Nant de Drance – Interview With Mr. Jürgen Wendorff, ABB

An exclusive insight into a The TRANSFORMER PROTECTOR installation
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About NDD

NANT DE DRANCE (NDD), the European flagship of the Hydro Power Plant industry, equips its 6 Generator Transformers with the SERGI TRANSFORMER PROTECTOR (TP) in Switzerland.


More than 400 workers, around 10 years of underground construction work in high mountains,17 km of tunnels and 1.7 million m³ of excavated rock. The Nant de Drance construction site is gigantic.

The result is one of the most powerful Pumped Storage Hydro Power Plant (PS HPP) plants in Europe. With an installed capacity of 900 MW, it will generate around 2.5 billion kWh of electricity per year after commercial operation in 2019.

We were able to interview Mr. Florian Brantschen, Electrotechnical Manager of the whole NDD Hydro Power Plant and Mr. Jürgen Wendorff, Project Manager at ABB AG – Transformatoren.

Please describe your position and your company?

I am a Project Manager at ABB AG – Transformatoren in Bad Honnef, Germany

How did you know about SERGI?

The SERGI TP was required in the specification of NDD.

Can you tell us more about this very specific project?

Nant de Drance is a large pumped storage power plant in the Wallieser Mountains. Pumped Storage Hydro Power Plants (PS HPP) essentially consist of an upper and a lower lake. In times of low electricity demand, water is pumped into the upper lake to flow down in times of high electricity demand and to be used by means of a generator to produce electricity. At the heart of the system are machines that are capable of pumping water into the upper lake and generating electricity by turbine in generator mode.

The flow for the operation of the machines, 6 at NDD, is transformed via transformers to the required voltage, from 400 kV mains voltage to 15.75 kV in pump operation and from 15.75 kV to 400 kV in generator operation. ABB manufactured, tested, transported to Switzerland, installed and commissioned these transformers, also 6 units, at the Bad Honnef plant in Germany. Commissioning is still in progress.

Since the transformers are installed in caverns in the mountain, the customer demanded the SERGI TP to minimize the risk of a transformer explosion in the event of a short circuit.

Can you give us the key steps for this project?

For the construction, testing, transport, installation and commissioning of 6 transformers, ABB received the order from NDD because we were able to meet the critical dimensions for road transport (maximum weight, due to a bridge on the way to the power plant) and external dimensions (for transport to the cavern). The competitors could not manage this.

Can you please explain the collaboration between ABB and SERGI?

The parts of the SERGI TP had to be integrated in the construction of the transformers. The engineers from ABB and SERGI were in close contact. The 3D CAD system created a 3D model with all the necessary parts of the SERGI TP. The customer was involved in this process, in order to consider the power plant requirements during installation and piping. Factory tests at ABB in Germany and SERGI in France ensured that the SERGI TP was built according to the specifications and performing well.

What were the technical challenges and how could they be solved?

In addition to the requirements already mentioned, the accurate fit of the systems must also be emphasized. As planned on paper, all system components could be assembled without major modifications.

The start of the project was already in 2009 and it will certainly take another year until this complex system will go into regular operation.