| With the development of national economy and society, demands to improve reliability of power supply are growing in recent years. Electricity distribution is the final and key stage in the delivery of electricity to end users and it is also the bottleneck of the improvement of the power supply reliability. Statistical analysis of operational data shows that most of Customer Interruptions (CIs) are caused by the distribution network. It draws more and more concern to strengthen the construction of the distribution network. The rise of Smart Grid and Smart Distribution Grid further contribute to the construction of the distribution automation.One of the most import characteristics of the distribution automation is that the remote terminal units of distribution automation (DRTUs) have a great quantity and extensive dispersion, which leads to the high cost of the construction and the maintenance of the distribution automation system. Legacy communication protocols have only defined how bytes are transmitted on the wire. However, they do not specify the meaning (source) of the data and the relationship between the data are unknown. The terminal units do not have self-describing function. How to realize the effective access of large scale of DRTUs and reduce the workload is always a problem which discourages the development of the distribution automation.IEC 61850 is unique. It is a standard for the design of electrical substation automation and has more easily extendable than legacy protocols. This paper establishes an open communication architecture, with the application of IEC61850 and IEC 60870-5-104 standard which is widely used nowadays, trying to solve the communication problem among terminal units and the terminal units to the master station, to finally realize plug and play of the terminal units and reduce the workload of the installation and maintenance. Specific studies include:(1) This paper analyses the application and performance of IP network in distribution automation and draws a conclusion that the IP network can fully meet the requirements of DA. Communication network is the base of the distribution automation, and the use of IP network is predominant for the peer-to-peer communication between terminal units, which can use more standard communication equipments and simplify the construction of distribution automation system. In the distribution automation, layered IP network is used, which is the backbone network and the branch network. The backbone network is used between substations and the control center. The branch network is used between terminal units and substations. The paper analyses the data flow in the backbone and branch network. Simulation results using OPNET show that the packet delivery time is less than 10ms with the use of IP network on base of optical fiber, which is able to meet the requirements of distribution automation. The IP communication network is used in the distribution automation of Guangzhou Power Supply Bureau. The practice proves that the packet delivery time (in the optical fiber channel<1s, in the GPRS channel<2s) meets the requirements.(2) This paper proposes an open communication architecture in distribution automation based on IEC 61850. This paper analyzes and summarizes of the requirements of the communication system in distribution automation, including communication interfaces, communication performance, data refreshing cycle and the scale of the terminal units, and divides the communication system in distribution automation into master station level, circuit level, terminal unit level and process level, puts forward an open communication architecture in distribution automation based on IEC 61850 combined with other communication protocols. The corresponding extension of the configuration language of IEC 61850 and description of the circuit and Ring Main Units are proposed. The communication architecture based on IEC 61850 between the master station and terminal units and among terminal units is also discussed in this paper.(3) This paper expands the IEC 61850 logical node with the application of distribution automation and establishes information models of terminal units. Through analyzing the application of the communication functions in the distribution automation, it is considered that most of the functions can be modeled by the logical nodes in the IEC 61850-7-4. The single phase earth fault line selection and section location in non-effective earthed power system are not defined in IEC 61850. So, the logical nodes of line selection and detection on circuit are built according to several commonly used algorithms. The information models of those intelligent devices such as the FTU for the pole-mounted switch, the FTU for the ring main unit, the TTU for the distribution transformer and the fault-line selection equipment are built by using these logical nodes.(4) Discover/Register model is added for realizing the plug and play of terminal units. Through analyzing the information exchange model of the communication system in the distribution automation, most of the models can be modeled using the ACSI model defined in IEC 61850-7-2. To realize the plug and play of the distribution terminals, Discover/Register model is proposed for the master station discovering new terminal units and for the terminal units registering.(5) The information model and the information exchange model of the communication system in distribution automation are mapped into the standard communication protocol. Discover/Register model is represented by ASN.1 and mapped into the IP network with the use of communication protocol of UDP. The real-time capability of GOOSE model is analyzed, and the mapping of GOOSE using UDP is put forward as well in this paper. Simulation results indicate that the UDP can meet the requirements of the real-time performance in the distribution automation. Mapping to MMS, mapping to Web Services and mapping to IEC60870-5-104 can be used for the core service. This paper emphasizes mapping to Web Services and mapping to IEC 60870-5-104. Mapping to Web Services is suitable for the transmission of information model and mapping to IEC 60870-5-104 is suitable for real-time data transmission. The combination of these two mapping modes is suitable to be applied in the distribution automation.(6) The feasibility of the proposed communication architecture is verified by the testing system. The testing system consists of the Manager machine collecting data in the master station and the FTUs. Manager machine can realize the automatic discovery of terminal units, acquisition of the information model, real-time data acquirement and other functions. Manager is realized by using c++ programming language. FTU model machine can realize registration, information model transmission, real-time data transmission and other functions based on the PZK-3 platform from Kehui Company.Innovations of the paper as follows:(1) The plug and play communication architecture in distribution automation based on IEC 61850 is established in this paper. In this communication architecture, the information model and information exchange model are specified in IEC 61850. Web services are used for transmitting information model and IEC 60870-5-104 for real-time information.(2) Some extensions of the information model are made to meet with distribution automation. The logical nodes of line selection and earth fault location of single phase earth fault in non-effective earthed power system are defined. Based on these logical nodes, the device models of fault line selection and feeder terminal unit (FTU) are defined.(3) Discover/Register model is built to realize the plug and play of the distribution terminals. Discover is used for interrogation terminal units and terminal units report information of themselves by using Register message.The communication architecture proposed by this paper provides uniform information exchange for distribution automation. It will utilize information model and information exchange model of terminal units, and enable one to exchange information with master station independently of a vendor. This will greatly enhance the flexibility and adaptability of terminal units, speeding progress toward the realization of the Smart Grid concept. |
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