Verifying Distribution Networks for Secure Restoration by Enumerating All Critical Failures

If several feeders are cut in a severe accident, distribution networks should be restored by reconfiguring switches automatically with smart grid technologies. Although there have been several restoration algorithms developed to find the new network configuration, they might fail to restore the whole network if the cut critically damaged the network. The networks design has to guarantee that it is restorable under any possible cut for secure power delivery, but it is computationally hard task to examine all possible cuts in a large-scale network with complex electrical constraints. This paper presents a novel method to find all the critical (unrestorable) cuts with great efficiency to verify the network design. Our method first runs a fast screening algorithm based on hitting set enumeration; the algorithm selects suspicious cuts without naively examining all possible cuts. Next, unrestorable cuts are identified from the suspicious ones with another algorithm, which strictly tests the restorability of the network under each suspicious cut without redundantly repeating heavy power flow calculations. Thorough experiments on two distribution networks reveal that our method can find thousands of unrestorable cuts from the trillions of possible cuts in a large 432-bus network with no significant false negatives. This is the first work to reveal the vulnerability of a large-scale distribution network extensively.