Protection against voltage collapse based on local phasors

Since the phenomenon of voltage collapse is of a local nature, the goal of this research was to derive a simple method that would yield a voltage collapse proximity indicator with physical meaning. Therefore a new scheme for protection against voltage collapse based on local phasors is proposed. Detection of critical lines instead of critical nodes is used. The difference between apparent power flows on 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.