The operators in the grid control room at Swissgrid are not just responsible for protecting the transmission grid from fluctuations but also for protecting it against high loads. Lines and transformers can transmit only a limited amount of energy.
To prevent a grid element from overloading, Swissgrid uses the n-1 rule, which means that if a grid element fails, all the other grid elements in the transmission grid must still have enough capacity to transmit the additional energy. Every 5 minutes, the automatic grid calculation simulates whether this rule is being upheld. If the n-1 rule is violated, lines or transformers are at risk of overloading, and the operators jump into action.
They can use switching operations to influence the load flows in the transmission grid, meaning they disconnect or connect lines in substations or adjust the flow of electricity through the transformers. This makes it possible to reduce the load on a certain line.
The operators in the Swissgrid grid control rooms also have the option of carrying out a redispatch. A redispatch instructs certain power plants to reduce their production and others to increase their feed-in. All in all, the same amount of energy is still fed into the grid; it is simply geographically redistributed to reduce the load on the line that is at risk.
As Swissgrid intervenes in power plant operation during redispatching, costs are incurred. In the event of national redispatching, i.e. if there is grid congestion in Switzerland and Swissgrid deploys Swiss power plants, these costs are incorporated into the charge for use of the grid.
Redispatching can also take place across national borders. In this case, Swissgrid works with the transmission system operators in neighbouring countries, who instruct the relevant power plants to adjust their production accordingly. Swissgrid pays the resulting costs out of the revenue from auctions to allocate cross-border line capacities. If a foreign transmission system operator requests support from Swiss power plants, the costs are borne by the transmission system operator.