Improved tangent hyperplane method for transient stability studies [of power systems]

The tangent hyperplane method is a technique for estimating critical clearing times in transient stability studies. It has a similar aim to Lyapunov type methods, in that an approximation is made of the boundary of the region of stability in the state space thus avoiding the need to integrate the equations of the post fault system. The method involves the calculation of hyperplanes tangent to the stability boundary at certain unstable singular points. When the method was first described, it was found that, although it was simple in concept and easy to apply, good accuracy was not always achieved. The authors describe a way to estimate the reliability of the method for a given fault. This increases the value of the method significantly, since it is known when the result can be accepted and when an alternative method need be employed. Tests on a 10 machine, 39-bus system are described