Above: The SuedOstLink


One of the German energy transition’s major grid expansion ‘corridor’ projects has taken another important step forward with confirmation of the underground XLPE cable suppliers for the 525 kV 2 GW SuedOstLink DC connection, which is around 500 km long and will link Wolmirstedt near Magdeburg in Saxony-Anhalt with Isar near Landshut in Bavaria. The transmission system operators TenneT and 50Hertz, who are jointly implementing the DC connection, have now awarded the contract to two cable manufacturers: NKT (which acquired ABB’s HV cable business in 2016) and Prysmian.

In addition to design and manufacturing of around 1000 km of XLPE underground cable, the scope also includes laying the cables, as well as installation of the connecting sleeves and terminations and the final high voltage test of the cable system. In addition, the suppliers are providing support in the detailed routing, specifically in determining individual cable lengths and locations of the connecting sleeves.

“We will use the innovative, plastic-insulated 525 kV underground cables for the first time worldwide,” said Tim Meyerjürgens, managing director of TenneT, “and will thus set new standards in technology and the reduction of environmental impact.” With the higher voltage level, the cables can transmit more power than conventional 320 kV cable systems of equivalent size. This requires fewer cables to transmit the same power so the route can be narrower and construction work decreased, with significantly reduced impact on the environment.

“The extensive tendering process that started in 2018 ends with the award of the contract; the two successful companies can now go into production and plan the cable laying, beginning in 2022. This is a good signal for the SuedOstLink joint venture project as well as for the energy transition across Germany and Europe”, said Dr Frank Golletz, technical director at 50Hertz.

NKT is supplying the underground cables for the northern part of the SuedOstLink project through Saxony-Anhalt, Thuringia and Saxony. Prysmian is producing the underground cables for the Bavarian SuedOstLink section.

All bidders had to demonstrate the performance of their cables in a prequalification test. The 12 month trial simulated the expected operational load over the planned total operating life of around 40 years. On the basis of positive test results, the transmission system operators decided on the system voltage of 525 kV last year. Until then, a voltage of 320 kV was considered in the planning process.

The SuedOstLink is currently undergoing the planning approval procedure. At the end of this procedure the Bundesnetzagentur (federal network agency) will finalise the exact route of the underground cable.

SuedOstLink is expected to be completed by the end of 2025.

TenneT and 50Hertz are investing around five billion euros in the SuedOstLink project, amortised over 40 years, but the project is expected to save around 1.3 billion euros annually in national grid stabilisation costs, which are borne in full by electricity consumers. These grid stabilisation measures are necessary because the existing German power grid is not  designed for the growing share of renewables. energy resources in power generation.

The SuedOstLink is an EU “Project of Common Interest” and is receiving support within the “Connecting Europe” framework. Since 2012, the need for it has been repeatedly confirmed in successive German grid development plans. The link will connect the north-eastern German states, with their high wind and solar power generation levels, to the industrial regions and big power consuming centres of Bavaria.

Offshore plans

TenneT is also planning to use 2 GW 525 kV HVDC links for offshore wind farms. It has recently announced the launch of an “innovation partnership” to develop two 2 GW HVDC connections, with converter platforms of a new design, for first deployment in the Dutch IJmuiden Ver wind farm zone, due to enter operation before 2030.

TenneT descibes an innovation partnership as “a tendering procedure in which TenneT, as contracting authority, can start a development process together with suppliers and then proceed to purchase the solution that is not yet available on the market.”

About 40% of the Netherlands’ electricity needs will come from offshore wind farms by 2030, it is estimated, and it falls to TSO TenneT to implement the required grid connections. The two 2 GW HVDC links would be in addition to eight new 0.7 GW AC grid connections already planned by TenneT for Dutch waters.

TenneT says it has entered into the HVDC innovation partnership with its suppliers “to ensure that this technically advanced and innovative requirement will connect seamlessly with what they can develop and manufacture.”

“Given the combination of the large distance to the coast and the size of the IJmuiden Ver wind energy area, a 2 GW HVDC solution, based on 525 kV, appeared to offer the best economics”, said TenneT. In particular, “it requires only one cable system per 2 GW, limiting the impact on the environment and the surroundings.”

The five suppliers in the innovation partnership involved in the design phase of TenneT’s 2 GW 525 kV offshore HVDC system are: ABB Power Grids (in the process of being divested to Hitachi); GE Renewable Energy’s Grid Solutions (Netherlands); Consortium Global Energy Interconnection Research Institute Co Ltd (GEIRI) & C-EPRI Electric Power Engineering Co Ltd (C-EPRI) (China); Siemens (Germany); and Xian Electric Engineering Co Ltd (China).

The suppliers will work to “criteria set by TenneT” and transfer information to Iv-Offshore & Energy BV, which is carrying out the front-end engineering design study on behalf of TenneT.

The plan is to develop “a standardised platform design for all HVDC solutions” based on what TenneT describe as “the joint R&D innovation phase.” The final standardised platform design will be used for at least three new offshore HVDC links in German waters (including LanWin and BalWin), as well as IJmuiden Ver Alpha and Beta, contributing to reduced offshore grid costs.

New cable standard

As well as the five suppliers working on the new HVDC converter platform, TenneT has also contracted eight cable suppliers to develop a new standard for the associated submarine cable system. “A 525 kV HVDC extruded submarine cable system with 2 GW capacity is currently not implemented in any project worldwide”, notes TenneT. The cable development programme should result in a certified cable system which TenneT can apply in the IJmuiden Ver, BalWin and LanWin projects as well as other projects using the same power output and voltage. “This will reduce costs and minimise spatial impact.”

The participating cable suppliers are: Hellenic Cables SA (Greece); LS Cable & System Ltd (Korea); Nexans Norway AS (Norway); Ningbo Orient Wires & Cables Co, Ltd (NBO) (China); NKT HV Cables AB (Sweden); Prysmian Powerlink Srl (Italy); Sumitomo Electric Industries, Ltd (Japan); and Zhongtian Technology Submarine Cable Co, Ltd (ZTT) (China).

“It is very positive to see that multiple international cable suppliers are participating in this programme”, says Marco Kuijpers, director of offshore projects at TenneT. “It shows that the sector is keen to innovate together to produce a new standard for submarine cable systems, substantially reducing costs for society.”

This new cable will connect the 2 GW platforms to the land station. To transport the required 2 GW of power, a submarine cable system operating at 525 kV DC employing extruded insulation is needed. TenneT expects that the certified cable system will be available by spring 2022. The development programme will “enable both the developers and TenneT to deliver a new cable system cost effectively and on time”, the TSO believes. “The need to develop this submarine cable system is derived from the expectation that it will reduce manufacturing and installation costs. Not only for the cable system itself but also for the entire grid concept, including the HVDC offshore platform and the HVDC land station.” TenneT say it “expects the bundled installation to achieve significant cost reductions.” As well as reducing installation costs, it is “also expected to reduce dredging costs because all cables can be put in a single trench.” The new technology also “results in fewer platforms and land stations, which “is not only interesting in financial terms” but also reduces environmental impacts.

The move to standardised 525 kV 2 GW connections builds on TenneT’s extensive experience with offshore HVDC grid connections in Germany, as well as with HVDC interconnectors, for example its Germany/ Norway NordLink subsea project, which employs 525 kV (1400 MW).

TenneT says the HVDC standardisation intiative “fulfils its responsibility as grid operator of the offshore grid, by stimulating innovative solutions that contribute to rolling out a cost-efficient and future-proof offshore grid infrastructure.”