Research On Reliability Of Digital Substation Secondary Systems

According to planning of State Grid Corporation, the State Grid Corporation will build or retrofit 6100 smart substations during the period of'National Twelfth Five-Year Plan'. China is becoming the country with most rich experiences on the operation of smart substations in the world. Digital substation is the basic premise and technical means to realize the smart substation. The digital substation failure will lead to large-scale power outage, create lots of loss to the national economy and local residents, and of the social production and life will be greatly affected. Therefore, the reliability of digital substation has important significance to promote the smart substation technology.In this paper, reliability of digital substation secondary systems is studied in-depth and systematically. Firstly, the paper describes the RBD and FTA reliability analysis models. To solve the issues of subjectivity, ambiguity, redundancy and coverage, this paper presents a systematic approach to construct fault trees of digital substations based on the HAZOP method. This method can normatively establish fault trees, and provides a scientific, rational way to identify the inherent or potential risks within the digital substation systems.Second, the paper presents a reliability prediction methods for the new type of digital substation components, and estimates the reliability data of the key components of digital substations. The paper then analyzes the reliability allocation issue of digital substation systems, and proposes an optimization allocation method for engineering applications. Based on the minimum cost allocation method, the paper introduces a feasibility-cost model, and uses the generalized reduced gradient method to find the optimal feasible solution.At last, this paper discusses the maintenance strategy for digital substation system, and proposes an engineering optimization approach for maintenance strategy. Based on reliability analysis, the paper introduces the concept of critical reliability, and uses degree of critical importance to change the parts of the maintenance strategies in order to avoid a large number of condition based maintenance which brings high cost and information channel blockage caused by high volume of data transfer . At the same time, this method can use the minimize cost to improve the system reliability.In order to verify the proposed theory and the methods, several State Grid owned digital substation including J substation, X substation and T substation are examined. The paper compares their reliabilities as well as economy costs. Suggestion on the substation modes are given based on the results of the analysis. The reliability of the X substation, which has the lowest reliability, is enhanced by the proposed reliability allocation method.