Research On Maintenance And Spare Strategy For Distribution Transformers Considering The Reliability Performance

With the development of smart grids, the traditional equipment management and operation modes cannot satisfy the economy and reliability requirements of both the power companies and the customers. Maintenance startigies and spare analysis of electric power equipments are important issues of power system equipment managements, which is with a fundamental purpose of improving the reliability performance of equipment to reduce the system risk and increasing the economy and reliability of power systems. This thesis discussed the optimization problems of distribution transformer maintenance and shared spare strategies. The main research of this thesis is as follows:To overcome the disadvantage of the previous work that the reliability performance were not considered in maintenance model, this thesis proposed a maintenance scheduling model considering the reliability constraints. Based on the evaluation of transformer heath conditions, the impacts of maintenance mode on the transformer failure rates were discussed. A reliability-based maintenance scheduling optimization model is established by using the sum of planned maintenance cost and outage loss as the objective function, which was solved by using an adaptive real-number-coded genetic algorithm. The annual maintenance plan for transformers can be obtained based on the optimal maintenance time and modes. The proposed technique was applied to optimize the maintenance schedule and evaluate the economy and reliability indices for the RBTS(Roy Billinton Test System) Bus2. In addition, the impacts of reliability constraints on the total system cost is also analyzed.To handle the issues that the previous researches regarding the shared spare strategies of transformers didn’t consider the diversity of load, the Markov model and spare strategy optimization model have been established with consideration of spare mode. Based on the analysis on the transition process and the transition rate of transformers, the reliability Markov model of distribution transformers is established. By solving the state transition function, the probability of each state, the reliability indices of distribution transformers, and the replacement frequency of spare equipment are calculated. Furthermore, taking the sum of the random failure outage loss cost, the investment cost, and the replacement cost as the objective function, the shared spare strategy optimization model is formed. The enumeration method is used to solve the model. Transformers in RBTS Bus2 are used to conduct the numerical study. Spare plans with different spare numbers and strategies of transformers are compared to get the optimal spare plan. Meanwhile, sensitivity analyses on the replacement time and unit power loss are conducted.There is an economical relationship between the maintenance schedule and shared spare strategy, however, few studies take this relationship into account in the maintenance schedule. Based on the economic analysis of the impact of the shared equipment on maintenance schedule, the previous maintenance scheduling model is extended with the addition of investment and replacement cost of shared spare transformers to the objective function, and an improved maintenance scheduling model considering the shared transformers is constituted. Using this new established model, the impact of shared spare strategies, capacity constraint and replacement time on the optimal maintenance schedule are analyzed. Case studies are applied on RBTS Bus2 system. Results show that the spare strategies and capacity constraint of shared spare transformer have a considerable influence on the reliability and economy of transformers maintenance schedule, while the influence of replacement time of shared spare transformers is small.