A predictive out of step protection scheme based on PMU enabled dynamic state estimation

This paper presents a predictive energy based Out of Step Protection scheme. It is based on real time dynamic monitoring of the system achieved through the implementation of a distributed, substation based dynamic state estimator. The estimator utilizes only local measurements and requires PMU synchronized measurements; additional measurements from non-GPS synchronized relays are also utilized and increase the redundancy of the system. The dynamic state estimator provides the evolution of the dynamic state of the system (real time dynamic model) at rates of 60 times per second. The real time dynamic model of the system is then utilized to evaluate the system´s energy function based on Lyapunov´s direct method and extract stability properties from the energy function. Comparison of the proposed approach to conventional Out of Step protection schemes (based on impedance relays) is demonstrated through illustrative examples. The proposed method detects out of step conditions much earlier than conventional methods.