Architecture And New Applications Of Real-Time Ethernet Based Digital Substations

With the rapid development of Ethernet and the advent of the IEC 61850 standard, the new generation of digital substations characterized by digital process level has drawn high attention in recent years. If all the substation devices are connected with one unified communication network and the information is exchanged in the same network, the substation architecture can be greatly simplified to enhance the flexibility and scalability. Moreover, on the basis of open architecture and information sharing, a lot of new functions and applications will be developed to improve the performance of substation automation system. Therefore, the architecture and several new applications in digital substation based on real-time Ethernet are chosen to be the research topics of the thesis, including substation architecture design, Intelligent Electronic Device (IED) software system design, protective relay testing, protective relay fault-tolerance, and dynamic redundancy of protective relay. The outputs of the thesis are listed as follows.Taking practical 220kV and 500kV substation as examples, the process level architectures are designed using cascade star topology. Destination address identification and Virtual Local Area Network (VLAN) identification are used to multicast Sampled Analog Value (SAV) messages and Generic Object Oriented Substation Event (GOOSE) messages. Simulation results in OPNET show that the process bus is suitable to transmit SAV and GOOSE messages in the shared network if the network bandwidth and switch capability are sufficient and the different messages are scheduled according to priority tap. Furthermore, the multicast communication is capable to reduce the network load.On the basis of modeling the information traffic and analysis of traffic characteristic, a traffic control approach based on Leaky Bucket is proposed. The parameters of the Leaky Bucket in IEDs and switches are discussed. Simulations show that the burst traffic can be smoothed to low-speed traffic using the proposed method. Therefore, the burst traffic and broadcast storm can be restrained and the message loss due to buffer overflow of switch can be prevented.The application of generic hardware platforms and component based software technology has the potential to enhance the flexibility of substation IEDs. The component model is proposed to specify various software components with appropriate granularity and provide a framework to integrate them efficiently. The component model is established by extension of IEC 61850 information model using the concept of IEC 61499. The function-related data, detailed function algorithms, and execution logic of the algorithms are contained in the proposed component model, which inherits the IEC 61850 information model. Considerable merits of the proposed IED design approach are also discussed. The prototype system in MATLAB/Simulink demonstrates the feasibility of the proposed component model.The protective relay testing system can be simplified due to the integrative information transmission in the shared network. A transient testing method using a standalone Personal Computer (PC) without commercial test device is proposed. All the test tasks including transient data generation, SAV/GOOSE messages transmission/capture, and performance analysis, are implemented on a standalone PC. Moreover, a WinPcap based communication module residing in the PC is developed to transmit and capture numerous SAV/GOOSE messages instead of multiple Ethernet ports of a commercial test device. Precalculated post-fault current and voltage is utilized to perform a close-loop test to evaluate the reclosure capability. Experiment results demonstrate the effectiveness of the proposed solution for functional test of protective relays.Two fault-tolerant methods are proposed to prevent protective relays from mis-operating in digital substation due to fake measurement: information fusion of sampled value from various Instrument Transformers (IT) and information fusion of start-up signals from various protection IEDs. The former method takes advantage of redundant sampled valve from various ITs to deduce the status of power system and provide supplementary information to protective relay to make a correct decision. Simulations demonstrate the effectiveness of the proposed method. Moreover, the ITs providing fake measurement can also be identified. The later method is an improved one, which utilizes the start-up signals from various protection IEDs to indicate the power system status by means of voting.Finally, after the analysis of reconfigurability of digital substation IED communication and software architecture, the approach of dynamic redundancy of protective relay based on on-line IED reconfiguration is proposed, as well as its procedure. The application prospect and disadvantages of the method are also discussed. The proposed approach is feasible to enhance the reliability of protection system in a cost-efficiency way in low and medium voltage power systems. For high voltage power system, dual configuration of protection system is still recommended. However, the proposed approach can be adopted to ensure the primary equipment is always under protection of dual protective relays to guarantee the reliability.