2009 Scenario Reliability Assessment - NERC

Scenario Reliability Self-AssessmentsTransfer Analysis ComparisonFor the subregional transfers, an AC power flow at the transfer test level was conducted with thefirst reported “hard” limit contingency in effect to check for voltage constraints associated withthe transfer. Calculated transfer capabilities are not extrapolated beyond the study transfer testlevels, are non-simultaneous, and based on computer simulations of interconnected electricsystem operations under a specific set of assumed operating conditions for the 2019 Summerpeak season.Each simulation represented a single “snapshot” of the operation of the interconnected systemsbased on the projections of many factors that included expected customer demands, generationdispatch, scheduled maintenance, interconnected transmission network configuration, and theelectric power transfers in effect among the interconnected systems. In real-time operation of theinterconnected electric systems, many of these factors are continuously changing. As a result, theelectric power transfers that can be supported on the transmission systems would vary.Operational IssuesAlthough it is difficult to project actual operational issues from a high level scenario analysissuch as this, a few potential issues come to mind which, while not analyzed here are listed forfuture consideration. Operating guides are likely needed by 2019. The potential differencesbetween the Scenario Case and the Reference Case which would require future evaluationinclude the following:As unit sizes increase with the new capacity additions, requirements for spinningreserve are likely to increase. Operation changes are inevitable.As generation is more concentrated at existing sites, common mode failures andmultiple contingency losses would need to be thoroughly investigated as part of theplanning process under NERC Standards in effect at the time.As more base load generation is added, its capability to follow load would need to beunderstood. At present it is expected that (based on vendor representations) new baseload nuclear plants would have greater load following capability than in the past.Reliability Assessment AnalysisThe reserve margin of the Reference Case in 2019 is 4.1 percent and of the Scenario Case is 9.7percent. Neither would meet the target margin of 15 percent as set out by NERC, however forthis scenario analysis it is instructive to see how we might achieve a better outcome. For a200,000 MW load system with a little less than 2 percent growth per year, we needapproximately 3,000 to 4,000 MW per year to keep pace. At this point in time, the announcedplans in the Reference Case do not, hence deterioration in resource margin over the period. Theamount of resources internal to the Region increase in the Scenario Case. SERC does notperform a system-wide resource adequacy study using probabilistic methods at this time.The amount of resources internal to SERC relied upon to meet state and utility resourcerequirements increases in the Scenario Case. Therefore, the amount of resources external to theRegion being relied on for reliability purposes decreases.2009 Scenario Reliability Assessment Page 141