Comparative Study of Voltage Security Indices in Terms of Limit-Induced Bifurcation Effect

This paper compares six types of major voltage security indices (VSIs) in terms of limit-induced bifurcation (LIB) effect. The compared VSIs are the voltage collapse proximity indicator (VCPI), L-index, L
_mn
-index, minimum singular value (MSV), tangent vector index (TVI), and optimal-power-flow-based direct method (OPF-DM). These VSIs are evaluated on the WSCC 9-bus system in different voltage collapse conditions, where LIB or saddle-node bifurcation (SNB) determines the voltage collapse point (VCP). The evaluation results show that most of the VSIs basically overestimate the voltage security if LIB occurs. Only the OPF-DM with the complementarity constraint evaluates the appropriate voltage security even if LIB occurs.