FERC Proposes to Approve Revised GMD Reliability Standard

The Federal Energy Regulatory Commission (FERC) is poised to approve a revised reliability standard to ensure reliability during geomagnetic disturbances (GMDs).

FERC staff on May 17 issued a notice of proposed rulemaking (NOPR) urging its commissioners to approve Reliability Standard TPL-007-2, which the North American Electric Reliability Corp.(NERC) developed in response to FERC's September 2016-issued Order No. 830.

In Order No. 830, the commission approved TPL-007-1 (Transmission System Planned Performance for Geomagnetic Disturbance Events)-the currently effective reliability standard that establishes requirements for entities to assess transmission system vulnerabilities during GMDs. However, FERC also directed NERC to revise TPL-007-1's benchmark GMD event definition as it pertains to GMD vulnerability assessments and transformer thermal impact requirements so the definition would not be based solely on spatially averaged data.

NERC's revised reliability standard- TPL-007-2, which FERC staff proposed to approve last week-contains a supplemental higher, non-spatially-averaged reference peak geoelectric field amplitude component (12 V/km) than the benchmark GMD event definition (8 V/km). The revised standard-which applies to 280 generator owners and transmission owners, along with 188 planning coordinators and transmission planners-will require applicable entities to conduct supplemental GMD vulnerability assessments and thermal impact assessments on top of the currently required GMD vulnerability and transformer thermal impact assessments, which are based on the existing benchmark.

It will also require entities to obtain necessary geomagnetically induced currents (GIC) monitoring and magnetometer data as needed to enable model validation and situational awareness. Finally, it requires entities to develop necessary corrective action plans no later than a year after it completes the benchmark GMD vulnerability assessment, but it gives entities two years to deploy non-hardware mitigation, and four years to deploy hardware mitigation.

In the NOPR, FERC also proposed to direct NERC to develop and submit modifications to the reliability standard to require applicable entities to develop and implement corrective action plans to mitigate supplemental GMD event vulnerabilities.

According to FERC, the estimated annual cost of the revision to each affected entity varies from $409.70 (mostly for generator and transmission owners) to $2,738.84 (of planning coordinators and transmission planners). FERC said the cost "is not considered significant."

GMDs occur when the sun ejects charged particles that interact with and cause changes in the earth's magnetic fields. The interaction could cause GICs to cause damage to an electric power system. Depending on the design of a transformer and the magnitude and duration of a GMD event, GICs could cause heat damage to the condition, performance, and insulation life of a transformer.

However, studies offer mixed assessments of how widespread damage could be. (For more, see "Disaster Preparedness: The Quest for Transformer Resilience" in POWER'sApril 2018 issue). According to FERC, "depending on various factors affecting the intensity of the current, [GICs] can result in a risk of voltage instability or voltage collapse, as well as equipment loss or failure."

-Sonal Patel is a POWER associate editor (@sonalcpatel, @POWERmagazine)

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