Transmission System Planned Performance For Geomagnetic Disturbance Events

The 2025 Electric Reliability Organization (ERO) Enterprise Compliance Monitoring and Enforcement Program (CMEP) Implementation Plan identified extreme weather response as a risk element. One of the focus areas for this risk element is TPL-007-4 Transmission System Planned Performance for Geomagnetic Disturbance (GMD) Events, which are a rising concern for the Bulk Power System (BPS).

What is a geomagnetic disturbance (GMD)?

A GMD, or geomagnetic storm, is a major disturbance of Earth’s magnetosphere that occurs as a result of solar activity. Scientists can predict solar flares, but it is harder to determine if a solar flare will cause a GMD and what effects the event might have.

How does it affect the power grid?

In March 1989, a geomagnetic storm caused a power blackout in Québec, Canada. This storm caused a shutdown of the Hydro-Québec power system, leaving 6 million people without power for 9 hours.

The geomagnetic storm impact scale ranges from G1 to G5, with G5 being the most extreme classification. A G1, minor storm, could cause weak power grid fluctuations and minor impacts on satellites. A G1 aurora is commonly visible at high latitudes. A G5, extreme storm, could potentially cause blackouts or a complete collapse of power grids. A G5 aurora can reach latitudes as low as Florida and southern Texas.

On May 10-12, 2024, a G5 geomagnetic storm occurred, resulting in the largest GMD event in over two decades. The BPS remained stable throughout this event, but it caused some alarms to trigger and some transmission system components to trip offline. Some operators reduced power output in accordance with their procedures. Harmonic filters on a 345 kV transmission line in Western Canada tripped, and harmonic distortion may have contributed to the reported tripping of a 110 kV transmission line and the tripping of a 138 kV capacitor bank.

TPL-007-4 Transmission System Planned Performance for Geomagnetic Disturbance Events and Responsible Entity Roles

The Requirements below for TPL-007-4 are identified in the 2025 ERO Enterprise CMEP Implementation Plan. Additionally, the Electric Reliability Council of Texas (ERCOT) has provided a process that includes the Responsible Entity roles as it relates to TPL-007-4 in the ERCOT Planning Guide.

Requirement R1 states that each Planning Coordinator (PC) shall establish the individual and joint responsibilities of the PC and Transmission Planner (TP) for maintaining models, performing studies, and implementing processes.

R2 states that each responsible entity shall maintain System models and Geomagnetic-Induced Current (GIC) System models.

• According to the ERCOT Planning Guide, ERCOT, in collaboration with Transmission Service Providers (TSPs) and resource entities, develops and maintains the GIC system models.

R4 states that each Responsible Entity shall complete a benchmark GMD Vulnerability Assessment of the Near-Term Transmission Planning Horizon at least once every 60 calendar months. The benchmark shall use studies based on models identified in R2, document assumptions, and document summarized results of the steady state analysis.

• According to the ERCOT Planning Guide, each TSP and resource entity provides ERCOT (for use in the GMD Vulnerability Assessment) a list of equipment potentially removed from service as a result of protection system operations or misoperations due to harmonics that could result from benchmark or supplemental GMD events.

R5 states that each Responsible Entity provides GIC flow information to be used for the benchmark thermal impact assessment of transformers specified in Requirement R6 to each Transmission Owner (TO) and Generator Owner (GO) that owns an applicable Bulk Electric System (BES) power transformer in the planning area.

• According to the ERCOT Planning Guide, upon consideration of comments, ERCOT makes the GIC flow information available to TSPs and resource entities.

R7 states that each Responsible Entity that concludes (through the benchmark GMD Vulnerability Assessment conducted in Requirement R4) that their System does not meet the performance requirements for the steady state planning benchmark GMD event contained in Table 1, shall develop a Corrective Action Plan (CAP) addressing how the performance requirements will be met.

• According to the ERCOT Planning Guide, each TSP and Resource Entity, in collaboration with ERCOT, shall develop and document corrective action plans for the facilities.

Geomagnetic disturbance events have the potential to cause significant disruptions for the reliability of the BPS. If you have any questions regarding implementation of TPL-007-4 or any other Reliability Standards, please contact information@texasre.org.