From Impact of Severe Solar Flares, Nuclear EMP and Intentional EMI on Electric Grids by John G Kappenman (40 pages)
HEMP Fast Pulse exposure covers a total of 1765 substations exposed or ~83% of 2106 major HV and EHV substations. In addition some 35,000 to 40,000 Distribution Class Substations may also be of concern for Fast Pulse Exposure.
Transformers were seen as a potential problem to the grid as far back as 1990, said Sarah Mahmood, a program manager at the Department of Homeland Security, which paid for about half of the cost of the $17 million drill, with the rest picked up by the electrical industry. Transformers are about the size of a one-car garage
For the test, the Electric Power Research Institute ordered three “recovery transformers” from a supplier, ABB in St. Louis. This week they were trucked to a substation owned by CenterPoint Energy near Houston.
Ordinary transformers are often too big and heavy to travel by road, and they require special rail cars. But because the transformers typically last 50 years, only a few dozen are shipped each year, so even the appropriate rail cars are in short supply. Ratcheting up the degree of difficulty, many of the places where a replacement transformer might have to go are no longer served by rail.
So the research institute tried a different approach, substituting three smaller, more mobile transformers for one conventional one, and specifying a size that would fit on a modified truck trailer. (A standard transformer costs roughly $5 to $7 million; buying and combining the three singles is slightly more expensive.)
Using a different transformer for each phase allowed shrinking the weight of the transformer from about 400,000 pounds for a single one to roughly 125,000 pounds for each of the three-phase units. In operation, the transformers are oil-filled, but in this case, the oil was shipped in tanker trucks in the convoy, to decrease weight.
With three transformers, three crews can work simultaneously to set them up, and setting up a small transformer is faster than setting up a big one.
In addition, installing a transformer usually requires pouring a concrete foundation, but one of these transformers was mounted on skids, eliminating that need..
Even with all these shortcuts, there were speed bumps. One is that utility executives think a stockpile is a good idea, but nobody is quite sure what to stockpile, or where.
The industry rule of thumb is that for every 13 transformers in the field, there are 10 designs. And the initial model that they will stockpile will only work as a replacement for about 500 of the 2,100 transformers in the system.
The next step will be a transformer unlike almost any in the field, that can be configured to work between more than two different voltages — say, operating not just between 138 kilovolts and 345 kilovolts, but also between 115 kilovolts and 345 kilovolts. That would cover a few hundred more.
Geomagnetic Storm Levels
•Impacts on North American Power Grid on March 13-14, 1989 occurred at disturbance intensities of ~300-500 nT/min
•Disturbance intensities of >2000 nT/min have been observed at latitudes of concern for US power grid infrastructure on at least 3 occasions since 1972
•Disturbance intensity of ~5000 nT/min was estimated for storm on May 14-15, 1921 (estimated to be largest storm of 20thCentury and comparable to Carrington Event of 1859)
•Power Grids should expect Storms 4 to 10 Times More Intense than the March 1989 Storm
South Africa (Eskom) had episodic EHV Transformer Failures due to Oct-Nov 2003 Geomagnetic Storms (5 Major Stations, 15 Large Transformers Failures –~13% of System EHV Transformers. Equal to the 1989 event in intensity but longer in duration.
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