A measurement-based VSI for voltage dependent loads using angle difference between tangent lines of load and PV curves

In this short communication, a generic measurement-based voltage stability indicator (VSI) is presented with voltage dependent load models incorporated. It uses the angle difference between the tangent lines of the load characteristic curve and the PV curve. Based on the Thevenin equivalent estimated from the measurements, the proposed VSI can be easily applied to both the ZIP and the exponential load models. Time domain simulation results on both load models demonstrate that the proposed VSI accurately indicates voltage instability and outperforms a conventional VSI which is based on a constant power load model.