FERC approves reliability standard involving GMDs

FERC on Sept. 22 approved Reliability Standard TPL-007-1, establishing requirements for certain registered entities to assess the vulnerability of their transmission systems to geomagnetic disturbance events (GMDs), which occur when the sun ejects charged particles that interact with and cause changes in the earth’s magnetic fields.

Applicable entities that do not meet certain performance requirements, based on the results of their vulnerability assessments, must develop a plan to achieve the performance requirements, FERC added in its order.

FERC also directed NERC, which submitted the reliability standard for FERC approval, to develop modifications to the standard to:

  • Modify the benchmark GMD event definition set forth in “Attachment 1” of the reliability standard as it pertains to the required GMD vulnerability assessments and transformer thermal impact assessments, so that the definition is not based solely on spatially averaged data
  • Require the collection of necessary geomagnetically induced current monitoring and magnetometer data and to make such data publicly available
  • Include a one-year deadline for the development of corrective action plans and two- and four-year deadlines to complete mitigation actions involving non-hardware and hardware mitigation, respectively

FERC also directed NERC to submit a work plan and, subsequently, one or more informational filings that address specific GMD-related research areas.

FERC noted that the reliability standard addresses the directives in Order No. 779 by requiring applicable bulk-power system owners and operators to conduct initial and ongoing vulnerability assessments regarding the potential impact of a benchmark GMD event on the bulk-power system as a whole and on bulk-power system components. Potential mitigation strategies identified in the reliability standard include the installation, modification or removal of transmission and generation facilities and associated equipment, FERC said.

Order 779 directed NERC to implement the directive in two stages, FERC said, adding that in the first stage, it directed NERC to submit, within six months of the effective date of Order 779, one or more reliability standards (First Stage GMD Reliability Standards) that require owners and operators of the bulk-power system to develop and implement operational procedures to mitigate the effects of GMDs consistent with the reliable operation of the bulk-power system.

In the second stage, FERC said that it directed NERC to submit, within 18 months of the effective date of Order 779, one or more reliability standards (Second Stage GMD Reliability Standards) that require owners and operators of the bulk-power system to conduct initial and ongoing assessments of the potential impact of benchmark GMD events on bulk-power system equipment and the bulk-power system as a whole.

FERC directed that the Second Stage GMD Reliability Standards must identify benchmark GMD events that specify what severity of GMD events a responsible entity must assess for potential impacts on the bulk-power system. FERC added that Order 779 explained that if the assessments identified potential impacts from benchmark GMD events, the reliability standards should require owners and operators to develop and implement a plan to protect against instability, uncontrolled separation, or cascading failures of the bulk-power system, caused by damage to critical or vulnerable bulk-power system equipment, or otherwise, as a result of a benchmark GMD event.

FERC also noted that it directed that the development of that plan could not be limited to considering operational procedures or enhanced training alone but should, subject to the potential impacts of the benchmark GMD events identified in the assessments, contain strategies for protecting against the potential impact of GMDs based on factors such as the age, condition, technical specifications, system configuration or location of specific equipment.

FERC said that Order 779 observed that those strategies could, for instance, include automatically blocking geomagnetically induced current (GIC) from entering the bulk-power system, instituting specification requirements for new equipment, inventory management, isolating certain equipment that is not cost-effective to retrofit or a combination thereof.

FERC noted that NERC maintains that the reliability standard is just, reasonable, not unduly discriminatory or preferential and in the public interest. According to NERC, the reliability standard applies to planning coordinators, transmission planners, transmission owners and generation owners who own or whose planning coordinator area or transmission planning area includes a power transformer with a high side, wye-grounded winding connected at 200 kV or higher.

In a Sept. 22 statement, NERC said that reliability is a priority for NERC and industry, and that it will continue the work with FERC and stakeholders toward assuring the reliability of the North American bulk power system.

Among other things, FERC said in its order that the reliability standard contains seven requirements:

  • Requirement R1 requires planning coordinators and transmission planners to determine the individual and joint responsibilities in the planning coordinator’s planning area for maintaining models and performing studies needed to complete the required GMD vulnerability assessment 
  • Requirement R2 requires planning coordinators and transmission planners to maintain system models and GIC system models needed to complete the required GMD vulnerability assessment
  • Requirement R3 requires planning coordinators and transmission planners to have criteria for acceptable system steady state voltage limits for their systems during a certain benchmark GMD event
  • Requirement R4 requires planning coordinators and transmission planners to conduct the GMD vulnerability assessment every 60 months using a certain benchmark GMD event. The benchmark GMD event is based on a 1-in-100 year frequency of occurrence and is composed of four elements: a reference peak geoelectric field amplitude of 8 V/km derived from statistical analysis of historical magnetometer data; a scaling factor to account for local geomagnetic latitude; a scaling factor to account for local earth conductivity; and a reference geomagnetic field time series or wave shape to facilitate time-domain analysis of GMD impact on equipment. The product of the first three elements is referred to as the regional geoelectric field peak amplitude
  • Requirement R5 requires planning coordinators and transmission planners to provide GIC flow information, to be used in a required transformer thermal impact assessment, to each transmission owner and generator owner that owns an applicable transformer within the applicable planning area
  • Requirement R6 requires transmission owners and generator owners to conduct thermal impact assessments on solely and jointly owned applicable transformers where the maximum effective GIC value provided in Requirement R5 is 75 amperes per phase (A/phase) or greater
  • Requirement R7 requires planning coordinators and transmission planners to develop corrective action plans if the GMD vulnerability assessment concludes that the system does not meet certain performance requirements

During the commission’s Sept. 22 meeting, FERC Chairman Norman Bay said, “We know that GMD poses a risk to the grid, but we also know that the science of GMD continues to evolve as scientists deepen their understanding of how GMD would impact the grid and how its effects can be mitigated. … As the science develops, the commission should reexamine the standard to ensure that we are striking the right balance.”

Commissioner Cheryl LaFleur said that GMD “is exactly the kind of high-impact, low-frequency, broad-based threat to the grid that only the government, in a regulatory role, with NERC participating, can really handle.”

She said, “[T]he challenge we had was balancing the need for action on something that could pose a very big threat, but with a recognition that the science was very much still evolving, as well as the engineering understanding of how solar storms actually impact the grid, and I hope we struck a very good balance in the final rule.”

Commissioner Tony Clark said that these naturally occurring magnetic field disturbances are sort of like earthquakes in that on any given day, it is probably a low probability that a major earthquake will occur, but there is a high probability that somewhere over the course of time, there will be one of these type of events. While they are truly infrequent, they have the potential for being a major impact, and so FERC takes it seriously, he said.

Commissioner Colette Honorable said that the final rule is an important step in addressing the risks posed by GMD events to the bulk power system. She said that the rule also recognizes that the potential impacts of GMDs on reliability are evolving and will evolve over time and that continued GMD research is necessary.

About Corina Rivera-Linares 3286 Articles
Corina Rivera-Linares was TransmissionHub’s chief editor until August 2021, as well as part of the team that established TransmissionHub in 2011. Before joining TransmissionHub, Corina covered renewable energy and environmental issues, as well as transmission, generation, regulation, legislation and ISO/RTO matters at SNL Financial from 2005 to 2011. She has also covered such topics as health, politics, and education for weekly newspapers and national magazines.