Electricity is not stored in the wires. Every megawatt a kettle draws has to be
generated in the same instant, somewhere, by something. The frequency of the grid is
the reading on that balance, and you are holding it at 50.00 Hz.
1
Surplus raises the frequency, deficit lowers it. How fast it moves is set by the spinning mass online: df/dt = f₀·ΔP / (2·Ek). Fewer turbines turning means a twitchier grid.
2
Inertia comes from rotors. Thermal and hydro machines store kinetic energy in their shafts. Wind and solar inverters store none, unless you deliberately ask them to fake it.
3
Everything you order arrives late. A battery answers in under a second. Hydro in twelve. Combined-cycle gas takes ninety seconds to acknowledge and then moves 26 MW a minute. Nuclear barely moves at all.
4
Droop is automatic. Governors catch a deviation in seconds without asking you, but they settle off nominal. AGC walks it back over minutes. You handle everything bigger.
5
48.8 Hz sheds load. Under-frequency relays start disconnecting customers, five percent at a time. It is the grid saving itself, and it counts against you.
RoCoF = 50 × ΔP ÷ (2 × Ek) Hz/s
DRAG orbit the room 1–7 pick a unit Q W cycle units ← → target ±25 MW ↑ ↓ ±100 MW , . droop A AGC G grid-forming S shed load R restart M mute