Reliability And Security Study Of The Digital Substation System

With the continuous development of power grid and the deep going reform of electricity market, the requirements for the safe and economic operation of power grid and power quality are continuous increased. Substation as an important node in the grid, more and more information is supplied for the dispatching center, which is not only the conventional operation and accident information, but also the status monitoring information of important devices. And at the same time more and more complex control functions need to be implemented. Thus the substation must be digitalized, informationized and prompt information modeling. Therefore, digital substation automation system is the development trend of substation automation system in the future.Compared to the traditional substation automation system (SAS), digital substation automation system (DSAS) has a series of significant advantages. But as a new system, there are still many problems in DSAS at this stage, such as reliability and security. Over the years, domestic and foreign scholars on the reliability of SAS had done a lot of research. But with new features, the traditional method has been less suitable for DSAS. Therefore, it is of great significance for establishing the reliability model of DSAS with new analytical methods. In addition, the dependence of DSAS on communications technology is far higher than the SAS, thus the accompanying information security risks can not be ignored. The existing majority methods on safety analysis of Substation system remain the qualitative analysis, or the technical analysis. It is of little significance for the guidance of actual safety management. Therefore, the search for a comprehensive quantitative and enforceable safety analysis method is significant for the safe operation of DSAS.Firstly, the characteristics, function, and architecture of the DSAS are overviewed, and the research status quo of reliability and safety on DSAS at this stage is introduced. Then based on the focus of power business users on the reliability, the concept of function reliability and structure reliability are proposed.For the analysis of function reliability, an analytical method is proposed in this paper, based on a function of DSAS. It is different from the conventional analytical methods based on a system or devices. The analytical goal is to analyze the sustainable effective time of the function other than the system's or devices', and it could avoid the shortcomings of the traditional analysis that the reliability indices are too general to give more effective information. To the characteristics of function reliability analysis, GO Principle is adopted in this paper. First the law of GO principle is introduced. Then a digital transmission line protection is taken for example, and its GO function reliability model is established. Based on the model, the sustainable and effective time of the protection function is computed, and the weak links is analyzed. At last the effective of this method used in function reliability analysis is stated.For the analysis of structural reliability, directing at the dependence of DSAS on communications networks, an analysis method on the structure reliability of network is introduced in this paper. First parallel redundant protocol (PRP) set in the IEC62439 standard and its future prospects are introduced. Then a bus station control layer in the T2-type transmission substation defined in IEC61850 standard is taken for example and the use of PRP network is assumed. Its structure reliability model is constructed under Bayesian network analysis method. Then the weak links of its network structure is analyzed by diagnostic reasoning. Finally, the method is compared with the fault tree analysis to prove its superiority.Finally, for the risk analysis on information security of DSAS, the ISO13335 Information Security risk model and risk factor identification method about the risk factors are described in this article, and an index system of risk assessment based on the security factors is established. On this basis, the three measures of the risk factors (probability, impact, non-controlling) are evaluated fuzzily under the integrated use of fuzzy theory and AHP Group Decision. For the validity of the results given by experts, a method combined with the information entropy theory is proposed in this paper, and an index of validity coefficients is defined for the correction of the assessment results.