Grid regulation

Primary control

The frequency of the power grid is directly linked to the speed of the electricity-producing synchronous generators in the grid, and is maintained at the same level throughout the grid. In most of the world , the target grid frequency is 50 Hz. Deviations from the target frequency occur when supply and demand are not in balance, and are only allowed to a very minimal extent. The primary control reserve – also known as the frequency containment reserve (FCR) – is used to stabilise grid frequency. It is activated by all TSOs across Europe in the synchronously interconnected system (solidarity principle). Thus if an imbalance occurs between production and consumption in the European interconnected system, for example when a power plant fails or when injections and withdrawals of electricity deviate from the forecasts, the grid frequency begins to deviate from the 50 Hz target. If no action is taken, the frequency deviation would keep increasing to the point of blackout after just a short period of time. To avoid this, all control area operators activate the primary control reserve to stabilise the grid frequency. This occurs automatically and nearly instantaneously within a matter of seconds. Simultaneously with the primary control reserve, the secondary control reserve – also known as the automatic frequency restoration reserve (aFRR) – is also activated in the control area in which the imbalance exists to relieve the burden on the primary reserve and restore its availability. This moreover restores the targeted grid frequency of 50 Hz.
The total primary control reserve maintained by the TSOs in the continental Europe interconnected system amounts to 3,000 MW. The System Operation guideline (SOGL) defines the volume of power reserves to be kept available by the individual TSOs based on their annual output.