The Southwest Power Pool on July 9 published its report on the April 26 load-shed event in Northwest Louisiana that analyzes the event, identifies the main causes that led to the need to shed load, examines how SPP responded during and after the event, and provides recommendations and improvements to prevent similar incidents from occurring in the future.
“We recognize the impact the April 26 power outages had on communities in Northwest Louisiana. Our detailed analysis has identified specific areas for improvement, and we are actively working with the affected utilities to address those areas. We remain firmly committed to supporting our member companies in keeping communities reliably powered," said SPP President and CEO Lanny Nickell, in a statement.
Background
On Saturday, April 26, 2025, SPP identified instability on the bulk power grid in northwest Louisiana.
In accordance with its emergency operating procedures, and to prevent more widespread impacts, SPP instructed American Electric Power Service Corporation (AEPSC) as agent for Southwestern Electric Power Company (SWEPCO), one of its seven regional electric utilities, to immediately reduce electricity use by 140 megawatts in SWEPCO’s Northwest Louisiana service territory, leading to an interruption of service that affected approximately 30,000 residential and business customers.
SPP acts as a North American Electric Reliability Corporation-approved Reliability Coordinator (RC) and Balancing Authority (BA) for the region in northwest Louisiana impacted on April 26.
The unique roles of the RC, BA, Regional Transmission Operator, and Transmission Operator (TOP) “are fundamental to understanding the operational responsibilities and coordination efforts discussed throughout the rest of this report,” SPP said in the report.
Recognizing the relationships between RTO, BA, RC and TOP responsibilities “provides essential insight into how the transmission system is managed to maintain reliability and security across the grid.”
Overview of event
On April 26, SPP observed insufficient reactive power support and voltage stability in the Shreveport, Louisiana, area.
Reactive power works in conjunction with real power to keep voltage levels on the transmission system steady; when it’s lacking, there’s a higher risk of voltage problems or outages, the grid operator said.
“As prescribed by its emergency operating procedures, SPP worked to mitigate the risk that this voltage instability could cause uncontrolled, more widespread outages in AEP-SWEPCO’s northwest Louisiana service territory,” the report said.
Service interruptions like the one instructed on April 26 are used only as a last resort when all other solutions to reliability threats have been exhausted, the report said.
“SPP’s order for curtailment of 140 MW of electricity mitigated the risk of severe cascading outages that could have resulted in hundreds of thousands of customers being in the dark for a longer period,” the report said.
Conditions ultimately led SPP to instruct AEP-SWEPCO to immediately shed 140 MW of load in the impacted area to maintain overall system reliability.
Once the order for curtailment was given, the AEP-SWEPCO system operators had only minutes to initiate load shed actions to address grid conditions,
The instruction resulted in the loss of power for approximately 30,000 customers for approximately six hours in AEP-SWEPCO’s footprint, primarily in the parishes of Caddo and Bossier.
Emergency protocols established by NERC necessitate that RCs instruct the curtailment of electricity use to prevent the possibility of uncontrollable cascading system collapses.
These emergency protocols are governed by NERC, which enforces standards related to the reliable operation of the U.S. bulk electric system, SPP said.
“Circumstances on April 26 were such that risks resulting from local voltage instability in northwest Louisiana could only be addressed by curtailing electricity use in the immediate area. AEP-SWEPCO was required to follow SPP’s instructions to maintain the controlled outage until SPP and AEP-SWEPCO jointly determined the system was no longer at risk.”
Factors Contributing to the Need to Shed Load
SPP’s post-event review highlighted two primary operational factors that led to the need to shed load.
“In simple terms, SPP’s ‘early-warning radar’ did not predict the voltage issues that later materialized and required emergency action. Higher than forecasted temperatures caused increased loading on the system, which ultimately caused voltage concerns for the area,” the report said.
Once the voltage issues materialized in real-time, SPP worked closely in its capacity as an RC with AEP-SWEPCO as the TOP to identify all possible mitigation measures prior to instructing the load shed. The two entities considered alternative mitigation measures that included transmission, generation, and load switching options.
Ultimately, though, no other measure could provide enough relief to mitigate the need for immediate reduction in load, SPP said.
The second factor contributing to the need to shed load was an insufficient operating margin in a region identified as a “load pocket” into which only limited amounts of energy can be imported due to transmission constraints.
These constraints were compounded by planned and SPP-approved maintenance outages of approximately 3,000 MW of generation and two transmission facilities in the area being out of service.
Maintenance outages are coordinated months in advance between SPP and TOPs throughout the region, SPP said.
SPP assesses requests for planned maintenance outages using processes that consider weather and load forecasts among many other variables.
Additionally, SPP’s Operational Planning Analysis (OPA), Voltage Security Assessment Tool (VSAT) and other forward-looking studies are meant to identify contingencies far enough in advance that adequate transmission and generation facilities can be brought and/or kept online to ensure system reliability.
“In this case, months-earlier forecasts were such that local facilities were allowed to take seasonal maintenance outages, and OPA and VSAT processes failed to identify the developing voltage instability early enough to bring additional long startup-time generating or other reactive power facilities online to mitigate risks.”
As such, once SPP’s real-time analyses began to reveal the emerging voltage instability conditions, the SPP and AEP-SWEPCO worked together to determine appropriate and timely actions needed to maintain a stable electric grid, though limited mitigation options were available, the report said.
The report also includes lessons learned and recommendations.
