UK G99 (Type A-C) ride-through requirements
Low-voltage ride-through, Frequency ride-through for the United Kingdom. Every breakpoint below is read from the code itself, and where a point was taken off a published figure rather than stated in the clause, the section under that chart says so — an envelope that stops where its published chart stops.
What is the low-voltage ride-through envelope for UK G99 (Type A-C)?
The plant must ride through for any voltage that stays on or above this envelope. The envelope holds 0.1 pu from t = 0 to 140 ms; then ramps linearly from 0.1 pu at 140 ms to 0.85 pu at 2.2 s; then 0.85 pu from 2.2 s, plotted to 3 min.
The clause states this boundary as a line; intermediate points are interpolated between its stated vertices. The envelope stops where the published chart stops; the code states no end time.
Applies to Type C-D power park modules connected below 110 kV (Table 13.5; includes ≥50 MW Type D)
| From | To | Voltage | Between the points |
|---|---|---|---|
| 0 | 140 ms | 0.1 pu | Held flat |
| 140 ms | 2.2 s | 0.1 → 0.85 pu | Ramps linearly |
| 2.2 s | plotted to 3 min | 0.85 pu | Held flat |
The clause this came from
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. The code defines a linear recovery ramp; the vertices are read from the clause and the chart draws the segment between them.
What is the frequency ride-through envelope for UK G99 (Type A-C)?
The plant must ride through between the upper and lower bands. The upper (over-frequency) band holds 52 Hz from t = 0 to 15 min; then 51.5 Hz from 15 min to 90 min; then 51 Hz from 90 min onward — the last band the envelope defines, with no stated end time. The lower (under-frequency) band holds 47 Hz from t = 0 to 20 s; then 47.5 Hz from 20 s to 90 min; then 49 Hz from 90 min onward — the last band the envelope defines, with no stated end time.
The last band has no stated end time. The clause below states a continuous region — highlighted; check which band it covers, because it is not always the last one.
Applies to Type A-C power park modules connected below 110 kV
Upper limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 15 min | 52 Hz | Held flat |
| 15 min | 90 min | 51.5 Hz | Held flat |
| 90 min | no stated end | 51 Hz | Held flat |
Lower limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 20 s | 47 Hz | Held flat |
| 20 s | 90 min | 47.5 Hz | Held flat |
| 90 min | no stated end | 49 Hz | Held flat |
The clause this came from
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'.
Who does UK G99 (Type A-C) bind, and since when?
Type C-D power park modules connected below 110 kV (Table 13.5; includes ≥50 MW Type D). No date of effect is published here — grid codes are reissued, so check the current issue before relying on it.
These figures are a reading aid, not legal advice. Grid codes are reissued: verify against the current edition before you design to them.
Digitised operating parameters beyond ride-through — droop, reactive capability, operating ranges — are published for 36 of the 66 codes in this atlas, not yet for UK G99 (Type A-C). That is a gap on this site, not a statement that UK G99 (Type A-C) sets none — the atlas hub marks the codes that carry them.
Curve data last checked against the code on — 66 standards, 130 envelopes, published by bess.engineer under CC BY 4.0.
Questions this page answers about UK G99 (Type A-C)
- Does UK G99 (Type A-C) require ride-through, or only that the plant does not trip?
- Ride-through. Every envelope on this page is a performance duty the plant must meet, not a protection-setting no-trip boundary — they are different obligations. That is what these curves are; they are not everything UK G99 (Type A-C) contains. The requirement sentence under each chart says which side of the curve is the compliant one.
- Are the numbers on this page taken from UK G99 (Type A-C) itself?
- Every breakpoint is read from the code, and where a point was taken off a published figure rather than stated in the clause, the section under that chart says so — on this page that includes an envelope that stops where its published chart stops. The clause each curve came from is quoted under it.
- Which events are charted for UK G99 (Type A-C)?
- UK G99 (Type A-C) is charted here with 2 envelopes — low-voltage ride-through, frequency ride-through (LVRT, FRT). No high-voltage envelope is charted here — check UK G99 (Type A-C) itself before concluding it sets none.
Ride-through, in context.
An envelope is a compliance boundary; understanding why it exists is a different question. The ride-through and grid-forming entries cover the engineering, and the Engineering Foundations course builds it from the physics up.
Also for the United Kingdom: UK G99 (Type D)
Elsewhere in Europe: Norway (Statnett NVF 2025), Poland (PSE Wymogi 2025), Romania (Transelectrica/ANRE storage norm), Spain (P.O. 12.3), Sweden (EIFS 2018:2), and 13 more