Kriegers Flak CGS ‘Black Starts’ Rostock Power Plant

50Hertz and Energinet, together with the coal-fired power plant Rostock have performed a live simulation of a restart of the power grid after a power outage in Continental Europe with voltage supplied from Denmark through Kriegers Flak Combined Grid Solution (CGS).

According to 50Hertz, a land and sea cable connection between two countries and offshore wind power were used in real conditions for the first time to restart a power plant.

Kriegers Flak was utilised to fire up the power plant’s turbines, and to do this the Rostock power plant was first completely separated from the German power grid. Energinet provided the required 380-kV voltage via the CGS and the newly constructed converter systems in the substation in Bentwisch near Rostock.

“Several technical innovations were implemented in the Combined Grid Solution project. The back-to-back converter in the Bentwisch substation plays a key role here, as it synchronises and connects the two asynchronous power systems of Denmark and Germany. The successful start-up attempt was, therefore, also a practical test for this highly complex converter”, said Dr Frank Golletz, Chief Technical Officer at 50Hertz.

Start-up simulations are part of grid restoration plans, as their capability has to be tested regularly in their corresponding grid areas to guarantee the fastest possible restoration of the electricity grid after a power outage, according to 50Hertz, which added that this is usually involving storage or gas-fired power stations, because they do not need external power sources to start up. Other thermal power stations are usually not ‘black start capable’ without a powerful external power source, as they already need a lot of energy to start up, 50Hertz explained.

The interconnector between Germany and Denmark was officially inaugurated this October after the inauguration was delayed a couple of times due to the impact of COVID-19 restrictions.

The CGS has two offshore wind farms integrated in it, Baltic 1 and Baltic 2, which supply electricity to the 50Hertz transmission system. The Danish Kriegers Flak offshore wind farm will be connected to the CGS and the Danish transmission system next year.