Modeling Of Information Flow And Reliability Promotion Strategy For Protective Relaying In Smart Substation

The smart substation, which is the trend of substation automation technology, is an important part of smart grid. In recent years, China has carried out a series of practices, which are served as a strong impetus to the development and promotion of this new technology. Different from the conventional protective relaying system, which adopts the integrated mode of “sample-calculation-act”, the protective relaying system of smart substation has greatly improved the information resource sharing and interoperability between devices,which has provided conditions for the advanced protective relaying system. However, the theory and technology supporting system that are suitable for this goal have not been developed yet. Besides, there are still several reliability questions existing in the protective relaying in a smart substation, which restrict the promotion process of smart substation.This paper closely focuses on the engineering application demands of the protective relaying in a smart substation. Aiming at the reliability improvement of the protective relaying in a smart substation and based on the information flow research, a smart substation information flow model, an information flow calculation method, a communication network fault diagnosis method, a whole-view testing method and a reliable synchronization method are proposed in this paper.Major work includes:(1) A smart substation information flow model, including a network connection model, an information flow source model, an information flow sink model and an information flow service model, is constructed in this paper. The information flow model describes the communication relationship between devices, some important characteristics of information flow, message transmission mechanism and coupled relationship of information in a smart substation using graph theory and Network Calculus theory. Information flow model provides the basis for the information flow calculation, communication network fault diagnosis, as well as the whole-view testing method for the protective relaying in a smart substation.(2) Based on the information flow model, an information flow calculation method for the smart substation communication networks is proposed. The distribution of messages, traffic load and the maximum message delay of communication networks can be obtained using the proposed method. Then an abnormal traffic load monitoring method based on the traffic load distribution as well as a sensitivity analysis method based on the maximum message delay distribution is proposed. The information flow calculation method can evaluate the network performance and provide a quantitative basis for the network design and mornitoring. In order to verify the accuracy of the proposed method, a communication network is established in the laboratory. And the distribution of traffic load and maximum message delay calculated using the proposed method is compared to that measured by a network analyzer. Furthermore, possible applications, such as network device selection and network performance analysis are demonstrated based on a 220 kV substation.(3) A message transmission path search algorithm is proposed based on the information flow model. The message transmission path sets up the mapping relationships between a message and devices that the message goes through, which makes it possible for network analyzers to analyze the entire communication network instead of a single message. Based on the message transmission path, a communication network fault diagnosis algorithm is proposed, which can be served as an advanced application of a network analyzer and thus a network analyzer can achieve online communication network fault diagnosis.(4) A whole-view testing method for risk identification of smart substation protective relaying is proposed in this paper. Different from existing methods, the whole-view testing method can test the entire protective relaying system as a whole instead of an individual protection device. Risk points of the smart substation protective relaying system are analysed and several testing methods are proposed to identify and manage the risk points. The whole-view testing device has developed and applied in Guangdong Yunfu Duyang smart substation.(5) A synchronization method based on the compensation of network delay is proposed to achieve the synchronization of network sampling, which does not depend on an external clock. The network delay composition and characteristics are first analyzed. Then a method to swiftly and accurately measure and record the switching delay is proposed, followed by the switch model to achieve the measurement and record of switching delay. A prototype of the switch with the functions of switching delay measurment and record is also developed. Theoretical analysis and testing results show that the proposed method can achieve the synchronization of network sampling effectively, and the reliability of the protective relaying in a smart substation is improved.This research is supported by the National Nature Fundation of China(51577073 and 51377026). Part of the research achievement has won the fisrt prize of science and technology progress of Southern China Power Grid and the third prize of China Electrical Technology. Moreover, part of the achievement of this paper has been applied in the engineering of Southern China Power Grid, which has gained a satisfactory profit for technology and economy, and has verified the accuracy and effectiveness of the methods proposed in this paper.