Modeling and analysis of transient stability of power systems with special emphasis on the effect of protective relaying

This dissertation deals with the problem of modeling and analysing in the slow time scale of the power system during transients produced by major disturbances (faults). The problem is addressed with special emphasis on the protective system.;The system is modeled by (1) a set of non-linear differential and algebraic equations representing the power system and its control elements; (2) a set of non-linear differential and algebraic equations for the protective system; and (3) a set of algebraic relations to represent the link between these two subsystems. The equations for the power system and its control are not developed in detail, since they are standardized. The equations for the protective system are based on the phasor domain design principles of commonly used relays. It is of special interest that the relay settings appear directly in the equations. The inputs to the protective system are selected state variables of the power system model (voltage and current phasors) and the binary outputs are the circuit breaker positions. The link between the two subsystems is modeled by explicit formulation of the nodal admittance matrix as a function of the circuit breaker positions. The complete model characteristics can be summarized as deterministic, non-linear, high-order and discontinuous.;The model itself demonstrates the strong dependency of power systems transient stability with fault and relay related factors. The complete model was implemented in a computer program to study some specific situations in a hypothetical power system. Given the complexity of the system, simplifications were made in order to analyze some protection related problems. Specifically, the determination of the limits for the relay settings based on the preservation of transient stability. This analysis led to the definition of the relay setting stability region and the protection success region. The dissertation concludes with a short inquiry into the application of these definitions and analysis to the emerging field of adaptive relaying, where the problem is stated as an optimisation problem.