Study Of Power System Operational Reliability Analysis And Evaluation

With the development of science and technology, improvement of the living standards of the people and the characteristics of the power system, power network has been expanding. This enlarges the range of the power system accidents, which has been catching more and more spotlights about the reliability of the power system.The operation of power system has random characteristics for the volatile of user's load demand and random failures of the element in the system, and power industry deregulation and fast-growing renewable generating capacity results in more highly stressed and unpredictable operating conditions. Deterministic approach can not satisfy the needs of modern power system. To make a decision must be taken into account operation scenes as much as possible, integrated all of the probability of occurrence of each scene and its consequences, and in ensure the risk of whole power system can be managed to an acceptable level.After decades of research and practice, it is already quite mature that the application and study of the reliability concepts and evaluation indices based on probabilities, reliability computational model, accumulation and statistic of component reliability parameters, through combination of basic reliability engineering principles and practical situation, mathematical model of power system. Because of calculation methods and complexity of power system, there have some conflict between the calculation speed and accuracy of the Power System Reliability Analysis and Risk Assessment, and there are many matters in the concept and engineering practice of element's importance, it must be more develop and completed. Especially in operation environment, a quick approach for power system reliability analysis and risk assessment was required, to obtain the current reliability state and forecast the developing trend of the power system with enough accuracy, in a finite time. In this thesis, a theoretical study of power system reliability analysis and risk assessment in operation environment is carried out. The main works and innovative achievements of the thesis are as follows:(1) In traditional substation scheme reliability analysis, the effects of fault clearance and fault restoration are not elaborately investigated. In this thesis, a novel methodology for the substation scheme reliability analysis is proposed. In which, the effects of both fault clearance and fault restoration are considered. The proposed method is on the basis of non-sequential Monte Carlo simulation and topology analysis. First, cut set of breakers surrounding the failed elements is found to simulate fault clearance, meanwhile the influence of protection and breaker failure is considered. Then, all non-failed switchgears are closed and cut set of switchgears surrounding the failed elements is found to simulate fault restoration. Unsatisfied load demand of two processes is calculated respectively, which can get more reasonable result. Compared with the traditional model considered before, the computation complexity is reduced and the accuracy is enhanced in the proposed method. The proposed method is applied for a study case and the necessity and effectiveness is demonstrated.(2) This thesis presents a Monte Carlo simulation method for reliability analysis of generalized power network which integrates impedance components, such as transmission lines and transformers, and non-impedance components, such as breakers and switches. First, topology analysis for sub station was carried out to get equivalent nodes and the connectedness between these nodes and impedance components. Second, system topology analysis was carried out to get the equivalent network which is used to calculate the measure indicatrix on reliability of power network. During the simulation procedure for generalized power network, a quickly local topology analysis technology based on same transitive closure of incidence matrix was proposed to save computation resources. Test system shows that the proposed method was more practical.(3) The Monte Carlo Simulation Approach used in reliability analysis of the power system requires vast computing resource due to low convergence speed. Aiming to solve this problem, a fast power system reliability analyzing model based on Markov chain is founded from view of operation, by assuming that equipments'fault rate has exponential distribution characteristics. first, a criterion to sort the power system running state into3states which can be easy implemented, as well as corresponding state space transition expression, are proposed; second, based on the historical running data or simulation data, the Markov transition probability matrix of the power system is formed. By using the transition probability matrix and initial distribution, power system reliability indices including state transition probability, steady state probability and the mean time to first failure can be fast analyzed, thus quick reliability assessment of power system can be realized. The example testified the Markov property of the power system state transition and the effectiveness of this research.(4) Weak parts of a power system can be recognized using sensitivity analysis, which has been an important technique for system reliability assessment and enhancement. Aiming at inadequacy of conventional sensitivity analysis, an improved algorithm of improvement potential component importance analysis is founded to make it be fit for actual demands better, and efficiently avoid calculating error of reliability indices affecting results of component importance analysis. Using this algorithm in the generalized power network reliability analysis, this thesis evaluates and compares importance of primary equipments directly to satisfy the need for maintenance strategy better.