NOGRR 255

NOGRR 255

ERCOT Disturbance Monitoring Requirements for Inverter-Based Resources (Nodal Operating Guide Section 6.1.4)

Nodal Operating Guide Revision Request (NOGRR) 255 added Section 6.1.4 to the ERCOT Nodal Operating Guide: fault recording, sequence of events recording and phasor measurement units at inverter-based plants, with tighter time synchronization and faster data delivery to ERCOT than NERC PRC-028-1. Section 6.1.5, the Guide's maintenance and testing section, covers the Section 6.1.4 equipment by its own terms, so it is listed below as well. NOGRR 279 later removed the 50 percent interim milestone, leaving August 1, 2028 for existing resources and commissioning-based dates for newer ones.

Who it applies to

Transmission-connected inverter-based resource facilities in ERCOT at 60 kV with a gross aggregated nameplate capacity of 20 MVA at a single site, which GridStrong reads as 60 kV or above and 20 MVA or more: solar, wind and battery storage.
Energy storage resources should also check Sections 6.1.2 and 6.1.3 of the Nodal Operating Guide, which apply to all energy storage resources (ESRs).
Plants that also fall under NERC PRC-028-1 must meet both sets of requirements. Neither rule says which governs; designing to the stricter value on each point is usually the simplest way to meet both.

Key dates

August 1, 2024: NOGRR 255 effective (approved by the Public Utility Commission of Texas, PUCT, on July 25, 2024).
February 1, 2026: NOGRR 279 effective (PUCT approved January 15, 2026), replacing the 50 percent interim deadline with a single schedule.
August 1, 2028: equipment installed and configured at resources commissioned before July 25, 2024.
Within 365 days of commissioning: resources with a Standard Generation Interconnection Agreement (SGIA) signed on or before July 25, 2024 and commissioned after that date.
By commissioning: resources with an SGIA signed after July 25, 2024.

What each requirement asks for, in plain English.

6.1.4.1 · Time synchronization

What it means. Every sequence of events recording (SER), fault recording (FR) and phasor measurement unit (PMU) device is synchronized to a Global Positioning System (GPS) clock, or an ERCOT-approved alternative, within 100 microseconds of Coordinated Universal Time (UTC). That is ten times tighter than the PRC-028-1 limit for station devices.

Evidence ERCOT expects. Clock status or time-quality indication for each device.

6.1.4.1.1 · Sequence of events recording

What it means. Record the open and closed position of the breakers on the main power transformer, collector buses, and shunt static and dynamic reactive devices. Export in the ERCOT comma-separated values (CSV) layout (date, time, local time code, substation, device, state) with file names that follow the IEEE C37.232 (COMNAME) convention.

Evidence ERCOT expects. Device settings, the single line diagram mapping each breaker to its recording device, and sample exports.

6.1.4.1.2 · Fault recording

What it means. Record at the high side of the main power transformer, at least one generator-interconnected bus and any dynamic reactive device, either continuously or on triggers that include residual overcurrent of 0.20 per unit or less of rated current transformer (CT) secondary current, phase undervoltage between 0.85 and 0.90 per unit (or phase overcurrent or relay trip), phase overvoltage above 1.10 per unit, frequency below 59.5 Hz or above 60.5 Hz, and df/dt of -0.08125 or +0.125 Hz per second. Equipment installed on or replaced after June 1, 2024 records at 64 samples per cycle or more; equipment installed before then at 16 or more. Each record has at least two cycles before the trigger and at least 2 seconds in total, provided in the IEEE C37.111 (COMTRADE) format.

Evidence ERCOT expects. Trigger settings, device specifications with install dates, and sample records.

6.1.4.3 · Phasor measurement units

What it means. PMUs at the main power transformer and at least one generator-interconnected bus stream continuous IEEE C37.118.1 synchrophasor data at 60 samples per second or more from inputs sampled at 960 per second or more, to an ERCOT phasor data concentrator or to local storage.

Evidence ERCOT expects. PMU configuration, the communication link or storage design, and sample data.

6.1.4.4 · Retention and delivery

What it means. Keep all data for a rolling 20 calendar days, and keep event data used for model validation or provided for an event review for at least three years. Deliver requested data to ERCOT within seven calendar days of the request, against 15 under PRC-028-1.

Evidence ERCOT expects. Retention configuration, the event archive, and dated transmittals to ERCOT.

6.1.5 · Maintenance and failures

What it means. Calibrate or configure each device at installation, check data availability at least every 60 days or monitor it automatically, and restore failed recording within 90 calendar days or give ERCOT a restoration plan and timeline.

Evidence ERCOT expects. Maintenance work orders, verification records, and dated restoration plans sent to ERCOT.