Investigation of the voltage stability region involving on-load tap changers

A new approach for estimating the voltage stability region of power systems is presented in this paper. This voltage stability region is conservative because it is based on ten sufficient conditions. The power flow solutions are utilized to estimate the voltage stability region of the taps of on-load tap changers (OLTCs), voltage magnitudes, and phase angles. The coupling relation between the real and reactive powers is taken into account. The computation time is reasonable because only matrix and vector computation is involved. Two practical power systems were employed in demonstrating the capability of the proposed approach. The test results confirm that it is applicable to large power systems.