  The convex restriction of the power flow feasible sets identifies the convex
subset of power injections where the solution for power flow is guaranteed to
exist and satisfy the operational constraints. In contrast to convex
relaxations, the convex restriction provides a sufficient condition for power
flow feasibility and is particularly useful for problems involving uncertainty
in the power generation and demand. In this paper, we present a general
framework of constructing convex restriction of an algebraic set defined by
equality and inequality constraints and apply the framework to power flow
feasibility problem. The procedure results in convex quadratic constraints that
provide a sufficiently large region for practical operation of the grid.
