Research On Issues Of Dependability Of Substation Automation System

The smart grid is the upgrade from traditional power grid to the efficient, economical, clean, interactive modern grid, which represents the direction for the future development of the grid. The substation is a key node of the smart grid. Through computer networks, modern communications technology, automatic control and sensing devices, the substation automation system achieves automatic monitoring and control to the substation. To meet the needs of the smart grid substation automation system must be strong and reliable, do a self-diagnosis and recovery to early prevention, early warning, to minimize losses of power down by equipment failure. That is to say substation automation systems is a trusted system, must provide reliable service for grid users, the conception of traditional reliability has been insufficient to describe the nature.Dependable computing based on thinking of fault-tolerant considers that the system must be able to withstand the intrinsic faults, human faults and malicious attacks, emphasize the system’s resistance to the attacks, the ability to identify and resilience, as well as the system’s ability to learn. Dependability’s attributes include reliability, safety, availability, confidentiality, integrity, and maintainability.It is reasonable that dependability is used to describe the characteristics of the substation automation system. But the substation automation system has its own specialty. The conception of dependability must be expanded to meet the demand for to build dependable substation automation systems. In this Dissertation, based on the connotation of dependability and smart grid’s demands, the dependability’s attributes of the substation automation system are analysed in-depth. In order to build dependable substation automation system, issues of protecting system’s dependability including faults preventing, fault tolerance, fault containment and fault prediction are be researched.Because of the open network environment of smart grid, the connotation of dependability is expanded to study the attributes of substation automation systems and threats faced by three aspects from faults, errors and failures. And then we build the dependability model of T1-1substation automation system based on components, research the dependencies among the attributes, verify the reasonableness of the proposed dependability model.Intelligent electronic devices (IED) are the basic units of the substation automation system. The dependability of IEDs is the foundation of dependable substation automation system. Substation automation system based on IEC6185() standard achieves functionalities by the interactions of a number of intelligent electronic devices. A formal design method of IED in substation automation system is proposed. The interactive model of the timed over-current protection IED is described and verified using Timed CSP formal language. At last, Formal description language and stochastic Petri nets are combined to meet the target of system reliability and performance assessment, which give full play the advantages of these two methods. Our methods can guide the software design and interoperability testing experiment for IEDs.However, no matter how perfect the design method is. There are inevitably exist faults in the system. Dependable system must try to avoid potential faults spreading among the system function units. Based on the perspective of theory of complex network, the logical nodes are seen as network’s nodes, the logical connections are seen as network’s edges, complex relationships among logical nodes are expressed with a complex network. The relevant statistic parameters of complex network are calculated. The results show that the interaction relations among logical nodes have the characteristics of small-world and scale-free at the same time. Then the CML based cascading failures of substation automation is established. Simulation results show that the model reveals the propagation of the failure of logical nodes in the system. Finally, the interactive features of the logical nodes in automation system of T1-1substation are analyzed, and the simulations based on the established model further validate the effectiveness of our method.Attacks of certain intensity will be spread in the coupling logical nodes rapidly, eventually lead to a system crash. A cascading failures suppress method based on predictive pinning control is presented. Predictive control and pinning control are used to forecast the states of key nodes in substation automation system. When a node’s state in the current moment is normal, and the next moment in abnormal state, pinning control is implemented for the node to make the subsequent state in normal. And then, Multi-agent technology is employed to realize predictive pinning control by constructing a substation automation system based on multi-agent. Simulations show that the proposed method can effectively suppress the cascade.The information of substation automation system to monitor and control comes from the sensors in the primary equipment. The dependability of the information is the basis to ensure the safe operation of substation automation system and the right decisions of scheduling department. An electronic transformer fault diagnosis method based on wavelet transform is proposed. By a detailed analysis of the fault characteristics of substation electronic transformer, faults are divided into drift deviation, fixed deviation and ratio deviation. The derivatives of the signals are decomposed with bior3.5wavelet. The Lipschitz index of singular point is calculated by modulus maxima. Wavelet energy ratio and mean deviation of the signal are also computed for faults’ diagnosis. Simulations results show that the proposed method can effectively identify the various types of fault signals. The proposed method is integrated in fault diagnosis system of shunt capacitor bank in substation. Now the system is working well in a substation of Guangxi.