  This paper considers state-of-the-art convex relaxations for the AC power
flow equations and introduces new valid cuts based on convex envelopes and
lifted nonlinear constraints. These valid linear inequalities strengthen
existing semidefinite and quadratic programming relaxations and dominate
existing cuts proposed in the litterature. Together with model intersections
and bound tightening, the new linear cuts close 8 of the remaining 16 open test
cases in the NESTA archive for the AC Optimal Power Flow problem.
