ULTRANET is a new, approximately 340 km-long high-voltage direct current (HVDC) transmission line between Osterath in North Rhine-Westphalia and Philippsburg in Baden-Württemberg. It is a project run by the transmission system operators Amprion and TransnetBW and will constitute what is known as a “multi-terminal”. The plan is to use existing tower systems for much of the line. Hybrid towers will be used, which can transmit both direct and alternating current on the same tower. The HVDC line will link together the three converter stations at Emden, Osterath and Philippsburg.

When it is finished, this “electricity highway” will mainly transmit renewable electricity from the north of Germany to the center and south from 2026 onwards, thus further advancing the energy transition in Germany.

Picture: © TransnetBW GmbH


So what is so special about ULTRANET?

The ULTRANET project is unique because many of the project components have never been implemented in this way before. The project also has many other special features. Below is a small excerpt:

  • ULTRANET is important because it is a European Project of Common Interest (e.g. similar to “Polder Rheinschanzinsel” for flood protection on the Rhine).
  • ULTRANET is sustainable because it provides hybrid HVDC transmission, meaning AC lines and the DC line largely share an existing overhead line route.
  • ULTRANET is innovative because its HVDC transmission uses full bridge technology, meaning that the DC voltage and the direct current can change their respective directions.
  • ULTRANET is future-oriented, as it is not only an HVDC transmission forming a multi-terminal HVDC system (three interconnected stations) with the A-North line, but also a cross-grid project with Amprion as project partner and later with TenneT.
  • ULTRANET is resource-friendly, as it involves construction of the first DC substation (converter station) on the site of a former nuclear power plant (Philippsburg).
  • ULTRANET is powerful. It is the most powerful self-commutated HVDC long-distance link in the world (2000 MW, up to 1470 MVA) at this voltage level (380 kV DC).
  • ULTRANET is variable because it can be used flexibly, e.g. for protection against grid failures. At the same time, ULTRANET could be the main player in a possible grid restoration.
  • ULTRANET is environmentally friendly because transmitting electric current using DC voltage results in minimal power losses.
  • ULTRANET supports the energy transition by offering the possibility to transmit renewable energy.

Technology subproject manager for the ULTRANET project at TransnetBW, Jiahua Weng, and me on the terrace of the info center at the site of the future direct current substation in Philippsburg in November 2022 (Picture: private)


My Diverse Range of Tasks in the ULTRANET Project

Fichtner has been supporting TransnetBW in this project since 2012. For me personally, ULTRANET started in 2013 with the preparation and review of design studies and the drafting of specifications. Some of the important questions that needed to be answered and for which solutions needed to be proposed were:

  • How far apart must an extra-high voltage AC and DC overhead line be if they are on the same tower?
  • How much additional extra-high voltage AC power can an existing extra-high voltage AC overhead line withstand?
  • What should a converter station located at the end of the line look like and how should it power itself?

In 2016, we helped select a suitable location for the converter station. Philippsburg was chosen and became the last exit, so to speak, on the electricity highway. We adapted the layout of the new buildings that had to be erected on the site to align them with the conditions on the site of the former Philippsburg nuclear power plant. This included the connection to the AC grid as well as the planning of the DC connection.

Since I have been involved in the project, I have experienced exciting changes time and again, which have resulted in new tasks for me. For example, it was initially planned to only make a connection between two stations, but this was revised and the third station became part of this initial planning as well, which in turn led to adjustments in the studies.

Starting in 2017, I took on further tasks that have since become part of my day-to-day work. These include review and quality assurance of the I&C and protection systems as well as the auxiliary power supply documents.

It is precisely this variety that I appreciate, as it makes the work exciting and interesting, and I am very proud to be part of this project. I am sure that this project, which is important in financial terms too, will go down in history as another milestone of German engineering.