In Europe a grid frequency of 50 Hertz is used for the electrical power supply by AC voltage. In North America and Japan, and on railways and aircraft, different grid frequencies are used. The Hertz unit of frequency was named after the German physicist Heinrich Hertz.

To ensure the frequency remains at a stable level, the balance between production and consumption of electrical power must always be right. If there are deviations, this leads to a change in the grid frequency. If the frequency in the grid drops or rises, electrical devices and even generators can be damaged.

It is the responsibility of Swissgrid to detect grid overload or underload promptly. Very accurate measurements of the grid frequency are taken for this purpose. In the event of even minimal deviations in grid frequency from the setpoint value, action is taken to balance out the load in the grid.

For this to happen, certain power plant capacities need to be available at all times. In the event of a fault, neighbouring grids can help to stabilise the frequency of the overall grid by providing or drawing power at a higher rate.