Abstract—The AC optimal power flow (AC OPF) problem is considered and five convex relaxations for solving this problem—the semidefinite, chordal, conic, and moment-based ones as well as the QC relaxation—are overviewed. The specifics of the AC formulation and also the nonconvexity of the problem are described in detail. Each of the relaxations for OPF is written in explicit form. The semidefinite, chordal and conic relaxations are of major interest. They are implemented on a test example of four nodes.