Even though the market creates a balance during the planning phase, the system is continuously exposed to factors that may disturb this balance, such as weather-related fluctuations in consumption, short-term changes in major industrial consumption, breakdowns in production facilities or power line outages or other grid component breakdowns. To be able to handle such unforeseen events, it is essential that there are sufficient reserves in the power system.
Momentary imbalances are initially regulated by primary regulation. If the imbalance continues for several minutes, secondary regulation will take over, thus freeing up primary regulation resources for regulation of new imbalances. Both primary and secondary reserves are activated automatically due to changes in the grid frequency. If further regulation is necessary, tertiary regulation (regulating power) will be activated which, correspondingly, will make secondary regulating resources available. Tertiary regulation is activated manually by the Nordic system operators. In Norway this is Statnett’s National Control Centre.
Primary, secondary and tertiary reserves are acquired through market solutions.