AC networks in Europe have a nominal frequency of 50 Hz. The responsible transmission system operators (TSOs) must guarantee this normal frequency within a narrow bandwidth at all times. Frequency stability is ensured by balancing power generation and consumption. If there are deviations between generation and consumption, a frequency drift occurs and the grid frequency changes. By providing primary control power (PRL), this frequency drift is stopped and the grid frequency is thus stabilized. The PRL must be fully activatable within 30 seconds and available for at least 15 minutes.
In Germany, there are four transmission system operators, each of which ensures a balance between electricity feed-in and withdrawal and the provision of balancing energy in their grid areas and cooperates in the grid control network. The costs for this are refinanced via the network charges. This association was extended to include Denmark, Belgium, the Netherlands, Switzerland, France and Austria.