Power System Transient Stability Detection Based on Characteristic Concave or Convex of Traj ectory

With the application of APMU (angle & phase measurement unit) based on GPS (global position system) in power system, online system transient instability detection becomes feasible. It is of great significance to transient stability emergent control that out-of-step condition is as soon as possible detected. This paper is concerned with faster transient instability detection for online application. A supposition is strictly proved in phase portrait, and an improved instability detection method is presented, which is independent of the network structure, system parameters and model because of using observation data. During the process of proof, damping coefficient is considered in system model to keep it more reasonable. According to the geometric characteristics of system trajectory, a new index Deltak is defined and used to identify system transient stability. The simulation results show that the detection theory of transient instability is correct, and the improved index is more effective than the pre-used method. Since the index is reliable and requires less computational time, it can be applied to the design of out-of-step relaying