August 16, 2022
9 min read

A power woman for a Herculean task

Christina Hümmer

Her team’s innovations in direct current are helping to realize a monumental feat of electrical engineering being built on the Spanish coast: the first offshore converter platform equipped with new gas-insulated direct current switchgear.

The coasts of Southern Spain have been one of the mythical sites of civilizations since time immemorial: The Greek demigod Hercules himself is said to have founded the coastal city of Cádiz, near the Strait of Gibraltar.

If you turn your gaze to the east in the picturesque old town of Cádiz, you may catch sight of a huge steel structure on the horizon – the result of a truly Herculean task of technological superlatives. It’s here where Spanish EPC contractor Dragados Offshore S.A. and Siemens Energy are building the DolWin kappa converter platform.

DolWin kappa is the centerpiece of TenneT’s, in the EU leading green offshore grid operator, DolWin6 grid connection system, a 900-megawatt link that will ensure TenneT, transmission system operator of the high-voltage grid in the Netherlands and large parts of Germany, can transport offshore wind power from the German North Sea to shore. Once commissioned, the platform will rise some 56 meters out of the North Sea – the height of an 18-story building. Its total weight of 11,000 tons supported by 10 steel piles anchored up to 50 meters in the seabed.

We're talking about up to 15,000 components in 200 subsystems that must be integrated.

Maria Kosse

Lead Engineer HVDC, Siemens Energy

DolWin kappa will receive the alternating current from several wind farms and convert it into direct current. This is the only way to transport the electricity over 90 kilometers to the grid connection point onshore with as little loss as possible. There, it will be converted back into alternating current by a second converter station so that the electricity can be fed into the grid and transported to households.

It's a complex interplay of a wide variety of power transmission technologies: "We're talking about up to 15,000 components in 200 subsystems that must be integrated,” says Dr. Maria Kosse from Siemens Energy. As a lead engineer working on grid connection systems, her job is to make sure that every component in the converter platform perfectly interacts. From the heart of the converter platform, the high-voltage direct current transmission (HVDC) converters, to the brain of the platform, the control & protection systems that have to process approximately 400,000 signals, every function and every technology must run properly to bring green energy to every household. However, it’s not the brain or the heart of the converter platform, but a different technology that makes Maria's eyes light up.

Maria shows the inside of the DolWin kappa converter platform. In August 2022 it started its journey to the North Sea. As part of a 900 megawatt grid access system it will supply more than one million households in Germany with green wind power.

In DolWin kappa, a direct current gas-insulated switchgear (DC GIS) is being used offshore for the first time worldwide. Responsible for the development of switchgear up to ±550 kV, Maria accompanied the DC GIS from an early stage in 2016 until its successful commissioning test in the Cádiz dockyard in 2021.

For the connection of offshore wind farms, where space is at an absolute premium, the DC GIS brings a decisive advantage: While comparable air-insulated switchgear in standard configuration would require 4,000 cubic meters, the DC GIS requires only 200 cubic meters. What’s more, it doesn’t even require a dedicated room on platforms but can simply be added into another technology’s room.

With space requirements reduced by up to 95 percent, Maria and her team have broken new ground in insulation technology to provide one of the most space- and therefore cost-saving technologies in grid access for offshore wind, making it possible to build converter platforms like DolWin kappa in the most compact way, saving valuable resources.

Beautiful lightning leading to a bright career

Maria knew early on that she wanted to become an engineer: During a two-week school internship in the high-voltage testing hall of the Technical University of Dresden, she discovered her love for electrical engineering. "I saw lightning and it crackled loudly. And I thought: such an electrical discharge looks simply beautiful,” Maria says laughing. “After the first few days of my internship, I just knew: That's what I want to do! That's what I want to study!"

That strong determination, which in the beginning was still smiled at by family and friends as a 15-year-old’s childish infatuation with an internship, turned out to be the starting point of a purposeful career: Further internships at the Technical University of Dresden followed while she was still at school, and directly after graduating Maria started her diploma studies in electrical engineering there and gained more experience abroad during a semester at the Saint Petersburg State Polytechnic University in Russia.

During a half-year internship in China, she received her first hands-on experience with the topic of high-voltage direct current (HVDC) transmission converters for the Ningdong-Shandong HVDC connection. The topic appealed to her because "the technology has so many advantages and I really had the feeling that I could still discover something there.”

And there was indeed more to discover: While the broad range of topics covered in her basic studies is especially beneficial today in her role as a senior engineer, Maria also knew she wanted to get more specific after reaching her diploma in the field of high-voltage technology and decided to pursue a PhD. The topic of her thesis: Flashover behavior of gas-solid insulating systems under DC voltage stress.

Direct current is patient

In the tests she conducted as part of her thesis, one central question was: At what voltage level and after which time does a breakdown or flashover occur, i.e. at what point does the insulating system in the switchgear become conductive, losing its insulating capabilities? By experimenting with various voltage stress durations, Maria observed the differences between the application of AC and DC voltage to the insulating system. And direct current is patient:

Only with long-term testing was Maria able to experimentally prove that the electrical field in DC GIS is changing: “Compared to AC GIS, the DC GIS gas-solid insulating system is exposed to an electrostatic field at the time of energization, followed by a field transition to an electric flow field that is strongly influenced by several factors, such as the materials used and their temperature.”

When, after finishing her PhD, Maria led the development of the DC GIS at Siemens Energy, these were important insights: While the DC GIS is based on the company's proven AC GIS technology, a new insulator needed to be developed and tested that could handle these DC-specific aspects. And with her extensive education and experience in high-voltage engineering from the university, she was also able to conduct several tests of the DC GIS and if needed also work hands-on with the equipment – sometimes to the surprise of her colleagues.

When Maria talks about the challenges that come with working in male-dominated areas, it goes from work clothes, with sizes primarily geared to men, to the fact that many colleagues first question a young female engineer’s abilities – resulting in the feeling of having to prove oneself over and over again. By confidently focusing on her own technical skills and challenging herself and others to keep developing them, Maria helps overcome gender stereotypes and is a role model for other young engineers, showing them just how exciting the field can be and increasing their likelihood of becoming innovators themselves.

Maria Kosse accompanied the development of the DC GIS for DolWin kappa from the very beginning. Now the system is being used offshore for the first time.

Stretching beyond technological limits

And now? Development never stands still: While the first generation of DC GIS was available for up to ±336 kilovolts (kV), today it is already available up to ±550 kV – an essential progression in technology to be able to realize even more powerful grid connections with up to two gigawatt power capacity in the future.

Not far from Cádiz, Hercules is said to have placed the Latin inscription Non plus ultra, in English "No further", at the exit of the Mediterranean Sea to mark the end of the world as we know it. Against the backdrop of climate change, the energy landscape is being completely rethought around the world and the boundaries of the known in technology need to be broken again and again – just like Maria and her team have done with the development of the DC GIS. While today Maria continues to work on the standardizations of the DC GIS technology within international technical organizations such as CIGRE and IEC, engineers at Siemens Energy are already working on the next generation of the DC GIS that uses climate-neutral Clean Air, an industrially purified air, instead of fluorinated gases to make the transport of wind energy even greener.

Because one thing is clear: If we don't manage to efficiently integrate renewables into our energy systems and thereby limit global climate change, then we really will come to mark the end of the world as we know it.

August, 2022

Christina Hümmer works in the communications department at Siemens Energy.

Combined picture and video credits: Siemens Energy; TenneT