With the comprehensive rollout of urban and rural power grid transformation projects across the country, distribution network automation has been gradually implemented in various regions. Distribution line automation is the foundation and an important component of distribution network automation. Localities can, based on their specific circumstances, start with key areas within the distribution network, optimize the network structure, and implement the system in stages. First, automate the transformation of some distribution lines, and finally cover the entire network, establishing a high-level distribution network automation system to improve power quality and reliability. This paper proposes corresponding automation schemes for distribution lines in urban 10 kV distribution networks and analyzes the actual operation mode of multi-source, multi-circuit ring power supply systems. [b]1 Design Objectives[/b] The planning and design principle of the distribution network automation system is to first achieve comprehensive management of distribution lines. Specific objectives include optimizing the distribution line structure and wiring methods, rationally segmenting the network, and rationally selecting line automation switches, communication equipment, and master station DMS software; achieving flexible connection of distribution lines, eliminating transient faults, isolating permanent faults, reducing the scope of planned maintenance and outages, reducing maintenance and outage time, improving the reliability of power supply and the level of distribution network operation and management, and reducing line maintenance workload and operating costs. Specific functions include equipment positioning and management, operation management, accident prediction and fault diagnosis, fault isolation and transfer, local line tracking and dynamic coloring, and temporary network modification. [b]2 System Structure[/b] The power distribution line automation system consists of a master station DMS system, a communication system, and equipment line automation switches. 2.1 Master Station DMS The master station DMS software includes SCADA, AM/FM/GIS, automatic fault isolation and transfer system, and advanced application software. The system adopts an open platform with a flexible and convenient graphical interface, allowing for vertical and horizontal integration. SCADA enables remote measurement, remote signaling, remote control, alarm, monitoring, operation simulation, data recording and analysis of power distribution lines, and has corresponding functions supported by GIS. Automatic Map (AM), Equipment Management (FM), and Geographic Information System (GIS) can map the digitized power supply area and the geographical location of power distribution line equipment one-to-one with the parameters and operating status of the power equipment, realizing the geographicization of power distribution line information, visualization and real-time operation data, facilitating the operation and management of power distribution lines. The automatic fault isolation and transfer system can quickly identify the faulty section after a fault, isolate the faulty area, and automatically generate a load transfer power supply plan based on the system's operating status, restoring normal power supply to the non-faulty sections of the distribution line. Advanced application software can perform power flow calculations, short-circuit current calculations, network reconstruction and outage scheme analysis, and switch operation topology identification and coloring. The basic hardware configuration of the master station DMS includes a PC industrial control computer, a fiber optic modem and communication ports, as well as input/output devices (large-screen color display, printer, etc.). 2.2 Communication System The communication system adopts a master-slave, dual-ring fiber optic communication method, which has well-known advantages. The dual-fiber ring structure retains the advantage of saving fiber optic cable in the ring structure and overcomes the disadvantage of any point fault in the fiber optic cable affecting system operation, possessing self-healing capabilities. The entire communication system includes a master station modem and several slave modems configured with FTUs. Each modem has two pairs of fiber optic transceiver ports, connected in series by two fibers to form a dual-fiber communication ring (master ring and slave ring). Under normal circumstances, both rings operate, and signals are transmitted simultaneously in opposite directions within the two rings. If any optical cable or fiber optic modem in the loop fails, the optical signal will automatically return from the fiber optic modems on either side of the fault point to the other loop, ensuring normal communication operation. The communication protocol used is DNP3.0, which is suitable for distribution networks, but other communication protocols can also be used depending on the actual situation. 2.3 Line Automation Switches Line automation switches can consider using reclosers, automatic distribution switches (automatic reclosing sectionalizers), or pole-mounted SF6 switches and vacuum switches with corresponding control systems. Based on the characteristics of each distribution network and fully considering the future development of the distribution network and the upgrade capabilities of the equipment, pole-mounted SF6 switches or pole-mounted vacuum switches are preferable. This is because both types of switches have the ability to interrupt short-circuit currents, and the line switch itself can complete the interruption function for faulty sections at this level, reducing the chance of line outages; moreover, these two types of switches have a long operating history and certain operating experience. Line switches are equipped with FTUs to form line automation switches. FTUs can be network controlled and have remote communication interfaces, enabling telemetry, remote signaling, and remote control. They support multiple communication methods, various power measurements, load and switch action count recording, and provide programming interfaces and interface software, etc. Information required by the distribution line automation system is collected by each FTU and uploaded to the master station via the communication system. Control commands from the master station are then issued to each FTU for execution via the communication system. In addition, FTUs can automatically monitor switch wear and report to the master station when necessary. Dispatchers can then arrange maintenance plans based on this information, avoiding blind maintenance, reducing planned maintenance time, and narrowing the scope of planned maintenance. [b]3 Operation Mode Analysis[/b] During normal operation of the distribution line, the FTUs of the line automation switches continuously monitor and record switch status, line current, voltage, etc., and calculate operating parameters such as power factor, active power, and reactive power. When abnormalities occur in switch status or line parameters, the FTUs report the abnormal information to the master station via the communication system. The main station DMS system polls the FTUs (Fault Transfer Units) on the line at regular intervals, updating the real-time database with the queried information and eventually storing it in the historical database. Dispatchers can query this data on the electrical equipment location map displayed on the main station's large screen, which is set against a regional map background. They can also directly remotely control the switches on each line and change the system's operating mode. When a fault occurs in a distribution line, the main station DMS system receives fault information from an FTU or substation circuit breaker, activates the fault detection, isolation, and load transfer system, and issues an alarm. It then checks the event records and other information of the relevant FTUs, automatically determines the fault isolation and non-faulty section load transfer schemes, performs simulation verification, and finally requests the dispatcher to remotely operate the system or for the main station DMS system to implement the scheme automatically. The system operation mode is illustrated below using the multi-source, multi-circuit power supply method shown in Figure 1 as an example. [img=300,134]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hbdljs-3/54-11.jpg[/img] Under normal conditions, the interconnecting switches a, b, c, and d between the distribution lines are all open, and the four lines operate independently. The FTU (Functional Unit) of each switch on the line monitors, calculates, and stores analog electrical parameters such as current and voltage, as well as status parameters such as contact opening and closing positions. The main station DMS (Distributed Management System) automatically queries the FTU, refreshes and stores the main station database, and the dispatcher can also directly query or remotely operate the system at any time. In the event of a fault, if it is a transient fault, the corresponding outgoing circuit breaker or line automation switch will open and then reclose to eliminate the fault and restore power supply to the line. If the transient fault point is on section II of line A, switch e will open and then reclose; if the fault point is on section I, outgoing circuit breaker 1 will open and then reclose. If a permanent fault occurs on line A, the outgoing circuit breaker will trip and lock out, causing a power outage on line A. All switches on this line will quickly report the abnormality to the main station, initiating fault detection, isolation, and load transfer procedures. The faulty section (assumed to be section I) will be determined, and the main station system will automatically or manually implement fault isolation operations. Line switch e will be disconnected to isolate the faulty section (section I), and then a load transfer scheme for the non-faulty section (section II) will be determined. The system will first select line B as the transfer power source and perform a load transfer simulation verification. If the verification scheme is successful, the system will provide the switch action sequence, allowing the dispatcher to remotely operate or the main station DMS to automatically operate the corresponding switches to implement the transfer scheme. If the verification shows that line B cannot carry the load of the non-faulty section (section II), the system will then sequentially select other lines for verification until the final transfer scheme is determined and successfully implemented. [b]4 Conclusion[/b] This power distribution line automation scheme is applicable to power distribution lines with various power supply methods. It can automatically isolate faulty lines and automatically restore power supply to non-faulty sections, greatly improving the power supply reliability and operation automation of power distribution lines. The open platform of the main station system is compatible with other advanced application software and can be integrated vertically and horizontally to realize the communication interface with the upper-level system and support the substation integrated automation system. The FTU's switch wear monitoring function provides a basis for reasonably arranging maintenance plans. If a fault location system is added, the fault branch and fault point can be located in a very short time after the fault. It can not only eliminate permanent faults, but also eliminate the fault hazards reflected by transient faults, ensuring the safe operation of power distribution lines. [b]References[/b] ［1］ Lin Gongping. Power distribution network feeder automation technology and its application. Automation of Electric Power Systems, 1998, (4). ［2］ Cai Guilong, Jin Xiaoda. Communication scheme setting of power distribution automation system. Power System Technology, 1999, (4). ［3］ Xu Layuan. Selection Guide for Distribution Network Automation Equipment. Beijing: China Water Resources and Hydropower Press, 1997.