ImageOn 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. This is the fifth and final article in a series I have written attempting to answer all the questions from that event. You can view my other posts here:

 

Question: Will global warming affect the likelihood of a Geomagnetic Disturbance (GMD) event?

Answer: We are aware of no indication that global warming will affect the likelihood of a GMD event.  For further details, please refer inquiries to NOAA regarding whether a linkage is possible between atmospheric geomagnetic disturbances and land/sea surface temperatures.

Question: Are distribution transformers more susceptible if they have a high amount of solar generated electricity?

Answer: Distribution transformers are less susceptible to Geomagnetically Induced Currents (GIC), because they are attached to shorter line lengths and lower voltages. Regarding power transformer susceptibility, the type of loading (e.g. solar vs. conventional power) has no influence on GIC susceptibility. However, lightly loaded transformers have greater thermal margin and, therefore, can sustain larger amounts of GIC without overheating. 

Question: Is there a website that forecasts GMD?

Answer: Yes. There are a number of national and international forecasting organizations. In the US, please refer to NOAA. 

Question: Some have resisted adding protection devices because they consider them more risky?  What is that about?

Answer: While many mitigation devices have been proposed and some even developed, there is still a general concern from users about the effectiveness, cost, reliability and system impact of adding these devices on a large scale.

In particular, users are concerned that improperly designed blocking devices might actually decrease the system's reliability. It is important that the mitigation hardware properly operate in a grounded neutral configuration on a continuous basis, yet safely transition to the ungrounded configuration during the GMD event. 

This bi-state operation is a tough hurdle to achieve reliably, and it is natural that it takes time for users to become comfortable with a new technology before adopting it. 

Question: Why don’t we just use current blockers on all transformer neutral connections?

Answer: Current blockers are not a “one size fits all” solution. However, they may be effective in preventing damage to high risk, critical assets, which are susceptible to GIC-related damage, such as older transformers with very little insulation life left.

Also, current blockers still have to allow for normally grounded operation when GMD is not occurring. This complicates their operation and adds to significant cost. Furthermore, the effect on the network of the large scale use of current blockers is not yet known. For example, if hundreds of neutral blockers are added, the induced dc current will continue to flow. This begs the question, “What new locations in the network will be affected?”

Question: Could you tell us about GIC Modeling Software availability? And, also given the known real time DC current through transformer, would it be difficult to model the expected temperature rises due to core saturation.

Answer: There are several GIC modeling software programs available, but none that we are aware of that can predict the magnitude of a storm or the thermal impact on transformers. The possibility of thermal damage of a transformer during an event needs to be evaluated on a case-by-case basis, taking into consideration the difference in designs and equipment health.

Having said that, it could be possible to model the expected temperature rise in a transformer but only if the transformer model was available. Since every transformer's design from each manufacturer is different, a model would have to be developed on a case-by-case basis.

Siemens has recently released a GIC modeling module for its highly successful PSS®E suite of software. This module has provision to perform many network calculations of GIC at various storm strengths and directions. However, while the PTI GIC modeling module can be used to model power system GIC flows, it does not model the transformer's thermal response.

Information about the Siemens PSS®E GIC module can be found here. 

Going Forward

Thank you again for engaging in a conversation about this interesting and emerging topic. I do hope that some of my answers have been helpful to you. And, I encourage you to keep the conversation going with your own questions or expertise on the topic.