Introduction Since the late 1980s, China's thermal power units with a single unit capacity of 300MW and above have fully adopted distributed control systems (DCS), primarily controlling the turbines and boilers, significantly improving the automation and control levels of the turbines and boilers. To address the inconsistency in automation levels between electrical and thermal systems, from the mid-to-late 1990s, the generator-transformer system and plant auxiliary power system of the electrical system were gradually incorporated into the DCS for monitoring. However, the digital relay protection and automatic devices of the electrical system were connected to the DCS via hard-wiring, rather than through network communication. With the development of electronic and information technologies and the gradual marketization of power operations, thermal power plants have achieved rapid development in the application of automation technology. The integration of electrical and thermal automation in thermal power plants has become one of the key issues in current thermal power plant automation. Connecting some information from the Electrical Monitoring System (ECS) to the DCS via network communication has become a new development direction and has been widely used in newly built large and medium-capacity units. Many power equipment manufacturers and power plants are also actively exploring and experimenting with eliminating all hard-wiring and fully adopting communication-based access to the DCS. This article analyzes the advantages, disadvantages, and problems that need to be solved when ECS in thermal power plants is connected to DCS through three methods: hardwiring, hardwiring + communication, and full communication. It also looks forward to the future prospects and goals of ECS eventually achieving full communication. I. Hardwiring Method In the hardwiring method, electrical information is connected to DCS via hardwiring (see Figure 1). The connected information mainly includes digital inputs (DI), digital outputs (DO), and analog inputs (AI), using open contacts and 4mA~20mA DC signals. Figure 1: Hardwiring Structure. After adopting the hardwiring method, the DCS's CRT realizes the display and alarm of electrical information and the control and adjustment of electrical equipment, effectively improving the safety and reliability of the entire electrical control system. It also expands the control range of the DCS, realizing the integrated operation and monitoring of the boiler, turbine, and electrical systems. The advantages of the hardwiring method are: centralized arrangement of electrical I/O module cabinets, facilitating management and providing a better equipment operating environment; fewer signal transmission relay links, faster and more reliable response to field signals; and a lower probability of failure once the connecting cables are correctly laid, resulting in less maintenance workload. Although hard-wiring requires a higher initial investment, most power plants and design institutes still consider it the most reliable and fastest way to integrate electrical information into a DCS (Distributed Control System). Therefore, even with the gradual adoption of communication methods, hard-wiring is still retained for electrical interlocking and control systems that demand high reliability, real-time performance, and determinism. However, hard-wiring also presents several problems in its implementation and operation. The main issues are as follows: 1) The DCS requires a large number of transmitters, I/O cards, cabinets, and connecting cables, resulting in complex construction and high costs. 2) The amount of information that can be integrated into the DCS is very limited, leading to poor system scalability. 3) Each power circuit requires a separate energy meter, but automatic meter reading is not possible. 4) Complex electrical maintenance and management tasks such as accident tracing, protection setting management, waveform analysis, operation tickets, and anti-misoperation interlocking cannot be performed, resulting in a low overall level of automation in the electrical system. 5) When feeding back plant power, remote operation of high-voltage standby transformers and high and low voltage plant power supplies is not possible because the DCS is generally not yet operational. 6) The plant power system has adopted a microcomputer-based integrated protection and control device (hereinafter referred to as the integrated protection device). Designed for bays, it integrates protection, measurement and control, and communication functions. It can transmit a large amount of information required by the DCS, such as voltage, current, power, energy, and protection action signals, through a network interface. Its accuracy and real-time performance fully meet the technical requirements. The hard-wiring method objectively leads to redundant hardware configuration and resource waste. In order to overcome the shortcomings of the hard-wiring method, especially for information accessed to the DCS for monitoring functions, it is necessary to consider replacing hard-wiring with communication methods. In recent years, network communication technologies represented by fieldbus and industrial Ethernet have been widely and successfully applied in power automation fields such as factory automation, substation automation, and DCS, and are becoming increasingly mature and stable. They provide mature operating experience for the networking and access of thermal power plant electrical systems to DCS. At the same time, the microcomputerization of the relay protection and automatic control devices of the electrical system also provides conditions for the networking and access of the electrical system to DCS. To improve the overall automation level of power plants, since the beginning of the 21st century, some power equipment manufacturers have successively launched ECS (Electronic Control System) for thermal power plants based on network communication. Representative products include Jiangsu Jinzhi Technology's DCAP-4000 system and Beijing Sifang's CSPA-2000 system. The method of accessing electrical information from thermal power plants to the DCS (Distributed Control System) has also changed to a hard-wired + communication method. Currently, the partial replacement of hard-wired systems with communication methods has gained widespread acceptance from power plant users and power planning and design departments. II. Hard-Wired + Communication Method Hard-wired + communication ECS systems generally adopt a layered distributed architecture. The system is divided into three layers: station control layer, communication layer, and bay layer. The system network structure is shown in Figure 2. The station control layer typically adopts a distributed architecture with client servers, consisting of servers, operator workstations, maintenance workstations, and communication gateways. It forms the central hub for electrical system monitoring and management, and interconnection with automated systems such as DCS, Management Information Systems (MIS), and Monitoring Information Systems (SIS). Although a large amount of electrical system information is accessed to the DCS via communication, it is primarily used for monitoring functions. The DCS does not have advanced application software specifically for electrical systems, a limitation determined by its positioning. The relatively independent monitoring of the electrical system through the ECS station control layer not only provides backup control for the DCS but also enables complex electrical maintenance and management tasks such as fault tracing, protection setting management, and waveform analysis through the analysis and processing of large amounts of basic information. This provides a dedicated platform for the operation, maintenance, and management of electrical systems, which is one of the key values ​​of ECS. Figure 2 shows a hard-wired + communication-based architecture. The communication layer typically centers on a communication management unit, which groups and transmits information. It connects to the station control layer's real-time backbone network via a 100Mbit/s Ethernet connection. Plant power integrated protection devices connect to the communication management unit via RS-485 or fieldbus. For third-party intelligent electrical equipment other than plant power integrated protection devices, such as generator-transformer protection, standby transformer protection, excitation systems, synchronizing devices, fast-switching devices, and DC systems, the communication management unit typically handles the conversion of communication interfaces and protocol formats, thus achieving complete electrical system networking. Simultaneously, the communication management unit can connect to the distributed processing unit (DPU) of the unit's DCS via a serial interface for information exchange. Currently, communication between the ECS and DCS can be achieved through two methods: the communication gateway at the station control layer and the communication management unit at the communication layer. Communication gateways typically use 100Mbits Ethernet, offering high data throughput, but require dedicated software modules for the DCS (Distributed Control System), which is significantly limited by the openness of the DCS. Communication management units and DPUs generally communicate via RS-485 interfaces and Modbus protocols, which is relatively simple and easy to implement. This also allows electrical information to participate in process interlocking, thus leading to its widespread application. The bay layer includes distributed plant power protection devices (such as motor protection and control devices, low-voltage transformer protection and control devices, etc.), 380V motor controllers, generator-transformer group protection, plant power fast-switching devices, and other intelligent electrical equipment, completing functions such as data acquisition, protection, control, and data communication of field information in the electrical system. The ECS (Electronic Control System) using hard-wiring and communication was the first to introduce network applications into the electrical system of a thermal power plant, significantly changing the access mode of electrical information in the DCS (Distributed Control System). A large amount of information, such as voltage, current, power, energy consumption, and protection action signals, is accessed to the DCS via communication. Hard-wiring is still retained for switch inputs and outputs related to process interlocking and control, and sometimes only hard-wiring is retained for motor circuits related to thermal interlocking. Control of the plant auxiliary power supply circuit is also achieved through communication interfaces. This approach provides a new platform for the electrical operation and maintenance of the power plant, enabling the adoption of new system maintenance methods and enterprise management models, with the following advantages: 1) The DCS eliminates a large number of transmitters, I/O cards, cabinets, and connecting cables, reducing costs. 2) The information accessed to the DCS is comprehensive and rich, with the amount of information essentially independent of investment, and the system has strong scalability. 3) The integrated protection device can achieve high-precision metering of the plant auxiliary power system's electrical energy, eliminating the need for separate energy meters, and can transmit data to the ECS backend via the network to achieve automatic meter reading. 4) Through the electrical system backend, complex electrical maintenance and management tasks such as accident tracing, protection setting management, waveform analysis, operation tickets, and anti-misoperation interlocking can be realized, significantly improving the overall automation level of the electrical system. 5) When backfeeding plant power, remote operation of high-voltage standby transformers and high and low voltage plant power supplies can be achieved through ECS. In recent years, in newly built thermal power units with a capacity of 300MW and above, the electrical systems have achieved networking of varying ranges and transmit monitoring information to DCS through communication interfaces, providing users with tangible benefits in terms of improving the automation level and management and maintenance of the electrical system. However, ECS also faces difficulties and problems in its implementation, mainly as follows: 1) For DCS manufacturers, the elimination of a large number of transmitters and I/O cards has impacted market interests to some extent, and the need to invest effort in communication access work inevitably leads to some resistance. 2) Currently, 70% of domestic investment in DCS is used for imported equipment. However, the communication openness of imported DCS systems is greatly restricted. The communication cycle and data packet length significantly impact real-time performance. 3) Compared to hard-wired methods, this communication method involves more information transfer stages, resulting in a gap in reliability and real-time performance. Currently, most communication information is limited to monitoring data and cannot fully achieve the comprehensive communication goals expected by users. 4) ECS nodes are numerous and highly distributed, and multiple units require phased construction. This places high demands on system capacity, network architecture scalability, and the after-sales service capabilities of equipment manufacturers. Solutions from different manufacturers vary in quality, and problems such as network communication interruptions and slow information updates frequently plague users, increasing system maintenance workload and affecting the implementation effect of ECS and user confidence. 5) From an investment cost perspective, the complex configuration of the station control layer and communication layer in some projects leads to higher ECS investment, resulting in no significant cost reduction for the entire control system. 6) After the DCS was put into operation, users used ECS relatively infrequently and paid little attention to it. Therefore, the electrical maintenance and management functions of ECS are not yet fully developed. To address these issues, on the one hand, ECS manufacturers need to provide advanced technology, reliable products, and comprehensive services based on user needs, and continuously improve and innovate, especially in enhancing the reliability and real-time performance of network communication and providing rich and comprehensive electrical maintenance and management functions. On the other hand, power plants, design and planning departments, and DCS manufacturers need to embrace ECS with greater confidence and an open mind. All parties need to cooperate closely, focusing on truly serving power plant users, and plan and implement the interconnection of ECS and DCS effectively. DCS manufacturers should meet the openness, real-time performance, and flexibility requirements of heterogeneous system interconnection in terms of hardware and software configuration. III. The development and widespread acceptance of ECS through full communication has always revolved around improving the overall automation level of electrical systems and achieving seamless connection between ECS and DCS. Currently, communication information only monitors but does not control, which is still some distance from the full communication method truly desired by users. Currently, some domestic ECS manufacturers and power plants have made beneficial explorations in the field of full communication and accumulated certain experience, such as Yunnan Xunjiansi Power Plant and Xuanwei Power Plant. For the full communication method currently put into engineering application, the system network structure is shown in Figure 3. Figure 3 Full Communication Method Structure In this method, the communication management unit is configured according to the power plant process. The communication management unit participating in process interlocking control communicates one-to-one with the corresponding DPU. Since the number of motor protection devices in each process is small, the real-time communication is high and can fully meet the requirements of power plant process interlocking control. For electrical information that does not participate in process interlocking, it is accessed to DCS through the communication gateway of ECS station control layer. In this way, the control and interlocking of the electrical system are all realized through network communication. Although the real-time performance is somewhat different from hard wiring, it can still meet the technical requirements. In the transition to the goal of full communication, it is a bold and beneficial attempt. However, this method also has great difficulties, mainly: 1) In substation automation systems and DCS, control is realized through network communication, but the network structure is generally no more than 3 layers, and the interconnected devices are generally products and systems from the same manufacturer. In Figure 3, the control information transmission network has four layers. The limited openness of the DCS also affects the tightness of the connection between the two systems, and the reliability and real-time performance are greatly restricted. This is the main reason why most users and design institutes are hesitant to adopt this model. 2) The communication management unit is configured according to the process, and the large number of units increases the investment cost. At the same time, the plant motor circuits of a process often come from different power distribution intervals, and the cross-network cabling also increases the difficulty of construction and maintenance. In future applications, if the integrated protection device participating in process interlocking can separate control information and non-control information according to the different requirements of DCS and ECS, and connect to the communication management unit of DPU and ECS through independent communication interfaces, then the reliability and real-time performance of DCS information access will be greatly improved. However, the increase in communication load and control switching will put forward new technical requirements for the integrated protection device. At the same time, DCS manufacturers will inevitably face greater resistance in connecting devices with different communication interfaces and protocols when their market interests are more impacted. Therefore, exploring new models requires not only the strong determination of power plants and design institutes to fully cooperate with DCS and ECS manufacturers, but also the resolution of how to balance conflicting market interests. IV. Conclusion With the rapid development of China's power industry, power plant construction, especially the construction of large thermal power units with a capacity of 300MW and above, has progressed rapidly. ECS has also been widely applied. Under current conditions, the hard-wiring + communication method better addresses the requirement of integrated boiler-machinery control when ECS is connected to DCS. Regarding the problems encountered in practical applications, it is believed that through close cooperation, reasonable planning, and correct implementation among ECS ​​manufacturers, DCS manufacturers, power plants, and design institutes, these problems can be effectively resolved. With the increasing stability of ECS and the continuous development of communication technology, it is believed that in the near future, the full communication method will truly be widely accepted and applied by users.