PRC-029-2

R1 · Ride through voltage excursions

What it means. Each inverter-based resource must Ride-through, meaning stay connected and keep operating, anywhere inside the must ride-through zone of Attachment 1, including no trip on phase-locked-loop loss of synchronism. The standard lists the exceptions: disconnecting to clear a fault, a hardware limitation accepted under R4, a positive-sequence phase-angle jump of more than 25 electrical degrees from a non-fault switching event, and Volts per Hz at the high side of the main power transformer above 1.1 per unit for longer than 45 seconds or above 1.18 per unit for longer than 2 seconds.

Evidence an auditor expects. For design: dated inverter and plant protection setting sheets compared with the Attachment 1 voltage-time boundaries, engineering, procurement and construction (EPC) design documentation and dynamic simulation studies. For operation: sequence of events, fault and dynamic disturbance records for each voltage excursion, and, where the phase-jump exception is used, written confirmation from the Transmission Planner (TP), Reliability Coordinator (RC), Planning Coordinator (PC) or Transmission Operator (TOP) that a non-fault switching event occurred.

R2 · Deliver the right current during a voltage excursion

What it means. While voltage at the high side of the main power transformer stays in the continuous operation region, each inverter-based resource keeps delivering the lesser of its pre-disturbance or available real power (except during a frequency excursion), keeps delivering reactive power up to its limit and per its controller settings, and, below 0.95 per unit, follows its configured real or reactive power priority when it cannot deliver both. In the mandatory operation region it exchanges current up to its maximum capability on the affected phases, for both balanced and unbalanced disturbances, with reactive power priority by default unless its TP, PC, RC or TOP requires real power priority. In the permissive operation region it may enter current blocking only if needed to avoid tripping, and must restart current exchange within five cycles after positive-sequence voltage returns to the continuous or mandatory operation region. It must not itself push voltage above the high-voltage limits on recovery, and, once voltage returns to the continuous operation region, it restores real power to the lesser of its pre-disturbance or available level within 1.0 second, unless its TP, PC, RC or TOP sets a different level or time.

Evidence an auditor expects. Controller settings for real and reactive power priority, current injection and current blocking, original equipment manufacturer (OEM) capability documentation, and simulation results or event records showing the response.

R3 · Ride through frequency excursions

What it means. Each inverter-based resource must Ride-through, staying connected and operating, while frequency at the high side of the main power transformer stays inside the Attachment 2 must ride-through zone and the absolute rate of change of frequency is 5 Hz per second or less, unless an R4 hardware limitation applies. RoCoF (rate of change of frequency) is the average rate of change of calculated system frequency over 0.1 second or longer, and is not calculated during fault occurrence and clearance.

Evidence an auditor expects. Dated frequency and RoCoF protection setting sheets compared with Attachment 2 and the calculations behind them, plus disturbance monitoring records showing the plant's actual response to each frequency excursion.

R4 · Document hardware limitations

What it means. R4 applies to a Generator Owner whose inverter-based resource has known hardware limitations that prevent it from meeting Ride-through criteria in R1 to R3 and requires an exemption from specific Ride-through criteria, and that either is in service by the effective date of PRC-029-1 (October 1, 2026 in the United States), or is in service after that date and has both an interconnection agreement executed by that date and an equipment procurement contract for the hardware causing the limitation executed before September 1, 2025 (the United States date). The Generator Owner documents: identifying information of the resource (facility name and the Generator Owner's NERC Compliance Registry (NCR) number); which aspects of the Ride-through requirements the resource would be unable to meet and the capability of the hardware due to the limitation; and technical documentation verifying the limitation is due to hardware that would need to be physically replaced to meet all Ride-through criteria, and that it cannot be remedied by software updates or setting changes. It provides a copy to its Planning Coordinators, Transmission Planners, Transmission Operators, Reliability Coordinators and the Compliance Enforcement Authority (CEA); material the equipment manufacturer considers proprietary goes only to the CEA. The submission deadlines are set in the implementation plan (see the key dates above). It answers requests for more information within 90 days, gives the PC, TP, TOP and RC a copy of the CEA's acceptance within 90 days of receiving it, and, if it later replaces the hardware causing an accepted limitation, documents and communicates the change to the PC, TP, TOP and RC within 90 days. The exemption for that criterion then no longer applies. The hardware causing the limitation is understood as an integrated system of components: a combination in which replacing any subset of components would not remove the documented limitation.

Evidence an auditor expects. Technical evidence such as equipment vendor documentation of the hardware limitation, written engineering analysis, test results, or operational data supported by an engineering analysis; evidence of the submission to the CEA; for a resource in service after October 1, 2026, the fully executed interconnection agreement and procurement contract that establish eligibility; and dated transmittals to each recipient with their requests and responses.