EPRI Research Summary relays solar storm activity results.
Press Release Summary:
SUNBURST monitoring system recorded minor levels of geo-magnetically induced currents (GIC) beginning at ~10:04 am EST on January 24, 2012 as a result of a solar flare that erupted early on January 23. During said event, only one SUNBURST site in the EPRI measurement system exceeded 10 A of DC current on neutral and did so for less than 1 min. Most GIC activity occurred between 10:04 am and 1:00 pm EST on January 24th, 2012. Activity continued through January 25th, but at much lower levels.
Original Press Release:
EPRI Research Summary - Results from Solar Storm Activity
Last week, the sun hurled billions of tons of plasma at up to 5 million mph toward Earth which produced a dazzling light display in northern regions of the world. Radiation from the explosion made the 93-million-million trip to Earth within 34 hours after the solar explosion. The event put the nation's utilities on alert for possible disruption of the power grid.
The Electric Power Research Institute (EPRI) measures geo-magnetically induced currents (GIC) through its SUNBURST program, a system of strategically positioned monitoring sites throughout the United States and Canada. It uses data from that system, to provide guidance to utilities on keeping the power delivery system functioning during solar storms and to provide feedback to those developing GIC models and forecasting tools. In the future, models of the power system, designed to evaluate the flow of GIC could be included to enhance the capability of the system.
The SUNBURST monitoring system recorded minor levels of GIC beginning at approximately 15:04 UT (10:04 am EST) on January 24, 2012. This was the result of a solar flare that erupted early on January 23rd. During this event, only one SUNBURST site in the EPRI measurement system exceeded 10 Amps of dc current on the neutral, and did so for less than one minute (GICs are quasi-dc and can cause saturation of transformer windings if the levels are high enough and last for extended periods currents less than 10 amps are generally considered to be low risk for causing transformer problems). Low-level GICs were measured at most other SUNBURST sites.
The largest dc currents generally coincided with the onset of the event. Most of the GIC activity occurred between 15:04 UT (10:04 am EST) and approximately 18:00 UT (1:00 pm EST) on January 24th, 2012. Activity continued through January 25th, but at much lower levels. Some sites recorded neutral dc currents that approached 5A twice during the first half of January 25th.
The following table lists the neutral current levels by site. Only sites that experienced significant GIC levels are included.
Central Hudson - Pleasant Valley: -5.2A to 8.6A
Central Hudson - Hurley Ave.: -6.2 to 5.5A
CMP/BHE - Chester: -6.5A to 5.5A
Manitoba Hydro - Grand Rapids: -9.1A to 9.7A
Con Edison of NY - Goethals: -9.4A to 4.7A
TVA - Paradise: -25.0 to 11.1A
National Grid Company-US - New Scotland: -2.7A to 1.5A
Included below are two sample plots of data recorded during this event.
Figure 1 - Plot showing 24 hours of neutral DC data at the Central Main Power/Bangor Hydro site in Maine
Figure 2 - Plot showing 1 hour of neutral dc data recorded from the start of activity at the TVA site in Kentucky
1. Characterizing Geomagnetic-Induced Currents during solar storms
This summary shows that the highest neutral currents measured during this storm event were at TVA's Paradise Substation, located in Kentucky and is further south than most of the other SUNBURST sites. Its GIC measurements have been among the highest recorded since a SUNBURST node was installed there less than a year ago. EPRI is investigating the Paradise phenomenon -- line impedance, length, orientation, and soil resistivity -- and will report any new developments. The data emerging from Paradise highlights the value and need of a wide area network capable of collecting both GIC measurement and magnetometer data.
An interesting feature in Figure 2 is the apparent transient nature of the maximum recorded GIC value. This initial spike typically occurs when the coronal mass ejection (CME) collides with the earth's magnetic field. Figure 3 below shows a comparison of the Paradise site with another location in the TVA service territory.
Figure 3: Comparison of GIC Values Recorded at Paradise and Sullivan Substations
The resolution of the data shown in Figure 3 is 5 seconds; thus, the peak GIC value was reached within a time span of 5 seconds. Note that this trend is shown in both sets of measurement data.
2. Assessing Vulnerability: System Planning Studies
System planning studies can be used to determine the impact of an extreme geomagnetic disturbance (GMD) on the grid. The studies can use a probabilistic approach based on the possible severity of a solar storm or an arbitrary severity can be assumed that has a very low probability of occurrence - for instance, some suggest evaluating the system against a 1 on 100 year storm. The block diagram below provides an approach for performing such studies on the transmission network.
GICs are quasi-dc currents created by induced voltages in the transmission lines. Because GICs are quasi-dc, they can be determined using a dc model of the network. The resulting GIC flows are used as inputs to time-domain transformer models which estimate the resulting var demand and harmonic current injection of the transformers. The var demand and harmonic current injection are then used as inputs to other system planning studies including: ac load flow, transient stability, power quality, and system protection.
Thermal models of the transformers are used to determine if individual transformers will exceed their thermal limits during a GMD. If the thermal limits of individual transformers are exceeded, they are considered vulnerable, and are removed from service for planning study purposes. Transformer and system vulnerability assessments are typically performed in parallel since the results of the two studies are co-dependent.
EPRI Research
EPRI is working with NERC and the utility industry to develop, among other things, the capability for utilities to assess the impact of an extreme GMD event on the grid. A few highlights of this research with regards to system planning studies are:
EPRI is also pursuing research in the following areas to assess and reduce the risk of geomagnetic disturbances:
Improved storm warning to increase forecasting accuracy and lead times. This effort involves collaboration among experts, with EPRI SUNBURST data providing key inputs into improved forecasting models. EPRI also is working with the North American Electric Reliability Corporation (NERC) on a project to develop a continental model that will help clarify likely impacts on the grid.
Increased real-time system awareness to support informed utility operations during storm conditions. EPRI is exploring three research areas to increase such awareness. The first is research assessing the use of existing microprocessor-based relays to estimate GIC and transformer response by directly measuring harmonics and voltage in real time. The second is research to explore the use of EPRI's existing network of power quality monitors to examine harmonic generation in transformers during solar storms. The third is research on meaningful signal analysis of these data streams to allow an accurate assessment of the risk to a specific transformer and the risk to the grid as a whole. In addition, the data will serve as valuable input into future storm forecasting and assist with forensics of failed equipment.
Increased utility collaboration. EPRI has established an interest group to shape the research portfolio, better understand geomagnetic disturbances and other high-impact low-frequency (HILF) events; and share and document current industry best practices.
Key technical contacts on the subject at EPRI are:
Rich Lordan, P.E. 650-855-2435 rilordan@epri.com
Randy Horton, Ph.D., P.E. 205-424-3927 rhorton@epri.com
About EPRI
The Electric Power Research Institute, Inc. (EPRI, www.epri.com) conducts research and development relating to the generation, delivery and use of electricity for the benefit of the public. An independent, nonprofit organization, EPRI brings together experts from academia and industry as well as its own scientists and engineers to help address challenges in electricity generation, delivery and use, including health, safety and the environment. EPRI's members represent more than 90 percent of the electricity generated and delivered in the United States, and international participation extends to 40 countries. EPRI's principal offices and laboratories are located in Palo Alto, Calif.; Charlotte, N.C.; Knoxville, Tenn.; and Lenox, Mass.
Contact:
Don Kintner
EPRI
Manager, Communications
dkintner@epri.com
704-595-2506
