UK G99 (Type D) — ride-through requirements

The LVRT, FRT envelopes a grid-scale battery must meet under UK G99 (Type D) (UK), digitized breakpoint by breakpoint and checked against the clause it came from.

By Sergey Syrvachev — Director of Product Engineering, grid-scale BESS · 10+ GWh delivered

Part of: the grid-code ride-through chart — compare this against 63 other standards in 42 countries.

What this is, and is not. A reading aid compiled from the clause cited below — not a compliance document. The primary text governs. Every value here was read from a current primary source.

Breakpoints

Times are seconds from the start of the disturbance. Voltage is per-unit of nominal; frequency in hertz. An LVRT curve is a lower boundary (stay connected while voltage is on or above it), an HVRT curve an upper boundary, and FRT gives the band between its High and Low boundaries.

Event Duty Breakpoints Status
low-voltage ride-through (LVRT) ride-through 0.001s → 0 pu; 0.14s → 0 pu; 0.141s → 0.074 pu; 0.5s → 0.074 pu; 0.501s → 0.252 pu; 1s → 0.252 pu; 1.001s → 0.458 pu; 1.5s → 0.458 pu; 1.501s → 0.706 pu; 2.2s → 0.706 pu; 2.201s → 0.85 pu; 180s → 0.85 pu; 180.001s → 0.9 pu verified
frequency ride-through (FRT) ride-through High: 0.1s → 52 Hz; 900s → 52 Hz; 900.001s → 51.5 Hz; 5400s → 51.5 Hz; 5400s → 51 Hz | Low: 0.1s → 47 Hz; 20s → 47 Hz; 20.001s → 47.5 Hz; 5400s → 47.5 Hz; 5400s → 49 Hz verified

Where these values come from

  • LVRT ENA EREC G99 Issue 2, 10 March 2025, Table 13.6 and Figure 13.11 'Voltage against time curve applicable to Type D Power Park Modules connected at or above 110 kV': Uret 0, Uclear 0, Urec1 0, Urec2 0.85; tclear 0.14, trec1 0.14, trec2 0.14, trec3 2.2, figure axis to 180 s. Clause 13.3.1.1 makes the heavy black line of Figures 13.8-13.11 the ride-through boundary.
  • FRT ENA EREC G99 Issue 2 (2025), clause 13.2.1 (a)-(e) for Type C and Type D Power Generating Modules: 20 s at 47-47.5 Hz; 90 minutes at 47.5-49.0 Hz; continuous 49.0-51.0 Hz; 90 minutes at 51.0-51.5 Hz; 15 minutes at 51.5-52 Hz.

Last checked against the source document on .

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