Study On The Delay-non-determinism Of Ethernet-based Substation Automation System

Substation secondary systems play an important role in ensuring the security, stable and economic operation on primary systems. The rapid development of the electric power system, the constraining of environment and the introduction of competition power market converge press on the secondary system for function integrating, information sharing and resource utilizing, which have a higher network, integration and automation requisite on the secondary system. The Ethernet-based substation automation system (ESAS) brings a new idea and innovation. But the Ethernet-based integrated information transmission results in the problem of delay-non-determinism, which has become the kernel factor that may influence on the safety and stability of ESAS and must be resolved before applications. So this dissertation devoted to the research on this problem, in which the three aspects of the idea of the new ESAS, the delay-non-determinism analysis and proposal are researched systematically. Considering that the traditional ESAS with object-oriented design has the inadequacy of flexibility, open and maintainability, the new ESAS with network-oriented design has been created, in which the standardization of software and hardware platform is applied to develop the universal intelligent devices; the functions is reconfigured through network and centralized upwards, the information sharing is accomplished through two-layer flat structure and information integrated transmission network. The design idea, implementation methods and merit of the new ESAS are described. Some important problems are emphasized and some solutions to the pivotal problems of the system are also discussed in detail. In the aspect of delay-non-determinism analysis, considering that it is argued that ESAS exists delay-non-deterministic problem, several factors that bring about the problem of delay-non-determinism are discussed in this paper and OPNET network simulator software is employed to verify the delay-non-determinism behavior in the different factors. The method to quantitatively analyze the impact of delay-non-determinism on the functional safety for distributed interlock is proposed, achieving accurate forecasting of the safety. In the aspect of delay-non-determinism process, this paper proposes a method based on queuing theory for determining buffer size of station main unit (SMU) in the network for station-level on emergency, in which the buffer size is given in advance on the basis of meeting the requirement of message loss probability and delay, improving the delay-determinism of information transmission in SMU. To solve the delay-non-deterministic problem of the network for process-level, the method in the end-nodes based on the priority-tag is proposed, and the implementation scheme method through introducing a prioritization mechanism into the protocol stacks is presented, overcoming effectively the problem of flow collision of the integrative information transmission and improving the delay-determinism of information transmission in the end-nodes. The method based on leaky bucket and classification of service mechanism to overcome the delay-non-deterministic problem of the internetworking for whole-station is proposed, in which the leaky bucket model is established and the formulation of the upper delay of various information flows is derived through introducing network calculus theory. The formulas above can be used to verify whether the delay of each information flow meets constraint. To overcome the delay-non-deterministic problem of the network for the information integrated transmission between substation and control center, the method of concrete implementation based on the differentiated services network is proposed, solving effectively the problem of flow collision in limited network resources and keep each message traffic's delay constraint even in case of network congestion, and providing improvement in delay-determinism.