IEEE 1547-2018 Cat III ride-through requirements
Low-voltage ride-through, High-voltage ride-through, Frequency ride-through for the United States. 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 — a table or figure read from an authorised reprint.
What is the low-voltage ride-through envelope for IEEE 1547-2018 Cat III?
The plant must not disconnect for any voltage that stays on or above this envelope. The envelope holds 0 pu from t = 0 to 1 s; then 0.5 pu from 1 s to 10 s; then 0.7 pu from 10 s to 20 s; then 0.88 pu from 20 s onward — the last band the envelope defines, with no stated end time.
The clause defines part of this envelope as a momentary-cessation region, where output ceases but the plant does not disconnect; elsewhere inside it the clause requires mandatory operation. Which region a point falls in is in the clause below, not in the curve. Read from an authorised reprint of the table rather than the standard itself, and cross-checked against the other codes cited below.
Applies to DER at the distribution PCC, Category III abnormal performance
| From | To | Voltage | Between the points |
|---|---|---|---|
| 0 | 1 s | 0 pu | Held flat |
| 1 s | 10 s | 0.5 pu | Held flat |
| 10 s | 20 s | 0.7 pu | Held flat |
| 20 s | no stated end | 0.88 pu | Held flat |
The clause this came from
IEEE 1547-2018 Table 16 / Figure H.4 ride-through capability regions, reproduced under IEEE copyright permission in EPRI's 'Crash Course: IEEE Std 1547-2018' (slide 47, 'Actual Abnormal Voltage Requirements for Category III'): momentary-cessation capability box 0.00–0.50 pu ending at 1 s; mandatory-operation capability 0.50–0.70 pu to 10 s and 0.70–0.88 pu to 20 s. Same regions in the MISO Guideline for IEEE Std 1547-2018 Implementation, Figure 4 (Category III), p.26. Independently confirmed in EPRI's reference implementation OpenDER (src/opender/operation_status/rt_crit.py, CAT_III branch): 0.7≤V<0.88 → pass at t>20 s; V<0.7 → t>10 s; V≤0.5 → t>1 s. Operating-mode bands also confirmed by the ISO-NE/Massachusetts TSRG 'Default IEEE 1547-2018 Setting Requirements' Table V (V<0.50 Momentary Cessation; 0.5≤V<0.88 Mandatory Operation; 'Identical' to 1547-2018 Cat III).
What is the high-voltage ride-through envelope for IEEE 1547-2018 Cat III?
The plant must not disconnect for any voltage that stays on or below this envelope. The envelope holds 1.2 pu from t = 0 to 12 s; then 1.1 pu from 12 s onward — the last band the envelope defines, with no stated end time.
The clause defines part of this envelope as a momentary-cessation region, where output ceases but the plant does not disconnect. Which region a point falls in is in the clause below, not in the curve. Read from an authorised reprint of the figure rather than the standard itself, and cross-checked against the other codes cited below.
Applies to DER at the distribution PCC, Category III abnormal performance
| From | To | Voltage | Between the points |
|---|---|---|---|
| 0 | 12 s | 1.2 pu | Held flat |
| 12 s | no stated end | 1.1 pu | Held flat |
The clause this came from
IEEE 1547-2018 Category III ride-through capability figure (IEEE copyright, adapted/reprinted with permission) in EPRI's 'Crash Course: IEEE Std 1547-2018', slide 47: the orange 'Momentary Cessation Capability' region spans 1.10–1.20 pu and terminates at 12 s. Same 12 s edge in MISO Guideline for IEEE Std 1547-2018 Implementation Figure 4 (Category III), p.26. Confirmed in EPRI OpenDER rt_crit.py: CAT_III high-voltage branch is a single test 'if 1.1 < v_high … if rt_time_hv <= 12: rt_pass_time_req = True' (12 s), whereas the CAT_I/CAT_II branches contain exactly the published 1.15→1 s / 1.175→0.5 s / 1.20→0.2 s ladder.
What is the frequency ride-through envelope for IEEE 1547-2018 Cat III?
The plant must ride through between the upper and lower bands. The upper (over-frequency) band holds 61.8 Hz from t = 0 to 299 s; then 61.2 Hz from 299 s onward — the last band the envelope defines, with no stated end time. The lower (under-frequency) band holds 57 Hz from t = 0 to 299 s; then 58.8 Hz from 299 s 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. Read from an authorised reprint of the table rather than the standard itself, and cross-checked against the other codes cited below.
Applies to DER at the distribution PCC, Category III abnormal performance
Upper limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 299 s | 61.8 Hz | Held flat |
| 299 s | no stated end | 61.2 Hz | Held flat |
Lower limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 299 s | 57 Hz | Held flat |
| 299 s | no stated end | 58.8 Hz | Held flat |
The clause this came from
IEEE 1547-2018 Table 19, reproduced verbatim in the ISO-NE / Massachusetts TSRG 'Default IEEE 1547-2018 Setting Requirements' Table II ('Frequency ride-through requirements for DER of abnormal operating performance-Category I, Category II, and Category III': f > 62.0 no ride-through; 61.2 < f ≤ 61.8 Mandatory Operation; 58.8 ≤ f ≤ 61.2 Continuous; 57.0 ≤ f < 58.8 Mandatory Operation; f < 57.0 no ride-through — each marked 'Identical' to 1547-2018). Duration confirmed by EPRI OpenDER rt_crit.py (299 s timers at 61.2–61.8 Hz and 57.0–58.8 Hz) and by the '299 s' annotation on the IEEE-copyright frequency figure in the EPRI 1547-2018 crash course (slide 48). Trip-side coordination: 1547-2018 defaults OF2 62.0 Hz/0.16 s, OF1 61.2 Hz/300 s, UF1 58.5 Hz/300 s, UF2 56.5 Hz/0.16 s (MISO Guideline Table 6).
Who does IEEE 1547-2018 Cat III bind, and since when?
DER at the distribution PCC, Category III abnormal performance. 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 IEEE 1547-2018 Cat III. That is a gap on this site, not a statement that IEEE 1547-2018 Cat III 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 IEEE 1547-2018 Cat III
- Does IEEE 1547-2018 Cat III require ride-through, or only that the plant does not trip?
- Ride-through, with one qualification. On its LVRT and HVRT envelopes the clause defines part of the region as momentary cessation, where output ceases but the plant does not disconnect; on its LVRT envelope the clause requires mandatory operation elsewhere inside the region. Which region a point falls in is in the clause quoted under those charts, not in the curve.
- Are the numbers on this page taken from IEEE 1547-2018 Cat III 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 a table or figure read from an authorised reprint. The clause each curve came from is quoted under it.
- Which events are charted for IEEE 1547-2018 Cat III?
- IEEE 1547-2018 Cat III is charted here with 3 envelopes — low-voltage ride-through, high-voltage ride-through, frequency ride-through (LVRT, HVRT, FRT).
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 States: ERCOT (NOG 2.9.1), IEEE 2800-2022, NERC PRC-024-4 (ERCOT), NERC PRC-024-4 (no-trip), NERC PRC-024-4 (Western), NERC PRC-029-1 (IBR), and 5 more