Odessa Disturbance - nerc.com

1 RELIABILITY | RESILIENCE | SECURITY nerc | Report Title | Report Date I Odessa Disturbance Texas Events: May 9, 2021 and June 26, 2021 Joint nerc and Texas RE Staff Report September 2021 nerc | Odessa Disturbance Report | September 2021 ii Table of Contents Preface .. iv Executive Summary ..v Description of Disturbance ..v Key Findings and Recommendations .. vi Introduction .. 1 Background .. 1 Description of Analysis 1 Predisturbance Operating Conditions .. 2 Fault 3 Location of Disturbance and Affected Facilities.

2 4 Chapter 1: Detailed Findings from Disturbance Analysis .. 7 Gaps in Plant Performance Analysis and Performance Requirements .. 9 Improved Monitoring Data yet Still Challenges to Identify Root Causes ..10 PLL Loss of Synchronism Tripping Continues ..11 Protection Disabling ..12 Momentary Cessation and Plant-Level Control Interactions Persist ..13 Inverter Controls Leading to Facility Tripping ..14 Inverter Transient AC Overvoltage Tripping Persists ..15 Settings for Protection Set on or Near Curve ..16 PFR Controls Interactions and Abnormalities.

3 17 Reactive Power Injection While Inverters Gate Block ..19 Modifications to Default Time to Restart Upon Updates Needed to Misoperation Analysis ..20 Chapter 2: Modeling and Studies Asse ssment ..22 Model Limitations and Updates to Modeling ERCOT Model Type Review ..23 ERCOT Model Quality and Validation Process ..24 EMT Model Quality Requirements Improvements ..25 ERCOT Model Quality Check for May 9 ERCOT Interconnection Study Process Assessment ..26 ERCOT Interconnection Study Process Improvements ..26 System Model Validation Needed ..27 Relation to ERCOT Operations Table of Contents nerc | Odessa Disturbance Report | September 2021 iii Chapter 3: Recommendations and Actions Needed.

4 29 Appendix A: Disturbance Analysis Team ..32 In Appendix B: Detailed Review of Affected Appendix C: ERCOT June 26, 2021 Solar Plant Tripping Event ..49 nerc | Odessa Disturbance Report | September 2021 iv Preface Electricity is a key component of the fabric of modern society and the Electric Reliability Organization (ERO) Enterprise serves to strengthen that fabric. The vision for the ERO Enterprise, which is comprised of the North American Electric Reliability Corporation ( nerc ) and the six Regional Entities (REs), is a highly reliable and secure North American bulk power system (BPS).

5 Our mission is to assure the effective and efficient reduction of risks to the reliability and security of the grid. Reliability | Resilience | Security Because nearly 400 million citizens in North America are counting on us The North American BPS is made up of six RE boundaries as shown in the map and corresponding table below. The multicolored area denotes overlap as some load-serving entities participate in one RE while associated Transmission Owners (TOs)/Operators (TOPs) participate in another. MRO Midwest Reliability Organization NPCC Northeast Power Coordinating Council RF ReliabilityFirst SERC SERC Reliability Corporation Texas RE Texas Reliability Entity WECC WECC nerc | Odessa Disturbance Report | September 2021 v Executive Summary This report contains the ERO analysis of the BPS Disturbance that occurred in Texas on May 9, 2021, referred to herein as the Odessa Disturbance .

6 While the ERO has analyzed multiple similar events in California, this is the first Disturbance involving a widespread reduction of solar photovoltaic (PV) resource power output observed in the Texas Interconnection. The event involved solar PV facilities across a large geographic area of up to 200 miles away from the location of the initiating event. The Electric Reliability Council of Texas (ERCOT) provided Texas RE and nerc with a brief report as the Disturbance was categorized as a Category 1i In coordination with ERCOT, nerc and Texas RE gathered additional information from affected Generator Owners (GO) whose facilities experienced a notable reduction in power during the event.

7 In addition, nerc and Texas RE worked collaboratively with ERCOT and the impacted transmission service providers to gather additional information and corroborate incoming data with other sources. The purpose of this report is to document the analysis of the Disturbance and provide key findings and recommendations for industry. The Introduction provides details regarding the initiating event, performance of the BPS-connected solar PV fleet during the event, and additional details around the event. Chapter 1 provides a detailed review of the key findings and establishes the supporting evidence and technical basis for the recommendations that are laid out in Chapter 3.

8 In addition, Chapter 2 focuses on modeling and study findings that support the recommendations in Chapter 3. Appendix B provides a detailed analysis of the affected facilities. Appendix C describes analysis of a smaller event that subsequently occurred on June 26, resulting in solar PV resources tripping. Description of Disturbance At 11:21 Central time on May 9, 2021, a single-line-to-ground (Phase A) fault occurred on a generator step-up (GSU) transformer at a combined-cycle power plant near Odessa , Texas. The fault was caused by a failed surge arrester at the combustion turbine (CT) during startup for testing.

9 The circuit breaker for CT1 operated and cleared the fault within three cycles and the #2 unit experienced a partial trip followed by a run back for a total loss of 192 MW. The fault caused voltages in the area to drop to pu at the 345 kV connecting station for the generation facility, pu around Fort Stockton at a 138 kV station, and as low as pu at a 69 kV bus near Alpine, Texas. Voltage in the area recovered to near predisturbance levels very quickly (within a couple electrical cycles) after the fault cleared. In addition to the generation loss at the combined cycle plant, a number of solar PV and wind plants connected to the BPS also exhibited active power reductions caused by the fault event.

10 None of the affected inverter-based resources were tripped consequentially by the fault itself. Rather, all reductions were due to inverter-level or feeder-level tripping or control system behavior within the resources. Active power reductions by resource type are shown in Table Table : Reductions of Output by Unit Type Plant Type Reduction [MW] Combined Cycle Plant 192 Solar PV Plants 1,112 Wind Plants 36 Total 1,340 1 nerc Event Analysis Program: Executive Summary nerc | Odessa Disturbance Report | September 2021 vi Key Findings and Recommendations Refer to Chapter 1 and Chapter 2 for key findings from the event analysis and refer to Chapter 3 for specific recommendation outlined throughout this report.