  Linear approximations of the AC power flow equations are of great
significance for the computational efficiency of large-scale optimal power flow
(OPF) problems. Put differently, the feasibility of the obtained solution is
essential for practical use cases of OPF. However, most studies focus on
approximation error and come short of comprehensively studying the AC
feasibility of different linear approximations of power flow. This paper
discusses the merits of widely-used linear approximations of active power in
OPF problems. The advantages and disadvantages of the linearized models are
discussed with respect to four criteria; accuracy of the linear approximation,
optimality, feasibility, and computation time. Each method is tested on five
different systems.
