Thursday, February 21, 2019

Revised NERC GMD Standard Approved

By Rich Heidorn Jr.

FERC on Thursday approved NERC’s revised geomagnetic disturbance reliability standard, which broadens the definition of GMDs, requires grid operators to collect certain data and imposes deadlines for corrective actions (RM18-8, RM15-11-003).

NERC created Reliability Standard TPL-007-2 (Transmission System Planned Performance for Geomagnetic Disturbance Events) in response to FERC’s directives to improve how its initial GMD standard, approved in 2016, addressed the risks from “locally enhanced” events. (See FERC Pushes NERC Further on GMD Rules.)

GMD storm in Fairbanks, Alaska, April 2011 | NASA

Thursday’s order (Order 851) directed NERC to revise the standard further to require the implementation of corrective action plans for responding to vulnerabilities to “supplemental” GMD events and to authorize case-by-case extensions of deadlines on corrective action plans. The commission also accepted NERC’s revised GMD research work plan.

‘Supplemental’ GMD Events

GMDs occur when the sun ejects charged particles that cause changes in Earth’s magnetic fields, potentially causing geomagnetically induced currents (GIC) that can cause voltage instability or collapse, damaging connected equipment.

NERC’s original standard required applicable entities — planning coordinators, transmission planners, transmission owners and generation owners connected at 200 kV or higher — to assess the vulnerability of their transmission systems to a “benchmark GMD event.” The benchmark was defined as a one-in-100-year event that would cause an 8-V/km “reference peak geoelectric field amplitude” at 60 degrees north geomagnetic latitude using Quebec’s ground conductivity.

Entities that fail to meet certain performance requirements based on the results of the benchmark assessment must implement corrective action plans.

Potential impacts of geomagnetic disturbances on the transmission system | PJM

The new standard addresses FERC’s directive to revise the benchmark GMD event definition so that it is not based solely on the averaging of magnetometer readings over a geographic area. Going forward, entities will have to conduct vulnerability and thermal impact assessments on “supplemental” events.

NERC defined the supplemental GMD event using individual station measurements rather than spatially averaged measurements, acknowledging that geomagnetic fields during severe GMD events can be “spatially non‐uniform” with localized peaks that could affect reliability. The supplemental GMD event definition contains a higher, non-spatially averaged reference peak geoelectric field amplitude component than the benchmark event definition (12 V/km versus 8 V/km).

The new rule also requires the collection of GIC monitoring and magnetometer data and adds a one-year deadline for the completion of corrective action plans and two- and four-year deadlines for completing mitigation involving non-hardware and hardware, respectively.

Case-by-Case Review

NERC had proposed allowing entities to exceed deadlines for corrective actions when “situations beyond the control of the responsible entity [arise],” which FERC said was inconsistent with its prior directive that extensions be considered on a case-by-case basis.

“While we generally agree with the standard of review that NERC states it will use to assess the merits of extension requests, we conclude that such assessments should be made before any time extensions are permitted,” the commission said. “By requiring prior approval of extension requests, the modified reliability standard will limit the potential for unwarranted delays in implementing corrective action plans while also providing NERC with an advance and more holistic understanding of where, to whom and for how long extensions are granted.”

Additional Directives

FERC said NERC did not go far enough in the revised standard, which requires entities to assess supplemental GMD event vulnerabilities but not to implement corrective action plans to address them. NERC would have required entities only to make “an evaluation of possible actions to reduce the likelihood or mitigate the consequences and adverse impacts of the events if a supplemental GMD event is assessed to result in cascading.”

FERC disagreed with commenters who said requiring corrective action plans is premature. “We see no basis, technical or otherwise, for not requiring corrective action plans for assessed supplemental GMD event vulnerabilities,” the commission said.

The rule is effective 60 days after publication in the Federal Register.