  The optimal power flow problem is central to many tasks in the design and
operation of electric power grids. This problem seeks the minimum cost
operating point for an electric power grid while satisfying both engineering
requirements and physical laws describing how power flows through the electric
network. By additionally considering the possibility of component failures and
using an accurate AC power flow model of the electric network, the
security-constrained AC optimal power flow (SC-AC-OPF) problem is of paramount
practical relevance. To assess recent progress in solution algorithms for
SC-AC-OPF problems and spur new innovations, the U.S. Department of Energy's
Advanced Research Projects Agency--Energy (ARPA-E) organized Challenge 1 of the
Grid Optimization (GO) competition. This paper describes the SC-AC-OPF problem
formulation used in the competition, overviews historical developments and the
state of the art in SC-AC-OPF algorithms, discusses the competition, and
summarizes the algorithms used by the top three teams in Challenge 1 of the GO
Competition (Teams gollnlp, GO-SNIP, and GMI-GO).
