NERC PRC-028-1: Disturbance Monitoring and Reporting Requirements for Inverter-Based Resources

IBR-specific monitoring equipment to capture the fast dynamics that conventional recorders miss

What Is PRC-028-1?

Inverter-based resources behave fundamentally differently from synchronous generators during grid disturbances. Where a synchronous machine responds to a voltage sag with mechanical inertia, an IBR can respond in milliseconds based on its control system settings, changing active and reactive power output at speeds that traditional disturbance recording equipment wasn't designed to capture.

After a series of significant IBR-related reliability events, NERC found that post-event investigations were repeatedly hampered by insufficient recorded data: events that happened at timescales conventional fault recorders couldn't resolve. PRC-028-1 was developed specifically to address this gap, establishing monitoring equipment requirements that can capture IBR dynamics at the speeds relevant to their control system behavior.

The standard runs parallel to PRC-002-5 but imposes IBR-specific requirements that go beyond what PRC-002-5 requires of conventional generators.

Who Must Comply?

PRC-028-1 applies to Generator Owners (GO) of inverter-based resources that meet the BES applicability criteria as well as Category 2 facilities with aggregate facility nameplates of >20MVA and interconnecting at >60kV. This generally includes:

Utility-scale solar PV, BESS, or Type 3/4 Wind facilities with a nameplate rating of 20 MVA or greater at or above 100 kV
Hybrid facilities that meet the applicable thresholds

Facilities below the BES threshold may still be designated for compliance by the regional entity based on reliability needs. The applicability determination should be confirmed with the regional entity for any facility near the BES boundary.

Key Requirements

IBR-Appropriate Monitoring Equipment

Install and maintain monitoring equipment capable of capturing IBR dynamics at the sampling rates and recording length required by the standard. Equipment must record at multiple points in the facility, including at or near the point of interconnection and at the feeder breakers. Like PRC-002, PRC-028 requires sequence of events recording, fault recording, and dynamic disturbance recording.

Triggering Configuration

Equipment must be configured with triggering conditions designed to capture IBR-relevant events, including voltage disturbances, frequency excursions, and unexpected real or reactive power changes. Trigger thresholds must be set to capture events without generating excessive noise recordings.

Data Retention

Recorded disturbance data must be retrievable for 20 days and must be provided within 15 days of a request. The retention obligation is operationally important, not just a compliance checkbox.

Documented Process and Commissioning Records

Upon request, Generator Owners should have documented processes for retrieving data as well as documentation of the commissioning and testing done on the recording system to ensure its compliance with the standard.

Common Compliance Challenges

Existing Equipment That Doesn't Meet IBR Requirements

Many IBR facilities were built with monitoring that doesn't meet the PRC-028-1 requirements for sampling rate, recorded data channels, or measurement point location. Facilities that transitioned from PRC-028 scope haven't always assessed whether their equipment meets the new standard.

IBR Requirements and OEM Involvement

The inverters themselves are required to report ride-through status as well as all fault codes and alarms. This requires coordination with the OEM to confirm and sometimes response times are slow.

Newer Standard with Evolving Audit Expectations

PRC-028-1 is relatively new, and audit expectations for evidence (particularly around equipment qualification and data channel requirements) continue to develop as regional entities gain experience with the standard. What constitutes adequate compliance documentation is still being established through audit findings and guidance.

Data Volume and Management

High-resolution IBR monitoring equipment generates substantially more data than conventional fault recorders. Facilities need to have a data management plan that considers storage, retrieval, and the reporting workflow. Owners should assess the storage capacity of their recording devices. Many IBR operators haven't formally addressed any of these.

How TWC Can Help

TWC supports IBR owners with PRC-028-1 compliance, from equipment gap assessments through reporting process development and evidence package preparation.

Applicability and Equipment Gap Assessment

We confirm the facility's PRC-028-1 applicability and evaluate existing monitoring equipment against the standard's technical requirements, identifying gaps to close if needed.

Equipment Specification

If equipment upgrades are needed, we define the technical requirements for IBR-appropriate monitoring equipment and work with vendors to confirm that proposed solutions meet the standard's criteria before purchase.

Equipment Configuration and Configuration

We assist with trigger threshold, sampling rate, and recording size settings selection based on site-specific IBR operating characteristics and support commissioning tests to confirm that the equipment captures representative events under actual site conditions.

Reporting Documentation

We provide compliance documentation covering equipment records, trigger configuration, and the data retention settings as well as commissioning tests showing recording per the standard.

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