Geomagnetic Storm Effects on Transmission Elements

Kenneth A. Donohoo,P.E.Oncor Electric Delivery Co LLC

NERC GMDTF Chairperson

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

Space Storm

Interactions

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 increaseConsume more reactive power, voltage decreaseTrip capacitor banks, SVC’s, HVDC, etc…Relay misoperation

Some Storm History19th century first effects observed on compass needleSept 1859, largest recorded, Carrington Event

18 hours to reach EarthTelegraph wires shocked operators and caused fires

March 1989, Hydro QuebecOnly took 92 seconds to blackout systemSeven SVC’s tripped within 59 seconds of each other

leading to voltage collapse 25 seconds laterSix million people without power for nine hoursNorthern lights seen as far south as Texas

How do I find out about a solar storm?

Information and IndicationsThe 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 15-60 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 OperatorThe 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 awareness1. Assess readiness of black start generators and cranking paths2. 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 outages3. Remove shunt reactors4. Modify protective relay settings based on predetermined harmonic data

corresponding to different levels of GIC (provided by transformer manufacturer).

Actions Available to OperatorThe following are possible actions for Transmission Operators based on available lead-time (continued):

 Day-of-event (hours in advance, storm imminent):

1.Increase situational awareness1. Monitor reactive reserve2. Monitor for unusual voltage, MVAR swings, and/or current harmonics3. Monitor for abnormal temperature rise/noise/dissolved gas in transformers14. Monitor geomagnetically induced current (GIC2) on banks so-equipped35. Monitor MVAR loss of all EHV transformers as possible6. Prepare for unplanned capacitor bank/SVC/HVDC tripping47. 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 condensers2. Enter conservative operations with possible reduced transfer limits3. Ensure series capacitors are in-service (where installed)

Actions Available to OperatorThe 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 shedding52. 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.

QuestionsQuestions

????