Abstract: Based on the background of the power distribution automation system project of Baifengling Tunnel on the Yongjin Expressway, this paper analyzes in detail the design concept, system composition, functional modules, and system design of the power distribution automation system of the expressway tunnel using industrial Ethernet. The power distribution automation system of the Yongjin Expressway tunnel was developed on the INT-SCADA platform. Practice shows that the system operates well. Keywords: Industrial Ethernet; Expressway; Monitoring system. The power distribution automation system of the expressway tunnel is an important component of expressway construction. The Baifengling Tunnel project of the Yongjin Expressway consists of two tunnels, left and right. The left tunnel is 1974m long, and the right tunnel is 1540m long. The planned power distribution capacity of the entire tunnel is 1500KVA, divided into two substations, east and west. The western substation is a 10KV power distribution system and a 10/0.4KV substation, while the eastern substation is a 10/0.4KV substation. Each substation serves as a substation of the tunnel power distribution automation system. The specific wiring diagram of the substation system is shown in Figure 1. Each substation is designed as an unmanned station. The monitoring system includes a measurement and control unit, a serial port hub, and an industrial Ethernet switch. Figure 1 shows the wiring diagram of the Baifengling Tunnel power supply system. The main design objectives of the highway tunnel power distribution automation system are: to provide relay protection for 10KV electrical equipment, online monitoring of operating conditions, local/remote control operation of various controllable switches, load switching, automatic start-up of the generator system and economic optimization of the power distribution system, control interlocking/linkage suitable for various operating modes, and information sharing through communication network connections. Since the total length of the tunnel is approximately 1900m and the entire power distribution automation system has many parameters, fieldbus technology cannot meet the system requirements. Industrial Ethernet protocol is universal, has a fast transmission speed, and has been widely used; therefore, industrial Ethernet technology is adopted to implement the highway tunnel power distribution automation system. 1. Composition of the Tunnel Power Distribution Automation System The entire tunnel power distribution automation system adopts a modular and networked, layered, distributed, and open system structure that combines industrial Ethernet and fieldbus. Ethernet is the most successful local area network technology to date, boasting advantages such as high transmission speed, low cost, easy installation, and good compatibility. It is also one of the most widely used information network technologies. Industrial Ethernet applies Ethernet technology to the control field, integrating the upper-layer information network with the lower-layer control network. Ethernet uses a switching method for data transmission. Data from multiple devices can be centralized at a network switch and communicate with the monitoring center through a single upload channel, reducing communication equipment, significantly lowering system costs, simplifying system structure, and facilitating post-maintenance. Monitoring equipment can be connected to the system through a network switch without the need for additional communication equipment, making system expansion convenient and flexible. Based on the principle of distributed control and centralized monitoring, the system is divided into intervals, modular design, and distributed processing to achieve a solution of device layering and network layering. The entire system is divided into a field-level control layer, a substation-level control layer, a network management layer, and a master station-level control layer from bottom to top. The system structure is shown in Figure 2. 1.1 Field-level Control Layer The monitoring units in the field-level control layer are required to operate stably and reliably, be easy to maintain, and meet the automation design requirements of the project. This solution selects the PA100, PA200, and IDM20 series integrated digital relay measurement and control devices from Nanjing Intal Electric Co., Ltd. These devices are connected to a serial hub and a front-end industrial control computer at the substation level via MODBUS fieldbus. Other intelligent devices, such as transformer temperature controllers, diesel generator controllers, and UPS controllers, are also connected to the front-end industrial control computer, forming an organically coordinated integrated automation system for a single 10/0.4kV substation. 1.2 Substation Level Control Layer The substation level control layer is crucial for field control. The hardware uses a reliable Advantech industrial control computer, the system software uses a Microsoft Windows 2000 multi-tasking, multi-threaded operating system, and the application software uses INT-SCADA integrated monitoring system software. The system can realize functions such as telemetry, remote signaling, remote control, remote adjustment, alarm display, data storage, statistical reporting, and substation optimized operation control. The monitoring computer at the substation level control layer has complete access and control capabilities for various intelligent devices at the field level control layer, while also possessing strong operational hierarchy, allowing for different password restrictions and different operators to modify different objects. Even if the entire network fails, the industrial control computer at the substation level can still control and operate the system at its own level. Substations do not interfere with each other, ensuring the independent, safe, and reliable operation of the system. 1.3 Network Management The Baifengling Tunnel on the Yongjin Expressway is long and has a complex power system. Using fieldbus technology would be insufficient to meet the requirements of real-time performance, security, and reliability. Therefore, fiber optic dual-redundant industrial Ethernet technology is adopted at the network layer. The industrial Ethernet switch used is the Dongtu Telecom-KIEN2000 industrial Ethernet switch, which has two uplink redundant 100Mbps fiber optic ports. Utilizing the uplink redundancy, a self-healing ring network can be formed, improving system reliability. Six ordinary 10/100Mbps twisted-pair ports have adaptive functionality; each port can automatically set to 10BASE-TX or 100BASE-TX status and full-duplex or half-duplex operating mode. This device can be connected via plug-and-play, saving startup time. 24V power redundancy is provided, enhancing the reliability of the network and system. 1.4 Master Station Level Control Layer Project Due to the long distance between the tunnel substation and the monitoring center, a master/slave communication method is adopted, with a four-core single-mode fiber optic connection. The field control layer is used as a slave station, and the main monitoring center as the master station. The master and slave stations communicate via industrial Ethernet. The main monitoring center uses a redundant configuration of two servers, with the monitoring units being ordinary industrial control computers. The operating system software is Microsoft Windows 2000, and the monitoring software is INT-SCADA software. Power data collected by the slave station front-end monitoring units is sent to the master station via fiber optic industrial Ethernet. The communication management unit of the master station is DE-334. Since there are two slave stations in this tunnel group system, the monitoring host also needs to have a communication server HUB. In the master station control system, the main monitoring unit connects to the communication server, and the communication server connects to the communication manager via TCP/IP protocol. Due to the long distance between the monitoring host and the slave station control units, each slave station control unit is designed to communicate with the host via fiber optic cable, using the TCP/IP communication protocol. The monitoring host can collect data from each substation control unit to achieve remote control, remote signaling, and remote measurement functions for each substation's field control layer. 2. Monitoring System Functional Module Design This solution implements protection, remote measurement, remote signaling, remote control, and remote adjustment for the primary main equipment of the power distribution system, and remote control and management for secondary and auxiliary equipment, achieving comprehensive management. All measurement and control devices within the power distribution system use microcomputer-based equipment, which, together with the microcomputer monitoring system through a communication network, constitute the entire integrated automation system. 2.1 Data Acquisition Acquired signals include AC voltage, current, active power, reactive power, frequency, power factor, DC input analog quantities, and digital quantities, and have the function of calculating integrated energy consumption. The system can collect circuit breaker positions, handcart positions, grounding switch positions, etc., display the status locally, and upload the data to the host and dispatch terminal, with switch position change signals being transmitted first. 2.2 Control Function Receives and executes remote control commands and performs feedback verification. Various switches and circuit breakers can be remotely controlled by simulating a handheld switch via a computer. 2.3 Human-Machine Interface (HMI) The SCADA system boasts powerful HMI design capabilities, allowing for the creation of various user interfaces, such as primary system diagrams, system structure diagrams, virtual instrument panels, central signal panels, centralized operation panels, panel layout diagrams, geographic information maps, inspection route diagrams, secondary schematic diagrams, secondary wiring diagrams, various curves, bar graphs, and control information displays. Any information that the INT-SCADA system can collect can be displayed on configurable images, and related control operations can be performed locally (see Figure 3). 2.4 Event Recording Data acquisition is accurate and reliable, and the system possesses fault signal display, fault analysis and event recall, and data query functions. It can also retain alarm events (see Figure 4). 2.5 Alarm Functions The alarm functions are comprehensive and accurate, providing feedback in audible and visual forms. Alarm signals can be manually and remotely reset. Alarms include switch and circuit breaker position change alarms, current and voltage measurement over-limit alarms, SCADA system fault alarms, protection action alarms, and grounding signal alarms. 2.6 Reporting and Printing Functions: Various reports and curves can be generated as required. Various graphs, reports, and curves can be printed by hour, day, month, and year. 2.7 Communication Functions: Communication mode conforms to the TCP/IP protocol of the Internet network. 3. Development and Implementation of the Tunnel Power Distribution Automation System: SCADA (Supervisory Control and Data Acquisition) systems, as one of the most effective computer hardware and software systems for automating production processes and business management, encompass two meanings: one is a distributed data acquisition system, i.e., an intelligent data acquisition system, commonly referred to as a lower-level machine; the other is a data processing and display system, i.e., a central upper-level machine system. The INT-SCADA integrated monitoring system software based on Microsoft Windows 2000 is located at the station-level control layer of the system. The monitoring configuration platform is a large-scale application software based on the system platform. It integrates control technology, human-machine interface technology, database technology, and network and communication technology, enabling control system developers to complete the construction of control system functions and the detection of the operating status of field equipment without relying on a specific computer language. This greatly facilitates control system designers. 4 Conclusion Based on the background of the power system project of the Yongjin Expressway tunnel, this paper analyzes in detail the power distribution automation system of the expressway tunnel based on industrial Ethernet and its implementation method. The system structure adopts a hierarchical and distributed network bus approach and uses microcomputer monitoring to realize the functions of "remote signaling, remote measurement and remote control", ensuring the safety and reliability of power supply and providing users with a direct, simple and effective operation method for real-time management and monitoring. Since the opening of the Yongjin Expressway on December 28, 2005, the entire power distribution automation system has been operating normally and has certain reference value for the design of similar projects. [b]References:[/b][1] Zhuang Yajun, et al. Design and application of Ethernet monitoring system[J]. Microcomputer Information, 2005, (4). [2] Jiang Fan. Function of power monitoring system of expressway tunnel[J]. Highway, 2002, (supplement). [3] Wang Mingnian, He Linsheng. Computer system of intelligent monitoring center for tunnel[J]. Highway Transportation Technology, 2001, (2). [4] Song Yinghua. 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