POWER SYSTEM CONTINGENCY RANKING ADOPTING CONVENTIONAL & FUZZY BASED APPROACH

Abstract

The reliability of power system is generally judged in terms of systems adequacy & security. The term adequacy refers to systems capacity to meet the load demand within the component ratings & voltage limits at any time. The term security refers to system’s ability to withstand the impact of sudden changes due to equipment outage, such as the loss of a generator, transmission line etc. The security of the system is defined in terms of list of contingencies (i.e. transmission line & generator outages) which may cause insecure operation. Clearly as the system conditions changes, this list changes. In order to determine the list of contingencies, load flow analysis should be performed to determine the impact of each contingency on the system performance. However since this is not computationally feasible for on line applications, contingency selection algorithms have been developed to identify the set of contingencies which may create problems. A scalar function called performance index is used in the calculation of the contingency ranking. A real power & voltage performance index is calculated which evaluates the severity of contingency derived from the current overload of lines. The operating state of the power system is a function of time. It keeps on changing due to variation in load level at various buses or due to rescheduling of generation. To keep the system secure, it is imperative to know the impact of unplanned outages in advance so that suitable preventive / control measures can be taken if necessary. In deregulated operating regime - 8 - power system security is an issue that needs due consideration from researchers. Real power & voltage contingency ranking is an integral part of security assessment. The objective of contingency screening & ranking is to quickly & accurately short list critical contingencies from a large list of credible contingencies & rank them according to their severity for further rigorous analysis. A performance index is computed for each single line contingency. To obtain the magnitudes of various parameters a MI power computer aided power system study software which employ iterative methods are used. This document presents an approach using fuzzy logic to evaluate the degree of severity of the considered contingency & to eliminate the masking effect in the Technique. Contingency Ranking considering transmission line & generator outages are tabulated for five bus & IEEE Fourteen bus systems. Then fuzzy logic is developed to unmask the severity between the two conventionally calculated contingency rankings.