A SECURITY BASED APPROACH TO COMPOSITE POWER SYSTEM RELIABILITY EVALUATION
Khan, M. D. Easin
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There is considerable interest in the application of probability methods to composite system reliability evaluation. The problem is extremely complex because of the need to include detailed modelling of both generation and transmission facilities and to consider multiple levels of component failures. Quantitative adequacy assessment of a composite power system is generally done using a contingency enumeration approach which includes the evaluation of contingencies, the classification of these contingencies according to selected failure criteria and the accumulation of adequacy indices. There are several network solution methods presently available depending upon the failure criteria and the intent behind the studies. In this thesis, adequacy indices are calculated using three methods, namely network flow, dc and ac load flow and the importance of utilizing an ac load flow method in composite system reliability analysis is clearly illustrated. The computation time increases tremendously when an ac load flow method is used specifically for a large system where the inclusion of higher level outages cannot be ignored in the calculation of representative indices. In order to reduce the computation time when using ac load flow without sacrificing much accuracy, different approximate methods can be utilized. Adequacy indices are calculated and presented in this thesis using three ranking methods and a new technique designated as the selection method. The CPU times and the accuracy of the methods as compared to the reference values obtained with an exhaustive ac load flow solution are discussed. The presently available techniques for quantitative reliability evaluation of composite power systems are in the adequacy domain. The most significant quantitative indices in this regard are those which relate to load curtailments and many utilities have concerns in interpreting the expected load curtailment indices. A framework for incorporating the steady-state security considerations in the reliability evaluation of composite power systems is examined and extended in this thesis. The system operating states are quantified using the contingency enumeration method for three different constraint sets. The indices are also calculated by combining the contingency enumeration method and a Monte Carlo simulation approach through the use of hybrid methods to quantify the various system operating states and the results are compared with the analytical values. This thesis presents a new risk index designated as the Composite System Operating State Risk (CSOSR). This index is defined and its utilization in system expansion and unit commitment in composite generation and transmission systems is illustrated. The concepts presented in this thesis are illustrated numerically using two basic test systems.