An improved voltage-collapse protection algorithm based on local phasors

An improved algorithm to protect against voltage collapse based on two consecutive voltage- and current-phasor measurements to evaluate the voltage stability at a bus is proposed. The change in the apparent-power bus injection during a time interval is exploited for computing the voltage-collapse criterion. The criterion is based on the fact that in the vicinity of the voltage collapse no extra apparent power can be delivered to the affected bus. The one-step algorithm needs no additional checking, irrespective of whether the lines are generating or consuming reactive power.The new algorithm was rigorously tested on different test systems. The results were obtained on a static IEEE 30-bus test system and on the dynamic Belgian–French 32-bus test system that includes full dynamic models of all the power-system components crucial to a voltage-instability analysis. The results show the advantages of the proposed algorithm: it is simple, computationally very fast and easy to implement in a numerical relay.