NERC PRC-024-4 (Western) no-trip limits
Frequency no-trip boundary for the United States. Every breakpoint below is read from the code itself, and carries the clause it came from — so you can check it, not just cite it. This is a protection-setting no-trip boundary, not a ride-through performance duty — they are different obligations.
What is the frequency no-trip boundary for NERC PRC-024-4 (Western)?
The plant must not trip between the upper and lower bands. The upper (over-frequency) band holds 61.7 Hz from t = 0 to 30 s; then 61.6 Hz from 30 s to 3 min; then 60.6 Hz from 3 min onward — the last band the envelope defines, with no stated end time. The lower (under-frequency) band holds 57 Hz from t = 0 to 750 ms; then 57.3 Hz from 750 ms to 7.5 s; then 57.8 Hz from 7.5 s to 30 s; then 58.4 Hz from 30 s to 3 min; then 59.4 Hz from 3 min onward — the last band the envelope defines, with no stated end time.
A no-trip boundary: protection must not operate inside this envelope. Every breakpoint is stated in the clause cited below.
Applies to BES generator relay set points, Western Interconnection
Upper limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 30 s | 61.7 Hz | Held flat |
| 30 s | 3 min | 61.6 Hz | Held flat |
| 3 min | no stated end | 60.6 Hz | Held flat |
Lower limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 750 ms | 57 Hz | Held flat |
| 750 ms | 7.5 s | 57.3 Hz | Held flat |
| 7.5 s | 30 s | 57.8 Hz | Held flat |
| 30 s | 3 min | 58.4 Hz | Held flat |
| 3 min | no stated end | 59.4 Hz | Held flat |
The clause this came from
NERC PRC-024-4, Attachment 1 '(Frequency No Trip Boundaries by Interconnection)', Table 2 'Frequency Boundary Data Points – Western Interconnection' and Figure 2 (p.13); identical to PRC-024-3 Table 2.
Who does NERC PRC-024-4 (Western) bind, and since when?
BES generator relay set points, Western Interconnection. 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 NERC PRC-024-4 (Western). That is a gap on this site, not a statement that NERC PRC-024-4 (Western) 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 NERC PRC-024-4 (Western)
- Does NERC PRC-024-4 (Western) require ride-through, or only that the plant does not trip?
- This is a protection-setting no-trip boundary, not a ride-through performance duty — they are different obligations. Protection must not operate inside the envelope plotted on this page.
- Are the numbers on this page taken from NERC PRC-024-4 (Western) itself?
- Yes. Every breakpoint is read from the code, and each envelope carries the clause it came from, quoted in full under its chart — so you can check the figure against the standard rather than cite it from this page.
- Which events are charted for NERC PRC-024-4 (Western)?
- NERC PRC-024-4 (Western) is charted here with 1 envelope — frequency no-trip boundary (FRT). No low-voltage or high-voltage envelope is charted here — check NERC PRC-024-4 (Western) itself before concluding it sets none.
No-trip limits, 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: NERC PRC-024-4 (ERCOT), NERC PRC-024-4 (no-trip), NERC PRC-029-1 (IBR), NERC PRC-029-1 (Table 1: AC-connected wind IBR), Transient overvoltage (IEEE 2800 TOV), California Rule 21, and 5 more