Estimating restoration duration

Restoration durations are typically estimated based on the availability of various prime mover types, sizes and numbers. In these estimates it is assumed that load can be picked up as soon as generation becomes available, and the time required for switching operation to energize transformers, energize lines and pickup loads is much less than the time required to make the generation available. In this paper, a case study is presented, supported by a field test, showing that the above assumptions may not necessarily be correct, and restoration duration should be estimated considering both the prime movers timings as well as the switching operations. The paper recommends that the restoration plans should be reviewed and broken down to its restoration levels, tasks and basic operating actions. Operating actions to include: opening/closing breakers, raising/lowering transformer taps, adjusting voltage and frequency set points, starting auxiliary motors, etc. Then, based on operators' experience, the optimistic time, pessimistic time and the most likely time for each action be estimated and assigned. The overall restoration duration then can be estimated using the Critical Path Method, which in turn may dictate revision of the overall restoration plan.