PERFORMANCE EVALUATION OF POWER SYSTEM COMPONENTS USING FAULT TREE ANALYSIS

Abstract

Due to ever increasing electrical energy demand, the world has become fully dependent on electrical power systems. This instigates mandatory requirement of high reliability of power system operation. The present study discusses the performance evaluation of a power system generating plant, namely 330MW combined cycle Pragati power plant and power transformers. For the purpose of failure analysis of a power system, failure information is a necessity. For the purpose of calculation of failure probability, fault tree analysis is used. Fault Tree Analysis is a well-documented representation of the system failure logic, in which a top-down tree is built, with top event representing the unit failure. However, uncertainty may arise due to partial information about the problem, due to source of information which is not fully reliable, due to inherent precision in the language with which the problem is defined, or multiple sources of information conflicting with each other. The past failure information results in short term failure probability which does not provide reliable information about the future behavior of the system. Therefore, conventional fault tree analysis integrated with expert based fuzzy set theory has been used for the failure analysis of the two systems. In expert fuzzy analysis, expert opinion is considered in the form of triangular and trapezoidal fuzzy numbers and then applied in fault tree for evaluation of system failure probability. The expert opinions are judged on the basis of decision making under uncertainty using Laplace and Hurwicz criterion. For the power plant, based on the number of occurrence of failures and total repair time, mean time to repair (MTTR), mean time between failures (MTBF), mean time to failure (MTTF),, failure rate, probability of occurrence has been estimated. As the components/subsystems present in the plant are repairable, system availability/unavailability is calculated. In case of power transformers, the failure probability, of the power transformers is calculated and by using the concept of Fuzzy importance index (FII) the failure events are ranked according to their sensitivity towards the transformer failure. This will help the decision maker to prioritize the components for repair and attention so as to improve the reliability of the system.