Energy function applied to voltage stability studies - Discussion on low voltage solutions with the help of tangent vector

Two main topics regarding the energy function approach for voltage stability analysis are addressed in this paper. First, the problem of the critical low voltage solution identification is discussed. For this sake, the ability of the tangent vector method to correctly identify the low voltage solution that ultimately coalesce with the power system operating solution is investigated. It is shown that the methodology is consistent with the mechanism of the low voltage solutions. Second, the definition of the group of buses related to the weak area of a system is addressed. It is shown that the combined use of the low voltage solution methodology and the tangent vector technique yields good results. Tests were carried out in the IEEE-30, IEEE-57 and IEEE-118 bus test systems.