California Rule 21 — ride-through requirements

The LVRT, HVRT, FRT envelopes a grid-scale battery must meet under California Rule 21 (US), 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; 1s → 0 pu; 1.001s → 0.5 pu; 10s → 0.5 pu; 10.001s → 0.7 pu; 20s → 0.7 pu; 20.001s → 0.88 pu verified
high-voltage ride-through (HVRT) ride-through 0.001s → 1.2 pu; 12s → 1.2 pu; 12.001s → 1.1 pu verified
frequency ride-through (FRT) ride-through High: 0.1s → 61.8 Hz; 299s → 61.8 Hz; 299.001s → 61.2 Hz | Low: 0.1s → 57 Hz; 299s → 57 Hz; 299.001s → 58.8 Hz verified

Where these values come from

  • LVRT PG&E Electric Rule 21, Sheet 193, Table Hh-1b 'Smart Inverter Voltage Ride-through Settings' (V>1.20 cease to energize; 1.10<V<=1.20 momentary cessation 12 s; 0.88<=V<=1.10 continuous; 0.70<=V<0.88 mandatory 20 s; 0.50<=V<0.70 mandatory 10 s; V<0.50 momentary cessation 1 s) and Table Hh-1a shall-trip settings (UV1 0.88 / 21.0 s; UV2 0.50 / 2.0 s), Advice 7692-E effective August 29, 2025, Corroborated by the legacy SDG&E Rule 21 Sheet 122 Table Hh-1 (Advice 2860-E, effective July 5, 2016): LV3 V<50% ride-through until 1 sec; LV2 50-70% until 10 sec; LV1 70-88% until 20 sec; NN 88-110% indefinite.
  • HVRT PG&E Electric Rule 21, Sheet 193, Table Hh-1b: '1.10 < V <= 1.20 | Momentary Cessation | 12 | 0.083' and 'V > 1.20 | Cease to Energize | NA | 0.16'; Table Hh-1a OV2 1.20 / 0.16 s, OV1 1.10 / 13.0 s. Advice 7692-E effective August 29, 2025, Corroborated by legacy SDG&E Rule 21 Sheet 122 Table Hh-1, HV1 110<V<120, 'Ride-Through Until 12 sec', Momentary Cessation, Maximum Trip Time 13 sec.
  • FRT PG&E Electric Rule 21, Sheet 196, Table Hh-2b 'Frequency Ride-Through Settings Table' (f>62.0 no RT; 61.2<f<=61.8 Mandatory Operation 299 s; 58.8<=f<=61.2 Continuous Infinite; 57.0<=f<58.8 Mandatory Operation 299 s; F<57.0 no RT), section Hh 'Smart Inverter Generating Facility Design and Operating Requirements for UL1741SB Inverters', Advice 7692-E effective August 29, 2025, Superseded values from SDG&E Rule 21 Sheet 124 Table Hh-2 (Advice 2860-E, effective July 5, 2016): f>62 no ride-through 0.16 s trip; 60.5<f<62 mandatory 299 s; 58.5<f<60.5 continuous; 57.0<f<58.5 mandatory 299 s; f<57.0 no ride-through 0.16 s trip. Cross-checked against IEEE 1547-2018 Table 18 shall-trip defaults (OF2 62.0/0.16 s, OF1 61.2/300 s, UF1 58.5/300 s, UF2 56.5/0.16 s) as reproduced in NERC Reliability Guideline 'BPS Reliability Perspectives on the Adoption of IEEE 1547-2018', March 2023, Table 1.3.

Last checked against the source document on .

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