The Swiss transmission grid is approaching its capacity limits. More than two-thirds of the Swiss transmission grid is over 40 years old and can no longer cope with the future requirements of increasing electricity consumption as well as the fluctuating feed-in from renewable energy. Even today, power plant operators have to reduce electricity production from hydropower because Swissgrid doesn't have sufficient grid capacity to discharge the energy. The Swissgrid Control grid control room is faced with major challenges in the operation of the Swiss transmission grid due to structural bottlenecks.
Unplanned grid loads can occur in the Swiss transmission grid at any time due to unforeseen events such as outages of grid elements (lines or transformers). The electricity tries to find its way through grid elements that are still intact, for example after the outage of a line. This unplanned electricity flow can lead to an overload of other grid elements.
At least every five minutes, Swissgrid Control determines the (n-1) load of the grid elements in the entire Swiss transmission grid based on thousands of current and voltage measurements. In the process, the load values that result for the remaining grid elements are calculated after the simulated outage of any element. The simulation shows which element of the entire still intact transmission grid would be loaded the most in case of the failure of another grid element. An (n-1) load that is greater than 100% means that this could lead to an overload and to the loss of another grid element if the overload remains. Therefore, the objective of grid operations is to keep the (n-1) load of the grid elements at a maximum of 100 per cent at all times.
The (n-1) simulation therefore does not represent the actual load in the transmission grid. However, the result of the simulation is used by Swissgrid Control for the preparation and execution of measures if the possibility of overrunning the (n-1) limits exist.