Geomagnetic disturbances feel like an exotic topic until you realize the exam treats EOP-010 like any other emergency-preparedness standard: know who owns what, know the physics chain, and know what the mitigation actions look like from the desk. Solar storms are also one of the few exam topics where a single historical event — Hydro-Québec, 1989 — anchors almost every concept you need.
Test Tips
- Nail the RC/TOP split. Under EOP-010-1, the Reliability Coordinator develops, maintains, and implements the GMD Operating Plan for its RC Area (R1), and the Transmission Operator develops, maintains, and implements its own GMD Operating Procedure or Operating Process (R3). Exam distractors routinely swap these two — if the question says “Plan,” think RC; if it says “Procedure or Process,” think TOP.
- Know the information-flow requirement. EOP-010-1 R2 makes the RC responsible for disseminating forecasted and current space weather information to the functional entities identified as recipients in its GMD Operating Plan. “Each entity monitors space weather on its own” is a distractor — the standard puts the dissemination duty on the RC.
- Operations vs. planning trap. EOP-010 covers the operating horizon. GMD vulnerability assessments and planned performance belong to the TPL-007 family on the planning side. If the question mentions “assessment of system performance for a benchmark GMD event,” that is planning, not EOP-010.
- Memorize the physics chain. A GMD drives geomagnetically induced currents (GIC) — quasi-DC current — into the grid through grounded-wye transformer neutrals. That causes half-cycle saturation of transformers, which produces hot-spot heating, harmonics, and sharply increased reactive power absorption. The reliability concern is voltage — depressed voltage and potential voltage instability — not frequency. Distractors that make GMD a “frequency problem” are wrong.
- Know what mitigation looks like. Typical GMD operating actions: postpone planned maintenance and return transmission elements to service, reduce loading on affected transformers and long lines, position additional reactive reserves, and stay alert for capacitor bank and SVC trips caused by harmonics. In the 1989 Hydro-Québec event, harmonic-driven SVC trips led to voltage collapse in well under two minutes — a favorite exam anecdote.
- Applicability threshold. EOP-010-1 applies to Reliability Coordinators and to Transmission Operators whose area includes a power transformer with a high-side, wye-grounded winding with terminal voltage greater than 200 kV. That 200 kV wye-grounded detail shows up as an answer choice.
5 Practice Questions
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Under EOP-010-1, which functional entity is responsible for developing, maintaining, and implementing a GMD Operating Plan that coordinates GMD mitigation activities within its area?
A. Transmission Operator
B. Balancing Authority
C. Reliability Coordinator
D. Generator Operator -
A significant geomagnetic storm is forecast. Under EOP-010-1, the Reliability Coordinator must disseminate forecasted and current space weather information to:
A. All registered entities in the Interconnection
B. The functional entities identified as recipients in its GMD Operating Plan
C. Adjacent Reliability Coordinators only
D. NERC and the Regional Entity -
What is the primary mechanism by which geomagnetically induced currents (GIC) stress the Bulk Electric System?
A. They raise system frequency above scheduled frequency
B. They cause half-cycle saturation of transformers, producing heating, harmonics, and increased reactive power absorption
C. They lower the impedance of long transmission lines
D. They reverse real power flow on interchange schedules -
Which action is MOST consistent with a Transmission Operator’s GMD Operating Procedure during a strong geomagnetic storm?
A. Immediately shed firm load when any storm warning is received
B. Postpone planned maintenance outages and reduce loading on affected transformers
C. Update the long-term planning assessment for a benchmark GMD event
D. Suspend three-part communication to shorten directive delivery time -
EOP-010-1 applies to a Transmission Operator whose Transmission Operator Area includes:
A. Any transformer rated above 100 kV
B. A power transformer with a high-side, wye-grounded winding with terminal voltage greater than 200 kV
C. Any generation resource larger than 75 MVA
D. All Transmission Operators, with no equipment threshold
Answer Key & Explanations
- C. EOP-010-1 R1 assigns the GMD Operating Plan to the Reliability Coordinator. The TOP’s obligation is a GMD Operating Procedure or Operating Process under R3 — different document, different entity.
- B. EOP-010-1 R2 requires the RC to disseminate forecasted and current space weather information to the recipients identified in its GMD Operating Plan — not to every registered entity, and not only to neighboring RCs.
- B. GIC is quasi-DC current entering through grounded-wye transformer neutrals. Half-cycle saturation drives hot-spot heating, harmonic generation, and heavy var absorption — a voltage problem, not a frequency problem.
- B. Conservative operations — deferring maintenance, restoring elements to service, and unloading vulnerable transformers — are the classic GMD procedure actions consistent with EOP-010-1 R3. Planning assessments (choice C) are a planning-horizon activity, and load shed is not an automatic first response to a storm warning.
- B. The applicability section of EOP-010-1 covers TOPs whose area includes a power transformer with a high-side, wye-grounded winding with terminal voltage greater than 200 kV — the configuration that gives GIC a path into the transformer.
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