Q&A Series: Geomagnetic Disturbances and Power Outages Part IV
On January 15, 2013, I presented a webcast on Energy Central titled, “Geomagnetic Disturbances and their Impacts on Power Transformers”. You can view the presentation here.
The presentation generated many questions from the audience that I did not have time to address. This blog post addresses a few of those questions. Stay tuned for more blog posts with more questions and answers.
Question: What is the average age of power transformers in the US?
Answer: According to Hartford Steam Boiler, the average age of power transformers in the United States is approximately 40 plus years.
Question: What is IEEE doing about Geomagnetically Induced Currents (GIC) currents in transformers?
Answer: IEEE initiated a task force last year to look at GIC and determine its impact on transformers and the network. The purpose of the task force is to de-mystify issues surrounding GMD and the resulting GIC, present an accurate evaluation on the impacts of the GMD/GIC phenomena on equipment and networks and present a series of mitigating actions based on expert knowledge. Siemens is participating directly in this task force and others in conjunction with NERC.
Question: When will the IEEE task force report be issued?
Answer: NERC issued an interim whitepaper on GIC system impacts in January 2012. An expanded NERC task force is working on system reliability tool developments to deal with GMD impacts during storms and system planning tools to determine proper system configurations and mitigating measures.
The tool development is scheduled for completion by June 2014. Although that deadline is very aggressive, it is expected that the tool development and further GIC research will continue beyond that date.
IEEE-PES will be publishing a position paper on GIC equipment impacts, which will be presented at the GIC SuperSession of the 2013 Summer Power Meeting.
Question: What language should utilities put into transformer specifications to meet NERC requirements to address GMD in their specifications?
Answer: Specification of transformer's GIC requirement is straight-forward -- number of dc amps expected to flow in transformer neutral for a maximum (not continuous) duration.
However, development of the GMD storm scenario and system simulations to determine the amount of dc coupled into specific transmission locations is quite onerous.
In addition, it is important to note that the typical storm scenario is composed of many hours of low-level GIC flows, while the peak GIC pulse of concern has limited duration. Peak GICs have been observed for durations as short as a fraction of a minute, up to a maximum of only a few (3-5) minutes.
Question: FERC/NERC has backed off standards. Is that due to the complexity of the technology and determination of where to apply it?
Answer: Siemens has been working closely with FERC and NERC as well as IEEE and others to assist with practical approaches to dealing with GIC. There is certainly a lot of complexity involved. IEEE is actively working on the development of applicable standards for transformers.
Question: My understanding of the webinar material is that Siemens would not expect wide-spread, short-term failure of generator step-up transformer (GSU's) during a GMD. Correct?
Answer: This is correct. Of course, certain mitigation processes are recommended by NERC to avoid problems with system voltage collapse or relay mis-operation, which may be caused by wide-spread transformer saturation. However, in the case of saturation during a short duration GIC pulse, the transformer itself will not be harmed.
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