Frequency
The repeating rhythm of an alternating-current system.
The marked interval covers one complete cycle of the waveform. The sketch is not drawn to a time scale.
Frequency is the number of AC cycles per second, measured in hertz. Grid operators work to keep it near its nominal value as electricity supply and demand change.
Reading the rhythm of AC
One complete repetition of an AC waveform is a cycle. Hertz counts those cycles per second. A frequency of 50 Hz means 50 cycles each second; it does not describe how much power the system is delivering.
In a synchronous grid, frequency is closely tied to the balance between power supplied and power demanded, including network losses. When demand suddenly exceeds supply, frequency tends to fall. Controls and responsive resources act to arrest and correct the change.
Why it matters
Keeping frequency close to its nominal value helps connected equipment operate as intended and is a continuous task for system operators.