Every AC power grid runs at a target frequency — 50Hz in the UK and most of the world. That frequency is not fixed by decree: it is a live signal produced by thousands of spinning generator turbines, all rotating in lockstep. When electricity demand (load) and supply (generation) match exactly, the turbines spin at exactly the right speed and frequency sits at 50Hz. The instant they diverge, the shared rotating mass of the grid speeds up or slows down, and frequency drifts with it.
Grid operators watch frequency to the hundredth of a hertz. In Great Britain, National Grid ESO must hold frequency within 50 ± 0.2Hz under normal conditions — a deviation of just 1% would already be considered a major system event.
A 3D power-grid diagram where city load and generator dispatch are pulled out of balance, showing the shared grid frequency drift away from 50Hz and automatic frequency-response controllers step in to pull it back.
Grid frequency reflects the real-time balance of supply and demand across every spinning generator on the network. Imbalance accelerates or decelerates that shared rotational speed, and grid inertia determines how fast frequency can drift (RoCoF).
Move the load and generation sliders apart to create an imbalance, choose a grid inertia level, and toggle automatic frequency response on or off. Try the "Trip a generator" button to see a sudden loss event and watch the controller respond.
Great Britain's National Grid ESO is contractually required to hold frequency within 50 ± 0.2Hz during normal operation — a deviation most people would never notice, but one that operators track to the hundredth of a hertz around the clock.