Ancillary servicesFrequency stability
The frequency of the European interconnected power system should be at 50 Hz. If, however, the load behaviour or the feed-in power changes, this can change the frequency. This is prevented by ensuring the frequency stability. The transmission system operators therefore maintain a certain amount of balancing power that can be switched on or off as required. Large generators have the advantage that they are somewhat inert and can therefore maintain the frequency for several seconds. During this time additional measures must be taken if necessary to keep the frequency stable. Balancing power can be divided into primary, secondary and minute reserve power.