By Rich Heidorn Jr.
ISO-NE has completed its work on the first two requirements to take effect under NERC’s revised geomagnetic disturbance (GMD) standard and will be fully compliant by the end of the year with requirements effective in July 2020, the RTO told the New England Power Pool’s Reliability Committee on Wednesday.
TPL-007-3 (Transmission System Planned Performance for Geomagnetic Disturbance Events) replaces TPL-007-1, effective July 1. TPL-007-3 added a regional variance for Canadian jurisdictions to TPL-007-2, which FERC approved in Order 851 in November (RM18-8, RM15-11-003). (See Revised NERC GMD Standard Approved.)
NERC developed the new standard in response to FERC’s directives to improve how its initial GMD rules, approved in 2016, addressed the risks from “locally enhanced” events. It broadens the definition of GMDs, requires grid operators to collect certain data and imposes deadlines for corrective actions.
The standard applies to planning coordinators (PCs), transmission planners (TPs) and transmission owners (TOs)/generator owners (GOs) with power transformer(s) with a high side, wye-grounded winding with terminal voltage greater than 200 kV.
NERC’s original standard required applicable entities to assess the vulnerability of their transmission systems to a “benchmark” GMD event — defined as a one-in-100-year event. 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. 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.
5 New Requirements
The standard adds five new requirements. R8, R9 and R10 require responsible entities to assess the potential implications of the supplemental GMD event on their equipment and systems. R8 requires the completion of a supplemental GMD vulnerability assessment at least once every five years. If the analysis finds the supplemental GMD event would cause cascading outages, the responsible entity must evaluate ways to reduce the likelihood or mitigate the impact of the event. NERC said its standard drafting team concluded that an evaluation was more appropriate than a formal corrective action plan “in light of the limitations of currently available tools for modeling localized GMD effects.”
R9 requires responsible entities to provide geomagnetically induced current (GIC) flow information based on the supplemental GMD event to owners of applicable bulk electric system power transformers in the planning area. R10 requires TOs and GOs to conduct a supplemental thermal impact assessment for BES power transformers where the maximum effective GIC value resulting from R9 is above a threshold (85 A per phase or greater).
Under R11 and R12, PCs and TPs must obtain GIC monitors and geomagnetic field data for their planning areas or system model areas. They must have at least one GIC monitor in their regions.
The new standard also made conforming changes to other requirements and revised the deadlines in R7 for corrective action plans required to address system performance issues identified in the benchmark vulnerability assessment.
ISO-NE’s Alex Rost said the RTO is already compliant with R1, which concerns the definition of PCs’ and TPs’ roles and responsibilities, and R2, maintaining system GIC models.
He said the RTO will be compliant by Dec. 1 with R5 (“Provide benchmark GIC flow information to applicable TOs and lead market participants [MPs] for applicable GOs”) and R9 (“Provide supplemental GIC flow information to applicable TOs and lead MPs for applicable GOs”), which take effect in January.
Rost said the analyses required by the standard can be “iterative” — results obtained in later stages of the study cycle may prompt the rerun of early-stage work.
He said most of the GIC modeling data required is already included in the New England system GIC model but that the RTO will notify applicable entities if modeling updates are needed.
