Fast algorithm for voltage collapse protection based on local phasors

Voltage collapse is basically a dynamic phenomenon with rather slow dynamics. Therefore mostly static methods based on the system Jacobian matrix were proposed for its analysis. Because of computational burden these methods are slow and not appropriate for estimating the proximity of power system to voltage collapse in real time. In the paper a new algorithm for protection against voltage collapse based on local phasors is proposed. The algorithm is based on the difference between apparent power flows on both ends of each line in the system. Critical lines in the system are identified by means of the proposed scheme. Because of its computational simplicity the proposed algorithm is very fast and therefore applicable in on-line protection schemes. The proposed method was tested on various test systems including 275-bus Slovenian test system. The proposed algorithm can be easily implemented in a numerical relay. The proposed method may be also introduced as an additional tool in the power system voltage security assessment as well as in the planning of remedial actions for emergency system states.