grid utilisation due to European innovations and cross-border energy system planning.”

TenneT currently operates 14 offshore grid connections, twelve in the German and two in the Dutch North Sea. The twelfth offshore grid connection in Germany, BorWin 3, was handed over to TenneT in the first half of 2020. In Dutch waters, the Borssele Alpha grid connection recently transmitted offshore wind power for the first time and the Borssele Beta grid connection has now been commissioned well ahead of schedule. While in the offshore sector experience from the German market is used for the Dutch, the situation is the other way round when it comes to underground cabling. Here, expertise from the Dutch Randstadt project is applied for the DC connections SuedLink and SuedOstLink. These two largest projects of TenneT, which are being entirely installed underground, will be essential for the transmission of wind energy from northern to southern Germany.

Such efforts require huge investments – facilitated by solid financial results: The underlying operating result (EBIT) increased to €414m in the first half of 2020. During the same period, investments in the German and Dutch high and extra-high voltage grids also increased by approximately 30% compared to the first half of 2019, but will do so much more in the future. TenneT expects a further rise in the annual investment volume to €4 to 5bn in the next years. Otto Jager, CFO of TenneT, explains: “We are going to connect growing amounts of renewable electricity to the grid while facilitating the development of a borderless European electricity market. In light of future equity funding needs, the ongoing talks with the German government about a possible equity participation, next to the Dutch State, are welcomed by TenneT.”

TenneT presents Half-year Report 2020 (picture: TenneT)

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Construction permit for Pradella-La Punt

13.07.2020

As the extra-high voltage line in the Swiss Engadine between Pradella and La Punt constitutes a bottleneck in the Swiss and pan-European transmission system, the Swiss transmission system operator (TSO) Swissgrid has long aimed to increase its transmission capacity to 2 x 380kV. This will improve import capacity and security of supply in the canton of Graubünden and facilitate the transport of Engadine hydropower. The project is part of the “Strategic Grid 2025”, Swissgrid’s ambitious modernisation and expansion plan.

The Swiss Federal Inspectorate for Heavy Current Installations (Eidgenössisches Starkstrominspektorat-ESTI) now has approved the reinforcement and new construction of pylons between Pradella and La Punt. Swissgrid has already refurbished the pylon foundations in the past two years, so that work can commence soon. Approximately 3500 tonnes of steel will be needed to upgrade the around 50-kilometre-long overhead line. The construction will be carried out in two sections and is expected to be completed by the end of 2022.

To reduce the overall environmental impact in the region, Swissgrid is supporting a local grid operator in replacing a 60kV overhead line with a 110kV underground cable. As a result, 1100 pylons will be disappearing from the landscape.

Swissgrid can start with the 2 x 380kV upgrade of the Pradella-La Punt line (picture: Swissgrid)

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Contracts for 525kV SuedLink cables

29.06.2020

SuedLink is evolving in major steps this year. The DC line – realised jointly by the two TSCNET shareholders TenneT, the Dutch-German transmission system operator (TSO), and TransnetBW, the TSO from southwest Germany – is the largest and probably most important single project of the energy transition in Germany. With around 700 kilometres of underground cable to be laid and an investment of around €10bn, SuedLink will connect the windy regions of northern Germany with the centres of consumption in the industrially highly developed south and west. In February 2020, the Federal Network Agency (Bundesnetzagentur) initiated the plan approval procedure for the first SuedLink sections, in May the orders for the regional planning offices were placed and now TenneT and TransnetBW have awarded the contracts for the plastic-insulated 525kV underground cables – in parallel with the ongoing approval procedures.

NKT and Prysmian PowerLink have eventually been selected as providers for the SuedLink cables, with a total order value of approximately €2bn. The contract comprises design, manufacture, supply, laying of the underground cables, further installation work, and the final high-voltage testing of the cable system. Both companies have demonstrated their expertise in numerous international connection projects on and offshore, and both have proven the quality of their cables in extensive prequalification tests with several cable manufacturers in a multi-year test phase. They were also commissioned for the German affiliate project, SuedostLink, by the two TSOs 50Hertz and TenneT.

TenneT and TransnetBW chose plastic-insulated underground DC cables with a voltage level of 525kV because they transmit more power compared to a 320kV solution and only require half as many cables. Less transmission loss and less civil engineering work translate into both, financial benefits for the TSOs and minimal environmental impact. TenneT Managing Director Tim Meyerjürgens comments: “In the future, SuedLink will form the backbone of the energy transition in Germany. With the commissioning of the DC ground cables, we are now moving from the planning stage to the realisation of this important power link.” Dr. Werner Götz, Chairman of the TransnetBW Executive Board, adds: “We are very happy to be able to apply this innovative and environmentally benign technology for SuedLink.”

TenneT and TransnetBW awarded the contracts for the 525kV DC underground cables for the SuedLink power highway (picture: TenneT)

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> See TenneT press release (html)
> See TenneT press release, in German (html)
> See TransnetBW press release (html)
> See TransnetBW press release, in German (html)

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