[align=left] A substation is an electromagnetic energy conversion and redistribution unit. Many protection devices, detection devices, and auxiliary devices in a power system are designed for the entire substation. Therefore, the substation is a crucial link in the power transmission and distribution system and a major control point of the power grid. With the increase in voltage levels and power grid complexity, as well as the increase in power supply radius and transmission and distribution capacity, the use of traditional primary and secondary equipment in substations is increasingly unable to meet the requirements of reducing substation costs and improving the safety and reliability of substation operation. To meet these requirements, it is necessary to vigorously develop and promote integrated substation automation systems. The Concept and Benefits of Integrated Substation Automation Systems 1.1 Concept An integrated substation automation system is a comprehensive automation device for secondary equipment in a power system that integrates protection, measurement, control, and remote transmission functions. It adopts microcomputer and network technologies and fully utilizes the advantages of digital communication to achieve data sharing. Substation automation encompasses: the acquisition of electrical quantities and the monitoring, control, and regulation of the status of electrical equipment (such as circuit breakers), enabling monitoring and operation during normal substation operation to ensure its normal operation and safety; in the event of an accident, the acquisition, monitoring, and control of transient electrical quantities (achieved through relay protection, fault recording, etc.) to quickly isolate the fault, and the restoration of normal substation operation after the accident. From a long-term perspective, it should also include monitoring information of the high-voltage electrical equipment itself (such as insulation and status monitoring of circuit breakers, transformers, surge arresters, etc.). Besides transmitting substation information to the dispatch center, operation department, and relay protection engineers, it also needs to be transmitted to the maintenance and repair center to provide raw data for the development of electrical equipment monitoring and maintenance plans. In summary, the integrated substation automation system will impact at least three aspects: unmanned substation operation, the practical application of power grid dispatch automation systems, and the reliability of power supply. It involves various specialties and departments within power supply companies, including the operation devices, engineering, and technology of secondary systems such as automation, remote control, communication, relay protection, measurement, and metering, and even places new demands on primary equipment. Meanwhile, it also involves various departments including substation maintenance, operation, and dispatch, and extensively involves planning, design, standardization, quality inspection, manufacturers, management systems, and other related departments and issues. It is a comprehensive and complex system engineering project, and a comprehensive application of modern technology and management in power enterprises. 1.2 Benefits 1.2.1 Reduce the cost of substation projects. [b]The main approaches are:[/b] a) Adopting object-oriented distributed design, replacing a large number of point-to-point long-distance signal cables with a communication network composed of a very small number of communication cables, and replacing or simplifying secondary hardware interlocking circuits with software interlocking, saving a large amount of cables and corresponding construction and commissioning work. b) Due to the adoption of a distributed structure, the traditional large control room design can be eliminated, saving land and building area. c) The distributed structure and communication network make the future expansion of the integrated automation system very convenient and simple, without requiring much modification to the original system, making full use of the original technical equipment, and saving investment when expanding the system. d) The modular software of the integrated automation system allows the supplier's software configuration to handle the traditionally complex point-to-point commissioning work. This enables on-site infrastructure construction and factory acceptance to proceed in parallel, accelerating the overall project progress. 1.2.2 Improving the safety and reliability of substation operation [b]The main approaches are:[/b] a) Microcomputer-based protection units are frequently in online self-test mode (including temperature monitoring), immediately alarming upon any abnormality, unlike traditional protection devices which are only calibrated a few times a year, and their actual operation is only known after a fault. b) Traditional protection devices generally provide only one set of settings, while microcomputer-based protection units can provide multiple sets of settings, allowing remote selection when the operating mode changes, and providing the possibility of modifying settings during dynamic processes. c) Microcomputer-based protection units can more easily implement functions such as single-phase grounding line selection, fault location, and fault recording in low-current grounding systems. d) After fault handling, the integrated automation system can restore the substation to its pre-accident state. e) The integrated automation system applies many advanced technologies, improving operational reliability. For example, FACTS technology has greatly improved the dynamic performance of power systems, significantly increasing the transmission capacity of power lines and improving the stability of power systems; GPS technology, applied to dynamic detection and control, has enabled previously impossible control and measurement accuracy, as well as fault analysis, device testing, and the acquisition of special parameters. [b]2 Fieldbus Technology[/b] 2.1 Introduction Fieldbus is an interconnected communication network that has developed rapidly in various automation fields in recent years. Its name encompasses two aspects: "field" refers to the connection between devices (the lowest level) in the working environment, and "bus" means that this communication connection must adhere to a unified technical standard, enabling interconnection and interoperability between devices. As a basic communication network between devices, fieldbus must have simple protocols, strong fault tolerance, good security, and low cost. It must also have high real-time performance and be suitable for frequent information exchange, thus differing from upper-level high-speed data communication networks. Currently, fieldbus technology is developing rapidly internationally, resulting in various bus standards, among which Lonworks, CANbus, FFbus, and Profibus are influential and representative. However, a unified international standard has not yet been formed. Fieldbus, with its novel architecture, has brought revolutionary changes to various control systems, and the intelligent electrical networks it forms have demonstrated powerful advantages. Currently, the network topology of fieldbus mostly adopts a bus type. In substation integrated automation systems, fieldbus is a digital, bidirectional, multi-branch communication network connecting intelligent field devices and the automation system. Therefore, it is an integration of field communication networks and control systems, predicated on the use of intelligent electronic devices (IEDs). 2.2 Significance of Integrated Automation Systems In substation integrated automation systems, the physical layer of serial communication between IEDs and between IEDs and the master station initially commonly used RS-232. Subsequently, many devices adopted the higher-performance RS-485 (half-duplex) and RS-422 (full-duplex). At the substation level, some systems use various computer local area networks, such as Novell networks and Ethernet. Although the types of hardware are not numerous, the communication protocols used are very inconsistent. Equipment from different manufacturers generally cannot interconnect or interoperate. Protocol conversion, or gateways, have become the most important devices in the network structure, causing great inconvenience to users. Fieldbus not only has openness and interoperability, but also has the advantages of distributed control functions and high reliability. Therefore, the use of fieldbus in substation integrated automation systems is an inevitable trend. [b]3 Current Status of Substation Integrated Automation Systems at Home and Abroad[/b] 3.1 Foreign Products are represented by ABB's SCS100/200 and Siemens' LSA678. a) Signal acquisition method: Multi-DSP structure is generally adopted at the bay level terminal, integrating protection, waveform recording, metering, and remote control functions, and making signal acquisition completely distributed and decentralized, simplifying the secondary circuit. b) Digital communication method: The communication network mainly uses optical fiber as the medium (such as LSA678). Optical fiber has a high communication rate and very good anti-interference ability. Some substation automation systems also use fieldbus technology, such as Lonworks and CAN bus. Fieldbus has high anti-interference performance, moderate network transmission speed, low cost, and convenient construction. c) Control system: The station control unit adopts high-performance workstations or dedicated hardware, with strong processing and storage capabilities and high reliability. The monitoring and protection units are all divided according to the primary equipment installation unit, and are located near high-voltage circuit breakers and on low-voltage switchgear. The station control unit and the monitoring and protection unit are connected via serial port or network. Due to the decentralized function and composition, the scale is scalable and can meet the needs of different voltage levels. However, these products also have problems such as high price, less than ideal openness, and inability to fully meet the domestic requirements for the use and management of primary equipment. 3.2 In China, substations with voltage levels of 220-500 kV are basically operated by manned personnel, and most of them only send telemetry and remote signaling information. However, the development direction of this type of substation automation system is still the adoption of a completely decentralized substation automation system. Substations of 110 kV and below are mostly required to be designed for unmanned operation. According to the level of automation achieved, they can be divided into two categories: one is the remote control unit (RTU) mode, and the other is a completely new integrated automation mode. In a general sense, a remote control unit (RTU) is a centralized, single-CPU automated device with "four remote" functions (remote control, remote monitoring, remote telemetry, and remote control operation). It also adheres to unified communication protocols and technical standards. All signals are centrally acquired by the RTU, and remote control and remote adjustment commands are output through the RTU's hard contacts and introduced into the secondary control circuit via control cables. Now, distributed RTUs with multiple CPUs working collaboratively have emerged. These can be modularized according to function or electrical unit, and their physical structure can be configured as centralized or hierarchical. AC sampling technology is widely used in RTUs. Furthermore, the RTU mode can also be configured with a powerful human-machine interface subsystem via a serial port. Other intelligent devices in the substation generally connect to the RTU through the serial port. RTUs generally cannot exchange information with digital protection systems; protection action signals still need to be acquired through relay contacts. Regarding the second method, its usage in China is as follows: a) Signal acquisition method: A distributed AC acquisition system is used, connected to the background monitoring master station via a serial port or network. Especially in 10 kV substations, the measurement and control components are integrated into the 10 kV protection device. Dedicated current input ports are used to connect to the measurement current transformers (CTs) based on the different sampling accuracy requirements of analog quantities. b) Control System: Station control units mostly use industrial PCs, whose performance-to-price ratio is inferior to computer workstations and computer servers. Monitoring systems generally retain RTU devices, using them for information acquisition and transmission to dispatching at all levels, and exchanging information with the monitoring system. c) Digital Communication Methods: Field communication mostly uses RS serial communication buses, with a few using CAN and London's fieldbuses. However, the communication protocols of equipment from different manufacturers are numerous, wasting a significant amount of manpower in software and hardware development and causing considerable inconvenience for users in equipment selection, operation, and maintenance. Furthermore, due to limitations in communication protocols and the incomplete functions of the dispatching master station, integrated automation systems cannot provide the rich substation operation monitoring functions they offer when used as unmanned substations, wasting user investment. Overall, domestic substation integrated automation systems mainly purchase hardware equipment from abroad, while system software integration is provided by domestic research and development units, thus saving investment. [b]4 Functions and Composition of Integrated Automation System[/b] 4.1 Functions The substation integrated automation system based on fieldbus technology has the following main functions: a) Control and monitoring functions. It undertakes data acquisition (analog, switch, and pulse quantities) and equipment monitoring and operation control functions (which can be automatically operated or selected by the upper-level dispatcher or local system via keyboard, and can only be executed after verification), and can realize "four remote" functions. b) Automatic control and energy control. Such as automatic on-load voltage regulation of main transformer, automatic switching of power capacitor banks, low-frequency load shedding, automatic connection of standby power supply and automatic grounding detection, etc. c) Metering function. It transmits the substation's operating measurement values ​​to the power grid control center and uses pulse energy meters to accumulate electricity. d) Relay protection function. It realizes the safety protection of various components, lines, busbars, etc. in the substation, and can communicate with the monitoring system. e) Other safety monitoring functions. It effectively prevents electrical misoperation through operation and interlocking functions; when the system fails, it can complete event sequence recording, accident replay and fault waveform recording; it has over-limit alarm and abnormal state alarm functions. f) Interface function. Responsible for connecting different layers within the system. g) System function. Enables coordinated and optimized control at the substation level and facilitates communication with a remote control center. 4.2 Hardware System Design The substation integrated automation system adopts a completely distributed system structure, which can be divided into three layers: the substation layer, the bay (unit) layer, and the equipment layer. The communication system will utilize CAN bus technology, as shown in Figure 1. [img=604,391]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gddl/2000-2/31-1.jpg[/img] The equipment layer includes primary equipment such as switches, transformers, and TA/TV. With technological advancements, the primary equipment in substations has become intelligent electronic devices (IEDs) due to the presence of intelligent sensors and actuators. These devices not only digitize field data but also have computer data communication interfaces, allowing them to freely exchange information with other equipment. Furthermore, it can calculate and analyze many other data that are difficult to measure directly, such as harmonic components, sequence current, and sequence voltage, based on the results of direct measurements. Utilizing the storage capacity of a computer, intelligent devices can also perform statistical recording functions. The bay unit layer includes protection equipment, data acquisition and control equipment, and indicating instruments, and in a distributed substation integrated automation system, it consists of independent protection and I/O units. The substation layer typically refers to the station-level computer, which can employ a multi-functional SCADA system based on engineering workstations and TCP/IP networks to perform functions such as data collection and processing, database management, anomaly detection and alarm, optimized control, and human-machine interface. 4.3 Selection of Communication Method The overall structure of a distributed substation integrated automation system mainly depends on the selection of the communication system, and the overall performance of the system is largely determined by the quality of the communication system. The communication network between the substation level and the bay unit level adopts a bus-type technology solution based on CAN network because this solution has the following characteristics: a) It is easy to implement dual-network backup and easy to improve performance through multiple networks; b) It is easy to integrate with I/O units and protection units and easy to achieve high-speed data exchange; c) It has high network arbitration efficiency and rich information priority levels, which can ensure the real-time nature of emergency information; d) It has strong anti-interference ability; e) It has low cost and simple construction. Communication with remote dispatch automation system and centralized control center adopts serial communication bus or dedicated remote control channel, and communication with remote diagnostic computer can be achieved through the connection of MODEM and telephone network. Therefore, the communication system of the whole system is hybrid, which can provide the most suitable communication method for different objects. 4.4 Software System Design The software of the system consists of two main parts: PC software part and module software part. The PC software part runs on the Windows system platform and consists of device configuration tools, network card drivers and human-machine interface (MMI). Equipment configuration tools are used to configure and download field devices; network card drivers serve as a bridge for communication between equipment configuration tools, human-machine interfaces (HMIs), and IED devices; the HMI allows users to visually and in real-time observe and control the information and status of field devices. [b]5 Conclusion[/b] Since the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE) have agreed that, for the benefit of the power industry, the "Substation Communication Networks and Systems" standard will be the sole international standard for communication within substations, my country has also adopted the transmission protocol of its existing IEC 60870-5-103 relay protection equipment information interface supporting standard. Therefore, in the design process, equipment conforming to this standard should be used as much as possible to ensure the safety of substation automation equipment. Considering the overall safety of substation automation equipment, a substation integrated automation system based on fieldbus technology will become the long-term direction of substation automation. [/align]