Mains frequency

In a power grid with alternating voltage(alternating current), there is always a frequency that determines how fast the voltage "oscillates". In fact, these oscillations - like a loudspeaker - are sometimes audible, for example in the immediate vicinity of a transformer station (see transformer substation).
In the European electricity grid and many other energy supply grids around the world, a frequency of 50 hertz (frequency unit; Hz for short) is used. In North America, a grid frequency of 60 Hz is used. Fluctuations occur as soon as there is a strong imbalance between supplied and demanded energy in the power grid. If demand is higher than consumption, the frequency rises. Conversely, it falls. In general, problems arise quickly when there are strong fluctuations, which is why supply and demand must always be balanced. This works, for example, by power plants throttling or increasing their output.