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Cold Weather Reliability Standards - Are We Safe Now?

Now that the industry has rushed to develop new cold weather NERC standards, it is time to look at what we have accomplished. We should ask ourselves: “Is it likely that these standards will prevent a repeat of the impact of Winter Storm Uri on the grid?” To answer this question, a detailed analysis should be performed, with a focus on the impacts of EOP-012-1.


The drafting of this standard should have been a data driven effort. Plenty of data has been provided to FERC and NERC. It is reasonable to expect that such a high-profile standard would have sufficient FERC and NERC support staff to analyze the data and provide results to the Standard Drafting Team (SDT). That team can then utilize these results for the development of an effective standard. Unfortunately, due to the rush to implement a new standard, NERC and FERC have provided neither the data nor the resources necessary to perform an evaluation of the data from Winter Storm Uri to help guide the development of EOP-012-1.


The SDT drafted EOP-012-1 without the benefit of data analysis. The requirements of EOP-012-1 expect generators to be able to operate (at least for a few hours) at temperatures down to the calculated Extreme Cold Weather Temperature (ECWT) for their location. ECWT is defined as the temperature equal to the lowest 0.2 percentile of the hourly temperatures measured in December, January, and February, using a dataset from January 1, 2000, through the date the temperature is calculated.


In an effort to perform some analysis, we calculated the ECWTs for 10 Texas cities and 6 cities in the surrounding states. Then we assessed these ECWTs against the temperatures experienced during Winter Storm Uri. Our findings are summarized in the table below. Note that in each case, the temperature remained at or below the ECWT for between 8 and 48 hours.


*In degrees F. All temperature data was rounded to the nearest tenth of a degree.

Weather data was acquired from: https://mesonet.agron.iastate.edu/request/download.phtml


If generators are only capable of operating to their ECWT for a few hours, there is a high probability that generators will have freeze issues during a repeat of Winter Storm Uri. Freezing occurs due to overall (net) heat loss from a system. The longer that a system is losing heat, the more likely that a freeze event will occur.


Winter Storm Uri will likely not be the most severe winter storm we will experience. Of the 16 cities we analyzed, Hot Springs, AR had the shortest duration below its ECWT (8 hours) during Uri, however, it then experienced 19 hours below its ECWT in December 2022 during Winter Storm Elliott.


Our analysis did not address wind or precipitation, nor did we analyze for a storm with lower temperatures. It is expected that cold weather events will continue to occur and potentially worsen in the future. Based on this expectation, it appears unlikely that EOP-012-1 will prevent a recurrence of generator freezing in conditions similar to or worse than Winter Storm Uri. A full analysis using data available to NERC and FERC should be performed to help guide the improvements to EOP-012 that will provide the desired reliability benefit during future winter storms.

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