Large-scale power exchanges over long distance through high/ultra-high voltage AC/DC transmission systems increase the probability of sudden loss of bulk power in the receiving-end power systems. To prevent such accident from deteriorating the security

an emergency load shedding mathematical model and an efficient trajectory sensitivity based algorithm are proposed

which consider both the transient security of power system and the economics of load shedding. The model

whose objective is to minimize the total load shedding cost

includes constraints on transient voltage security

transient frequency security and the load to be shed. Transient voltage and frequency security is accurately assessed based on the time-domain trajectory. As such a model is a large-scale nonlinear programming problem with time-domain parameter constraints incapable of direct solution

the security constraints are linearized by trajectory sensitivity for solution as a linear programming. The consistency of the solution is guaranteed by iteration

the validity of the algorithm tested and verified through a provincial power system.