A new concept of protection against voltage collapse based on local phasors

Voltage instability is strongly influenced by unsuitable allocation or insufficient production of reactive power. It is basically a dynamic phenomenon, but system-oriented approaches are mostly used for the analysis. These approaches are time consuming and therefore not appropriate for on-line monitoring. There is also no clear path to the physical interpretation of the process. Since the phenomenon is of local nature, the goal of this research was to derive a simple method that would yield a voltage collapse proximity indicator with physical meaning. The paper presents a new scheme for protection against voltage collapse based on local phasors. Detection of critical lines instead of critical nodes is used. The difference between apparent power flows at the receiving and the sending end of the line is used for computation of voltage collapse indicator. According to the developed protection scheme, the relay sends a triggering signal to reactive power sources to increase reactive power production. Because of the computational simplicity the proposed protection scheme can be used for on-line system monitoring as well as for off-line analyses.