Dynamic Gradient Method for PEBS Detection in Power System Transient Stability Assessment

Jeffrey T. Scruggs Lamine Mili The Bradley Department of Electrical and Computer Engineering Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0111 Abstract – In methods for assessing the critical clearing time based on the transient energy function, the dominant procedures in use for detecting the exit point across the Potential Energy Boundary Surface (PEBS) are the ray and the gradient methods. Because both methods rely on the geometrical characteristics of the post-fault potential energy surface, they may yield erroneous results. In this paper, a more reliable method for PEBS detection is proposed. It is called the dynamic gradient method to indicate that from a given system state, a small portion of the trajectory of the gradient system is approximated and tested for convergence toward the postfault stable equilibrium point. It is shown that a trade-off between computing time and reliability can be found as the number of machines in the system becomes greater. The method is illustrated on 3-machine and 10-machine systems.