NERC PRC-029-1 Compliance for Inverter-Based Resources

Q: Does PRC-029-1 require more than just staying connected during a disturbance?

Yes. PRC-029-1 also specifies how the facility must behave during and after a disturbance, including active power and reactive power response. A site that trips no protection but curtails output or injects reactive power incorrectly during a voltage event may still be out of compliance. Performance must be assessed alongside protection settings, which often requires coordination with the inverter manufacturer and review of the control mode configuration.

What Is PRC-029-1?

NERC PRC-029-1 is a mandatory reliability standard that requires inverter-based resources (IBRs) to remain connected to the grid during frequency and voltage disturbances, and to meet specific performance criteria while doing so.

Grid operators have long required generating facilities to ride through disturbances rather than disconnect at the first sign of trouble. With synchronous generators, the mechanical inertia of the machine provided some inherent stability during transient events. IBRs have no such inertia, and their control systems can react to disturbances in milliseconds. If protection settings are not carefully configured, a solar or wind facility can drop off the grid at exactly the moment the grid needs it most. PRC-029-1 sets the boundaries within which IBR protection may not operate.

Who Must Comply?

PRC-029-1 applies to Generator Owners (GOs) and Generator Operators (GOPs) of inverter-based resources in two categories:

BES IBRs

IBRs that qualify as Bulk Electric System (BES) elements under the NERC BES definition. This generally includes facilities with a nameplate rating of 75MVA or greater that interconnect at or above 100 kV. BES IBRs are subject to the full requirements of the standard.

Utility-scale solar photovoltaic (PV) facilities
Wind generation facilities using Type 3 and Type 4 turbines
Battery energy storage systems (BESS) connected via inverters

Category 2 IBRs (Aggregate Nameplate >20MVA and Interconnected at >60kV)

IBRs that fall below the BES threshold but are still subject to the standard based on their interconnection voltage and nameplate rating, as specified in the PRC-029-1 applicability table. Category 2 applicability reflects NERC's recognition that smaller IBRs connected at transmission voltage can still contribute to grid reliability events when they trip in large numbers.

Key Requirements Under PRC-029-1

PRC-029-1 defines "must Ride-through zones," rather than "no-trip zones" meaning frequency and voltage ranges within which IBRs must stay online. The standard also sets time-based ride-through requirements for conditions outside the continuous operating zone, and specifies how the facility must perform during and after a disturbance.

Frequency Ride-Through

IBRs must remain connected during over-frequency and under-frequency events within defined boundaries. The standard sets minimum duration requirements at varying frequency levels, so that IBRs do not trip during recoverable grid events. The standard also applies requirements to the facility's response to the event that must be studied for compliance.

Voltage Ride-Through

IBRs must withstand both over-voltage and under-voltage conditions for defined durations. Low-voltage ride-through (LVRT) and high-voltage ride-through (HVRT) requirements keep IBRs online through fault events that cause temporary voltage swings at the point of interconnection. The standard also applies requirements to the facility's response to the event that must be studied for compliance.

Protection Setting Verification

Generator Owners must verify that frequency and voltage protection settings on their inverters and plant-level controls do not operate within the PRC-029-1 ride-through boundaries and must studying the characteristics of the site's response. This typically requires reviewing inverter firmware, relay settings, and plant controller configurations.

Documentation and Evidence

Compliance requires documentation that is traceable to the applicable requirement, manufacturer data, and site-specific configuration. Generic or assumption-based evidence packages do not hold up under audit.

Common Compliance Challenges

PRC-029-1 is more involved than reading the ride-through curves and checking a box. A few issues come up repeatedly across IBR projects of all types and sizes:

Inverter-Level vs. Plant-Level Protection

Protection settings exist at multiple points in the collection system: individual inverters, medium-voltage equipment, and the plant controller. Each level must be evaluated separately. The key complication is that the voltage seen at the inverter terminals during a fault differs from the voltage at the point of interconnection, due to the voltage drop across the site-specific collector system impedance. Each study case produces a different voltage profile through the collection system, so evaluating inverter-level settings requires translating those voltages on a case-by-case basis using the actual collector impedance of that facility.

Performance Requirements, Not Just Ride-Through

PRC-029-1 does not simply require that an IBR stay connected. Assessments must also consider how the site behaves during and after a disturbance, including active power and reactive power response. A site that trips no protection but curtails output or injects reactive power incorrectly during a voltage event may still be out of compliance. Performance must be assessed alongside protection settings, which often requires coordination with the inverter manufacturer and review of the control mode configuration.

Firmware and Manufacturer Limitations

Some inverter models have firmware that limits how ride-through settings can be configured. What is and is not adjustable varies by manufacturer, model, and firmware version. When settings cannot be freely changed, the compliance path depends on accurately documenting the inverter's actual behavior and demonstrating whether that behavior meets the standard's boundaries.

Legacy Sites and Retrofit Projects

Facilities built before PRC-029-1 was effective may have settings that were acceptable under prior standards but no longer comply. Bringing these sites into compliance often requires coordination with the inverter manufacturer, the utility, and the regional entity, particularly when firmware updates or hardware modifications are involved. Facilities with exclusions must have auditable documentation listing the exclusion and level of the standard that the facility can comply with.

How Thomas Whitt Consulting Can Help

TWC performs PRC-029-1 compliance engineering for IBR owners and operators across North America. Our assessments are referenced, traceable, and built to hold up under regional entity audit.

Model and Data Collection Review

We review the models you have developed for the facility (if any) and the associated documentation for consideration in an assessment. If models are insufficient, we can offer to improve model representation, or work with the OEM to assess concerns not included in the model.

Compliance Assessment

We evaluate your existing frequency and voltage protection settings against the PRC-029-1 ride-through boundaries, translating settings through the collector system to a common voltage basis and identifying any gaps that require remediation.

Setting Recommendations

Where settings do not meet the standard, we develop technically grounded recommendations for adjustments, coordinated with your inverter manufacturer's capabilities and your interconnection agreement requirements.

Audit-Ready Documentation

We prepare evidence packages with requirement-by-requirement documentation, source data references, and plot simulation results. Each test is organized to address one or more of the standard's requirements as auditors review them.

NERC PRC-029-1: Frequency and Voltage Ride-Through Requirements for Inverter-Based Resources