Why are power grids interconnected

Structure of the German electricity grid

Our power grid has four voltage levels that are operated with alternating current and are connected to one another by transformers.

The High voltage level works with 220,000 volts and 380,000 volts and, according to the Federal Ministry of Economics, had a length of around 35,000 kilometers in Germany in 2016. It forms the connection to the European networks and serves to connect the metropolitan areas over great distances with large long-distance lines and to supply very large industrial companies. Your lines are the highways of the German power grid.

The large power plants are connected to this level. The energy is sent through substations to the High voltage level passed, which operates with voltages of 60,000 to 220,000 volts and has a length of about 77,000 kilometers. It serves the supraregional distribution of electricity and supplies local electricity suppliers as well as large industrial plants, larger commercial enterprises and the railways.

The next level that Medium voltage level, works at 6,000 to 60,000 volts, has a length of around 479,000 kilometers and supplies, among other things, regional distribution networks as well as small and medium-sized companies in industry and commerce such as hospitals.

The Low voltage level finally supplies the electricity with the known voltage of 230 volts or 400 volts to end consumers such as households, small commercial companies and farms. The length of this network was 1.23 million kilometers.

In 2016, the entire power grid was around 1.8 million kilometers long and required 550,000 transformers to supply the various voltage levels. Around 1.45 million kilometers of this network, or almost 81 percent, were underground cables in 2015. Since it is practically impossible to store electricity, as much energy as is required has to be fed into this network every second, which means an enormous amount of control capacity to keep the network stable. The network frequency of 50 Hertz is particularly critical here, as it reacts very sensitively to fluctuations in the network, which in turn has far-reaching negative effects. Therefore, the grid frequency also serves as an indicator for controlling the stability of the power grid. This applies not only to the German network, but also to the entire European network because of the link with other countries.

Construction of the power grid