A systematic approach to setting underfrequency relays in electric power systems /

Generation loss contingencies in electric power systems result in a deviation of system frequency from nominal, a condition which must be corrected promptly in order to prevent further degradation of the power system. Automatic load-shedding using underfrequency relays is one of the techniques used to correct abnormal frequency deviations and prevent the risk of uncontrolled outages. If sufficient load is shed following a contingency to preserve interconnections and keep generators on-line, the system can be restored with relative speed and ease. On the other hand, if a declining frequency condition is not dealt with adequately, a cascading disconnection of generating units may develop, leading to a possible total system blackout.This thesis develops and tests a new systematic method for setting underfrequency relays offering a number of advantages over conventional methods. A discretized swing equation model is used to evaluate the system frequency following a contingency, and the operational logic of an underfrequency relay is modeled using mixed integer linear programming (MILP) techniques. The proposed approach computes relay settings with respect to a subset of all plausible contingencies for a given system. A method for selecting the subset of contingencies for inclusion in the MILP is presented. The goal of this thesis is to demonstrate that given certain types of degrees of freedom in the relay setting problem, it is possible to obtain a set of relay settings that limits damage or disconnection of generating units for each and every possible generation loss outage in a given system, while attempting to shed the least amount of load for each contingency