16 May 2012 (Renew Grid)
“The reliability of the bulk power supply in the U.S. remains adequate, according to the North American Electric Reliability Corp.'s (NERC) 2012 State of Reliability report [on ongoing reliability trends]. However, protection-system misoperations remain a significant issue… “There were few changes to the reliability of the bulk power system between 2008 and 2011. The severity risk index (SRI) and the 18 metrics that measure characteristics of adequate level of reliability (ALR) indicate the bulk power system is within the defined acceptable ALR conditions…An improved ALR definition is being developed…From 2008 to 2011, the number of bulk-power-system transmission-related events - excluding events caused by factors other than the performance of the transmission system - resulting in loss of firm load was relatively flat, with an average eight to 10 events per year.”
click to enlarge“The 2011 daily severity risk index value that measures events resulting in the loss of transmission, generation and load showed that the majority of the year's performance was improved compared to 2008, 2009 and 2010…However, when weather-initiated events are included, 2011 had more "high-stress days" (eight days with an SRI greater than five) than had been experienced in prior years (two to five days with an SRI higher than five)… “The availability of the bulk transmission system remains high, with no statistically significant change from 2008 to 2011. The AC circuit availability was above 98%, and the transformer availability was above 96% for both 2010 and 2011…[R]oughly 2% of the events per year (92 events out of 4,185 total events) contained between three and 14 momentary and sustained automatic outages…A recent survey of 133 of these events (from 2008 to 2011) shows that over 60% of the returned survey responses involved abnormal clearing of one or more of the element outages. Nearly half of them involved element outages initiated by protection-system misoperations…”
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