Daily Security Analysis on the EDF Power Transmission System Based on a Hierarchized State Estimation Procedure

Abstract This paper describes the daily A.C. security analysis system developped after the black out of December 19, 1978, in order to realistically simulate, a day in advance, the most critical state of the power system. After having recalled the objectives and then the three step organization which was set up : photograph of the power system, extrapolation and simulation, the important role played by the state estimation function is shown. Some remarks about the specific environment of the daily predictive data processing system highlight the originality of the choices retained for the implementation of a decentralized and hierarchized state estimation procedure. The first phase of the process for obtaining the photograph of the system consists in performing, in parallel, state estimation on the power sub-systems of each and every area control center. In the paper, this is shown to be valid. Using figures from an EDF experiment, the practical interest of this approach is explained both from the processing point of view and with regards to the efficiency of the localisation and detection of errors. In order to make further load flow simulations possible,'a complete coherent system state is necessary and, for this, a second phase is carried out where the national control center performs the state estimation process on the complete network taken as a whole. These computations may reveal measurement errors, previously concealed by the zone partitioning, which must be corrected. At the same time, the state estimation process is extended to external neighbouring systems in order to establish corresponding hypotheses which are necessary for the later load flow simulations.