Research On IEC 61850 Based Digital Substation Information System And Its Reliability

The implementation of Digital Substation Automation System (DSAS) will greatly reduce the difficulty and cost of information sharing, and will also allow interoperability between Intelligent Electronic Devices (IEDs). These advantages will be helpful to achieve high-performance and low-cost automation system. However, using unified communication standard is the precondition of realization of these advantages. IEC 61850 is the international standards about the network communication system in substations, and its benefits have been proved partly. Furthermore, it has been adopted as an industry standard by many countries including China. As a result, building the information system of DSAS based on IEC 61850 is the best choice.At present, digital substation automation technologies are developing quickly, and IEC 61850 also have been realized partly in some application cases, but there are still several key issues need to be resolved before implementing DSAS and making full use of IEC 61850 advantages. In this paper, DSAS building method, especially the information system building method is studied. Based on it, communication system are studied through simulating method. System reliability evaluating is carried out according to the essence of DSAS. IEC 61850 conformance test is also investigated deeply.First of all, IEC 61850 is not only a communication standard, but also explain the structure and principle of DSAS, so many aspects of building DSAS information system should be related with the intension of IE C61850. In the paper, IEC 61850 is analyzed from the viewpoint of the interoperability objective of it, and its work principle is illustrated. Based on it, the methods of building DSAS information system which can adequately embody interoperability advantage of IEC 61850 is discussed. Data structures are usually used to implement information models in bay level IEDs or process level IEDs. From the interoperability point of view, I propose a logical structure which can reflect information model veritably. A storage structure based on binary tree is also proposed. The use of the two structures can solve the problem of exactitude and high efficiency of information implementation. The determination of networking schemes is important step of building DSAS. The two basic forms of networking schemes, which are separation or merger modes of the process bus and station bus, are discussed. The basic redundancy methods including ring topology, hybrid topology, and fully redundant with double network adapters are discussed too. Transitional scheme of DSAS has to be taken into account since popularization of DSAS will be a long-term course. Thus, the access solutions for traditional switching equipments and traditional bay level IEDs are discussed. As examples, typical DSAS designs for five typical substations are also given.Secondly, networking scheme designs will determine the communication delays, and whether or not the communication delay could meet the requirements would directly impact on whether DSAS functions could be performed successfully. However, much smaller delays means higher cost, so determination of networking scheme suitable for specific substation is critical. Nevertheless, special tool to evaluating the performance of networking schemes is still absent. Therefore, a simulation platform for DSAS networks is built with OPNET Modeler. Models for all typical IEC61850 compatible IEDs are built, and the simulation platform is built based on them. The above five typical DSAS designs are simulated on the platform, and the results have guiding significance.Thirdly, the appropriate evaluating of DSAS reliability is necessary for its application and popularization. However, the special reliability evaluating method for DSAS has not been developed yet. This paper presents a new point view that the essence of DSAS reliability is function reliability. Based on it, a new DSAS reliability model using the graph theory and discrete Markov chain is proposed. In this model, the reliabilities of IED hardware, IED software, and communication system, as well as communication delay are take into account. The calculating method of the transfer matrix is also proposed. According to the transition matrix and the initial state, MTTF can be calculated.The last but not the least, the IEC 61850 conformance testing for IED is a low-cost mean to reduce the risk of non-interoperability, but the methods at present do not work well. Since the requirements from manufacturers and users on the conformance testing are not completely consistent, specific testing program should reflect these requirements both from manufacturers and users. This paper presents the method of the conformance test method. For evaluate IED completely, interoperability testing, performance testing, and functional testing can be also carried out on IEDs. The test methods are proposed in the paper. Based on the analysis of IEC 61850 features, the difficulties and issues need to be resolved for IED tests are presented.