On voltage collapse and apparent-power losses

The paper proposes a new concept for assessing vulnerably of a power system in terms of voltage stability. The concept is based on the apparent-power losses and uses only local data, i.e. voltage and current phasors at every line end in the system. In the paper, we prove that, at the voltage-collapse point, the entire increase in loading of the most critical line is due to increased transmission losses, which also coincides with the singularity of the Jacobian matrix. It is shown that this information can be used as an indication of a voltage-instability proximity. The proposed local method has several advantages over the existing static and dynamic methods, which is also shown in the paper.