Fast Reassessment of Prolonged Electricity Shortages under Shared Fuel Interruptions

Résumé : When several generators share a fuel supply, one interruption can disable them together and cause electricity shortages lasting days. Such interruptions can be made less frequent, for example by weatherizing gas supply, or shorter, for example by on-site backup fuel. Yet traditional resource adequacy indices, expected unserved energy and loss-of-load hours, fail to distinguish such measures whenever they remove the same expected time without fuel, because for interruptions independent of system conditions these indices depend on the interruptions only through this time. Their difference is revealed by prolonged-shortage exposure, the expected annual hours in shortages of at least a given duration, whose exact chronological calculation must be repeated for every interruption scenario. To reduce this cost, a fast reassessment method with guaranteed accuracy is proposed. Network calculations are performed once and condensed into a restoration response, the additional prolonged-shortage hours caused by one interruption of each duration, from which any scenario is evaluated as a weighted sum without new simulation. An hour-by-hour error bound determines whether this evaluation is accurate enough, and exact dynamic programming is applied otherwise, so that every result lies within a requested tolerance of the exact value on the same Monte Carlo samples. On the Reliability Test System of the Grid Modernization Laboratory Consortium, most evaluations were accepted, fully accepted scenarios typically ran more than 200 times faster than exact calculation, and total computation time decreased in every workload. Measures against fuel interruptions can thus be screened quickly and accurately by their effect on prolonged shortages.