Regulator
What the grid is actually held to — the limits from NESO's Frequency Risk & Control Report (FRCR) and the Security & Quality of Supply Standard (SQSS) — and, alongside each, the engineering basis TSGB argues should sit beside them.
Where the grid is right now
liveFrequency
Nominal 50.0 Hz. NESO holds a tight operational band in normal running; the statutory band is the licence obligation; below the LFDD line, load is automatically shed.
48.8
49.5
49.8
50.0
50.2
50.5
Rate of change of frequency (RoCoF)
How fast frequency falls after a loss — set by the largest loss divided by the system's inertia. The protection setting the grid was originally coordinated to has been progressively relaxed as inertia fell.
Largest infeed loss
The single biggest infeed the system secures against. The SQSS figures were sized in the thermal era; TSGB argues the credible loss is better read as the largest group that can trip on a common mode — a shared converter, landfall or route.
The live dial tracks the largest common-mode infeed at risk right now from the interconnector clusters and the largest single unit — see it move against these lines.
System inertia
The stored rotational energy that resists frequency change. The FRCR floor pairs the 1,800 MW secured loss with the 0.5 Hz/s RoCoF setting. TSGB argues for pairing a larger common-mode loss with the original 0.125 Hz/s coordination — which lifts the floor well above today's.
Purchased time
Seconds of ride-through before frequency reaches the 49.2 Hz working set-point after a large common-mode infeed loss, at each inertia level. The human-response standard is 3–5 s; TSGB adopts 4 s. Below the FRCR floor there is under a second.
GVA·s → seconds. Green = meets the 4-second floor; red = below the FRCR floor.
The events the standard is graded against
Standards: NESO's Frequency Risk & Control Report 2024 — the operative edition, as FRCR 2025 was not approved and FRCR 2026 suspended (see the FRCR timeline) — and the NETS Security & Quality of Supply Standard. TSGB-basis figures are TSGB analysis. Always verify against the primary documents for operational use.