Quantitative assessments for transient voltage security

Transient voltage security means that the power system is both transient voltage stable and transient voltage dips acceptable. These definitions are clarified in this paper. A self-start technique for computing transient voltage stability related limits is proposed. Based on a margin for transient voltage dip acceptability, a criterion for early termination of the simulation is put forward. Moreover, the procedure of calculating critical clearing time for transient voltage security is extended to that of calculating the critical load level, the minimum reactive power resources and minimum load shedding for keeping transient voltage security. It is also suggested that transient angle stability and transient voltage stability and transient voltage dip acceptability be quantitatively assessed along the same simulation trajectory. The most critical one among the three kinds of limits is regarded as the global transient security limit. The effectiveness and robustness of the proposed approach are demonstrated in this paper with statistic information resulting from 47,987 test cases on two practical power systems