UK G99 (Type A-C) — ride-through requirements

The LVRT, FRT envelopes a grid-scale battery must meet under UK G99 (Type A-C) (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 → 0.1 pu; 0.14s → 0.1 pu; 0.141s → 0.166 pu; 0.5s → 0.166 pu; 0.501s → 0.322 pu; 1s → 0.322 pu; 1.001s → 0.504 pu; 1.5s → 0.504 pu; 1.501s → 0.723 pu; 2.2s → 0.723 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 13.5 and Figure 13.10 'Voltage against time curve applicable to Type C and Type D Power Park Modules connected below 110 kV': Uret 0.1, Uclear 0.10, Urec1 0.10, Urec2 0.85; tclear 0.14, trec1 0.14, trec2 0.14, trec3 2.2 (figure axis extends to 180 s). Identical to Table 12.2 / Figure 12.6 for Type B PPMs. Type A: clause 11.3.1.
  • FRT ENA EREC G99 Issue 2 (2025), clause 13.2.1 (and identically 11.2.1, 12.2.1): '(a) 47 Hz - 47.5 Hz Operation for a period of at least 20 s'; '(b) 47.5 Hz - 49.0 Hz ... at least 90 minutes'; '(c) 49.0 Hz - 51.0 Hz Continuous operation'; '(d) 51.0 Hz - 51.5 Hz ... at least 90 minutes'; '(e) 51.5 Hz - 52 Hz ... at least 15 minutes'.

Last checked against the source document on .

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