Incorporation of dynamic voltage stability constraints in the ATC determination of power system

The evaluation of available transfer capability (ATC) in deregulated power system should take into account thermal limits, transient, steady-state and dynamic angle stability as well as the voltage stability limits. The consideration of voltage stability in the determination of ATC, however, was usually neglected. On the other hand, under the power market environment, voltage instability becomes a more important consideration in many countries in recent years, especially when following a large disturbance in a heavily stressed power system over long distances. To satisfy the increasing need of updating and posting the ATC values at regular intervals, on-line voltage stability assessment with acceptable accuracy is required. Classified along the time-scale, the voltage stability of a system may be split into two categories of the short-term and long-term dynamics. In this paper, short-term dynamics is assumed to be satisfied in a stable way, which is common in most practical cases. Quasi-steady-state (QSS) approximation of long-term dynamics is introduced to evaluate ATC with dynamic voltage stability constraints. A new ATC determination scheme using QSS approximation is proposed in this paper and implemented on a test system. The performance of the QSS approximation is also compared with the full-time-scale simulation. From the results, it shows that the proposed scheme can evaluate ATC with dynamic voltage stability constraints at acceptable accuracy, while the calculation speed is accelerated considerably to meet the real-time requirement.