Introduction With the rapid development of the national economy and the power industry, the requirements for the automation and informatization level of the power system are also increasing. The power system consists of five parts: power generation, transmission, substation, distribution, and users. Currently, integrated power automation combines modern electronic technology, communication technology, computer technology, network technology, and graphics technology with system equipment, organically integrating the monitoring, protection, control, and management of the power system under normal and fault conditions with the work management of power supply enterprises. 1. Substation Integrated Automation As a crucial basic link in the power grid, the level of automation in the substation system directly affects the safe and stable operation of the power grid. Substation integrated automation systems have experienced rapid development and widespread application, becoming an important benchmark for measuring the automation level of power enterprises. The electrical equipment in a substation is generally divided into primary equipment and secondary equipment. Primary equipment refers to distribution devices and power transformers with different voltages. Secondary equipment is auxiliary electrical equipment built upon the primary equipment, including four main modules: relay protection and automatic devices, instrumentation and measurement control, local monitoring, and remote control. Secondary equipment monitors, measures, and controls primary equipment, ensuring the safe, reliable, and economical operation of substation electrical equipment. Substation automation systems are an important component of power grid dispatch automation and also an independent system, collecting and recording a large amount of equipment operating data to provide reliable data for substation equipment maintenance. 1.1 Substation Structure Currently, there are three structural forms in substation integrated automation systems: centralized, centralized-distributed, and decentralized-distributed. Decentralized-distributed structures are the trend in the development of substation integrated automation. Logically, substation automation systems can be divided into two layers: the substation layer (station-level measurement and control units) and the bay layer (bay units). Alternatively, they can be divided into three layers: the substation layer, the communication layer, and the bay layer. The main characteristic of this system is that it is designed according to the components of the substation, specifically the circuit breaker bays. All data acquisition, protection, and control functions required for a single circuit breaker bay are centralized and completed by one or several intelligent measurement and control units. These measurement and control units can be placed directly on the circuit breaker cabinet or installed near the circuit breaker bay, connected to each other by optical fiber or special communication cables. This system represents the trend of modern substation automation technology development, significantly reducing connecting cables, reducing electromagnetic interference in cable transmission, and possessing high reliability. It effectively prevents some faults from affecting others, facilitating maintenance and expansion. 1.2 The measurement and control unit in the distributed architecture of the RTU unit, also known as a remote terminal unit (RTU), is the equipment used in substations to measure and monitor power parameters and equipment operating conditions. RTUs are widely used in automated monitoring systems, undertaking the "upload and download" of various remote information. They are crucial equipment for substations to achieve remote data acquisition and monitoring, and are key to realizing comprehensive automation of substations and the power system. Data communication between the data collected by the RTU from the field and the monitoring signals sent by the control center is an indispensable part of the substation automation system. Data communication not only enables information exchange between subsystems or functional blocks within the integrated automation system but also completes the communication tasks between the substation and the entire power system. Substation automation data communication must possess the following characteristics: reliability (strong anti-interference capability, ensuring that the failure of any node (measurement and control unit, RTU, etc.) does not affect the entire control network); openness (compatible with other external devices, suitable for different communication media and protocol requirements); and real-time performance (real-time information transmission). 1.3 Communication Mechanisms Currently, computer technology, multimedia technology, network technology, and fieldbus technology are developing rapidly, comprehensively improving data communication performance. There are currently two communication mechanisms: POLLING communication and CSMA/CD communication. POLLING topology can be either a star network or a bus network, represented by RS-485. CSMA/CD topology is generally a bus network, represented by LonWorks. 2 Fieldbus Overview Fieldbus is a fully digital, bidirectional, multi-station communication system connecting intelligent field devices and automation systems. It primarily solves the problems of digital communication between intelligent instruments, controllers, actuators, and other field devices in industrial settings, as well as information transmission between these field control devices and higher-level control systems. Fieldbus plays a crucial role in the integrated automation of power systems. Currently, there are approximately forty types of fieldbuses, the most commonly used being Siemens' ProfiBus, Echelon's LonWorks, and Bosch's CAN, among others. Based on the characteristics of substations, the selected fieldbus should possess features such as flexible topology, convenient wiring, reliable communication, good real-time performance, and strong error correction capabilities. LonWorks is one such powerful fieldbus. 3. Application of LonWorks in Substations 3.1 LonWorks Bus LonWorks is a comprehensive, fully open, and interoperable distributed control network technology developed by Echelon Systems, Inc. in the United States. Due to its high reliability, openness, and low cost, LonWorks control network technology has been adopted by numerous manufacturers and users in their control network solutions. More than 2,500 companies worldwide utilize LonWorks technology to produce a wide variety of LonWorks products to meet the distributed control network requirements of modern buildings, factories, transportation systems, urban infrastructure (water, electricity, gas, etc.), and home automation systems. The core of LonWorks is the neural network chip and the LonTalk protocol. Neuron chips are the hardware foundation for implementing the LonTalk protocol and the key to realizing LonWorks networks. Currently, the application of fieldbus in substation integrated automation mainly involves the transformation of remote control units, network structure, and communication. Compared with other fieldbuses, especially with traditional control schemes such as DCS and PLC, LonWorks has obvious advantages: (1) One-to-many structure. LonWorks technology simplifies wiring, shortens construction cycle, greatly reduces installation costs, and reduces maintenance. Furthermore, new equipment does not require re-laying cables, greatly saving manpower, material resources, and financial resources. (2) All-digital signals. In traditional control technology, signal transmission is 1-5V or 4-20mA. In LonWorks technology, signal transmission is all-digital, and the reliable LonTalk protocol is used, making data transmission reliable, fast, and with strong anti-interference capabilities. (3) LonWorks has openness and good interoperability. Users can choose various products from different manufacturers and integrate them to form a control scheme with the required control functions. 3.2 Application of LonWorks in RTUs Traditional RTUs convert various electrical parameters into standardized electrical signals through their respective transmitters, enabling YC telemetry, direct input of switch contacts into the RTU's switching channels for YX telesignaling, and connection of switch contact signals from the RTU to the substation control circuit for YK remote control. To achieve a hierarchical distributed structure, a fieldbus must be introduced. LonWorks' Neurochip has three CPUs, enabling pipelined processing; its 11 I/O ports can be flexibly configured to interface with peripheral devices. The RTU modified using the Neurochip, in addition to performing the original telemetry, telesignaling, and remote control functions, also performs tasks such as packaging field information and parameter data, flow processing, and error handling, making the RTU a LonWorks node connected to the LonWorks network for remote and distributed monitoring and control. 3.3 Application of LonWorks Communication Network in Substation Integrated Automation Substation communication network structures include three types: star, ring, and bus. Star topologies lead to the presence of a central station, which becomes a reliability bottleneck; its failure can paralyze the entire network. Ring topologies suffer from data path interruptions due to the failure of one node. Bus networks offer advantages such as flexible expansion, simplicity, and reliability, making them particularly suitable for substation communication networks with high reliability requirements. LonWorks buses are suitable for various network structures, and the bus topology is currently the most widely used. LonWorks' powerful scalability has been proven in large-scale building automation systems abroad. The choice of communication media is also crucial for substation integrated automation systems. Common media include fiber optic cables and twisted-pair cables. Fiber optic cables offer excellent interference resistance but are point-to-point, resulting in waste and complex installation and maintenance. Twisted-pair cables, on the other hand, allow for flexible expansion based on the network structure. The LonTalk protocol of the LonWorks fieldbus defines various communication media, including twisted-pair, power lines, radio frequency, infrared, coaxial cables, and fiber optics, with twisted-pair cables being the most commonly used. The use of twisted-pair cables can reduce the cost of substation integrated automation cabling. The LonTalk protocol provides information management functions, defining four basic message service types: acknowledged, request/response, unacknowledged repeat, and unacknowledged; it supports the priority predictable P-persistent CSMA/CD conflict algorithm; and it supports acknowledgement services. LonWorks fieldbus supports the substation communication mechanism CSMA/CD, and the LonTalk protocol uses priority predictable P-persistent CSMA/CD, enabling the network to achieve maximum communication even under overload conditions. This effectively prevents network congestion and signal/parameter loss due to excessive signal parameters, greatly improving the reliability of data transmission in the communication network. 4. Summary The pace of substation integrated automation is constantly advancing. The level of substation integrated automation will improve with the development of fieldbus technology, computer technology, and network technology. The application of fieldbus in integrated automation systems is becoming increasingly common, especially LonWorks distributed control network technology, which achieves true distributed control. This improves control flexibility and reduces the risks caused by system instability. LonWorks fieldbus's flexible network structure, powerful neural network chips, and LonTalk protocol greatly improve the reliability of control and communication, and its integration with substation integrated automation systems is becoming increasingly close.