Geomagnetic Storm Effects on Transmission Elements Kenneth A. Donohoo,P.E. Oncor Electric Delivery Co LLC NERC GMDTF Chairperson

Introduction Space weather can affect the power system Large areas and multiple facilities can be affected Can happen at any time, not just at high sun spot activity Not just a northern latitude issue and can adversely impact ERCOT Higher voltage networks are more at risk Potential adverse impact on transformers, SVC’s and HVDC ties

Objectives At the completion of this course of instruction you will: recognize how a geomagnetic disturbance can impact the grid … be able to identify possible impacts and take action to prevent outages…

Definitions Coronal Mass Ejection (CME) is a massive burst of solar wind and magnetic fields rising above the solar corona or being released into space Geomagnetic Disturbances (GMD) are caused by intense solar activity that impacts the Earth’s geomagnetic field Changes to the geomagnetic field creates a voltage gradient and induces a Ground Induced Current (GIC – quasi DC) through any conductor

The Sun CME typically take 1 to 3 days to arrive on Earth May not head toward Earth

Sunspot Cycle Large GMD Storms can and do occur at anytime in the sunspot cycle and not just around the Sunspot peaks

Space Storm

Interactions

If the intensity and duration of a disturbance is sufficient, these abnormal electric currents may reduce system voltage and in the worst case, cause a widespread power outage. In the extreme, severe GIC can overheat transformer cores and lead to equipment damage or failure. Transformer harmonics increase Consume more reactive power, voltage decrease Trip capacitor banks, SVC’s, HVDC, etc… Relay misoperation

Some Storm History 19 th century first effects observed on compass needle Sept 1859, largest recorded, Carrington Event 18 hours to reach Earth Telegraph wires shocked operators and caused fires March 1989, Hydro Quebec Only took 92 seconds to blackout system Seven SVC’s tripped within 59 seconds of each other leading to voltage collapse 25 seconds later Six million people without power for nine hours Northern lights seen as far south as Texas

How do I find out about a solar storm? Information and Indications The following are triggers that could be used to initiate operator action: External to your company: NOAA Space Weather Prediction Center or other organization issues: Geomagnetic storm Watch (1-3 day lead time) Geomagnetic storm Warning (as early as minutes before a storm, and updated as solar storm characteristics change) Geomagnetic storm Alert (current geomagnetic conditions updated as k-index thresholds are crossed)

How do I find out about a solar storm? Information and Indications (continued) Internal to your company: System-wide: Reactive power reserves System voltage/MVAR swings/current harmonics Equipment-level: GIC measuring devices Abnormal temperature rise (hot-spot) and/or sudden significant gassing (where on- line DGA available) in transformers System or equipment relay action (e.g., capacitor bank tripping)

Actions Available to Operator The following are possible actions for Transmission Operators based on available lead- time: Long lead-time (1-3 days in advance, storm possible) 1.Increase situational awareness 1.Assess readiness of black start generators and cranking paths 2.Notify field personnel as necessary of the potential need to report to individual substations for on-site monitoring (if not available via SCADA/EMS) 2.Safe system posturing (only if supported by study; allows equipment such as transformers and SVCs to tolerate increase reactive/harmonic loading; reduces transformer operating temperature, allowing additional temperature rise from core saturation; prepares for contingency of possible loss of transmission capacity) 1.Return outaged equipment to service (especially series capacitors where installed) 2.Delay planned outages 3.Remove shunt reactors 4.Modify protective relay settings based on predetermined harmonic data corresponding to different levels of GIC (provided by transformer manufacturer).

Actions Available to Operator The following are possible actions for Transmission Operators based on available lead- time (continued): Day-of-event (hours in advance, storm imminent): 1.Increase situational awareness 1.Monitor reactive reserve 2.Monitor for unusual voltage, MVAR swings, and/or current harmonics 3.Monitor for abnormal temperature rise/noise/dissolved gas in transformers1 4.Monitor geomagnetically induced current (GIC2) on banks so-equipped3 5.Monitor MVAR loss of all EHV transformers as possible 6.Prepare for unplanned capacitor bank/SVC/HVDC tripping4 7.Prepare for possible false SCADA/EMS indications if telecommunications systems are disrupted (e.g., over microwave paths) 2.Safe system posturing (only if supported by study) 1.Start off-line generation, synchronous condensers 2.Enter conservative operations with possible reduced transfer limits 3.Ensure series capacitors are in-service (where installed)

Actions Available to Operator The following are possible actions for Transmission Operators based on available lead- time (continued): Real-time actions (based on results of day-of-event monitoring): 1.Safe system posturing (only if supported by study) 1.Selective load shedding5 2.Manually start fans/pumps on selected transformers to increase thermal margin (check that oil temperature is above 50° C as forced oil flow at lower temperatures may cause static electrification) 2.System reconfiguration (only if supported by study) 1.Remove transformer(s) from service if imminent damage due to overheating (possibly automatic by relaying) 2.Remove transmission line(s) from service (especially lines most influenced by GMD) Return to normal operation This should occur two to four hours after the last observed geomagnetic activity.

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