  Modern power systems face a grand challenge in grid management due to
increased electricity demand, imminent disturbances, and uncertainties
associated with renewable generation, which can compromise grid security. The
security assessment is directly connected to the robustness of the operating
condition and is evaluated by analyzing proximity to the power flow solution
space's boundary. Calculating location of such a boundary is a computationally
challenging task, linked to the power flow equations' non-linear nature,
presence of technological constraints, and complicated network topology. In
this paper we introduce a general framework to characterize points on the power
flow solution space boundary in terms of auxiliary variables subject to
algebraic constraints. Then we develop an adaptive continuation algorithm to
trace 1-dimensional sections of boundary curves which exhibits robust
performance and computational tractability. Implementation of the algorithm is
described in detail, and its performance is validated on different test
networks.
