Abstract: This paper introduces the application progress of fieldbus technology based on the engineering example of the main and auxiliary control system of the 2×600MW supercritical unit at Shenhua Shengli Power Plant. It also briefly introduces the scheme for implementing the main and auxiliary machine control of large thermal power units using a fieldbus system. Keywords: Fieldbus; Supercritical; Equipment Management; DCS 0 Introduction Currently, the systems widely used for process control in thermal power plants are Distributed Control Systems (DCS) and Programmable Logic Controllers (PLCs). From the late 1980s to the present, DCS, with its advanced technology, rich control functions, and user-friendly human-machine interface, has gradually occupied the main control fields of boilers, turbines, and electrical systems in thermal power plants. PLCs, due to their strong logic processing capabilities, good environmental adaptability, strong system independence, and lower procurement costs, have become the preferred control system for auxiliary production systems (water, coal, ash) and unit auxiliary systems (soot blowing, air compressors, etc.). The fieldbus technology and products that began to develop in the late 1980s, and the control systems formed by them—Fieldbus Control Systems (FCS)—have triggered a revolution in the field of automatic control. Open, fully digital, and bidirectional multi-station communication networks, along with multifunctional intelligent field digital instruments, are the main features of FCS (Fieldbus Control System), which will bring about a huge leap in the efficiency of automatic control systems. 1. Introduction to FCS Applications Comprehensive informatization and multi-level automation are the future development direction of power generation enterprises. Establishing digital power plants is an inevitable path, and fieldbus systems are the foundation of digital power plants. In the past two years, major power generation groups have paid close attention to the application of new technologies in power plant thermal control automation and the huge benefits they generate. Huaneng Yuhuan Power Plant, Guohua Ninghai Power Plant Phase II, Shandong Zouxian Phase II Project, Jiangsu Wangting Combined Cycle Power Plant, Jiangyin Xiagang Power Plant, Guangdong Nanhai Petrochemical Cogeneration Project, Shaanxi Yangling Thermal Power Plant, Shandong Longkou Power Plant, Guang'an Power Plant, Shanxi Pingshuo Power Plant, and Shanxi Zhangshan Power Plant, among others, have successfully implemented the comprehensive application of fieldbus technology in their power plant peripheral auxiliary systems. Installation and commissioning were completed in a short period, and they were quickly put into stable and reliable operation. The successful implementation of numerous projects proves that the application of fieldbus in power plant auxiliary production control systems is entirely feasible. According to a report from the Mazatlan power plant in Mexico, the first unit (158 MW) to utilize a fieldbus control system, Unit 1, was put into operation on March 17, 1997. It operated continuously for 12 months without failure or maintenance, improving the dynamic response characteristics of the boiler. Compared to distributed control systems (DCS) and programmable logic controllers (PLCs), it reduced investment by 45% and shortened installation and commissioning time to three weeks. Following the success of Unit 1's upgrade, the plant immediately upgraded Unit 2 (158 MW), which was put into operation on February 14, 1998. Like Unit 1, this upgrade was highly successful, further reducing investment by 50% and shortening installation and commissioning time to one week. The Niederausem power plant in Germany has made comprehensive use of fieldbus technology. The plant employs both PROFIBUS-DP and HART-BUS fieldbuses. The entire system comprises 900 motors, 400 solenoid valves, 1000 valve positioners, and electric actuators, all intelligent devices connected to the DPU via PROFIBUS-DP. By adopting the PROFIBUS fieldbus system, true plant-wide monitoring is achieved, providing more comprehensive and effective equipment diagnostic functions, enabling remote programming and maintenance of field devices, achieving centralized management of plant-wide data, making condition-based maintenance possible, and providing more equipment information to optimize operation and maintenance. The successful application of PROFIBUS fieldbus at the Mazatlan power plant in Mexico, the K unit at the Niederhausen power plant in Germany, and the recent FF fieldbus at the Shanghai SECCO project has greatly stimulated the enthusiasm of domestic power generation groups and design institutes for applying fieldbus technology. Huaneng International, aiming to maintain a leading position in the application of new power generation technologies in China, and focusing on leading advanced technology trends, reasonably controlling project costs, and comprehensively improving the automation level of power plants, has fully applied fieldbus technology to the unit control in the design of the 2×1000 MW units at the Nanjing Jinling Power Plant and the 2×600MW units at the Jiutai Power Plant. China Shenhua Energy Company Limited intends to use the Shenhua Shengli Power Plant Phase I project (2×660MW units) as a pilot unit to fully adopt fieldbus technology in the main and auxiliary control systems. The control scale of fieldbus technology is far greater than that of other power plants both domestically and internationally that have applied it. 2. Introduction to FCS Application at Shenhua Shengli Power Plant The Shenhua Shengli Power Plant is located in Xilinhot, Inner Mongolia. The planned capacity is eight 600MW units, with Phase I consisting of two 600MW units. Due to the advanced nature of fieldbus technology, which can significantly reduce investment and improve unit operation and maintenance, Shenhua Group decided to fully adopt a fieldbus system in the main and auxiliary control systems of the Shenhua Shengli Power Plant. The scope and scale of fieldbus adoption in this project represent the largest engineering application of its kind in China to date. 2.1 Application Principles of Fieldbus in Shenhua Shengli Power Plant (1) Protection of main and auxiliary machines that affect the safe operation of the unit is not included in the fieldbus, such as: Boiler Safety Monitoring System (FSSS); Steam Turbine Digital Electro-hydraulic Control System (DEH); Steam Turbine Emergency Trip System (ETS); Bypass Control System (BPS); Sequence of Accidents (SOE). (2) Switch-type pneumatic valves and solenoid valves used for interlock protection are not included in the fieldbus. (3) Domestic electric doors are not included in the fieldbus due to imperfect fieldbus interfaces and lack of corresponding testing and application practices. (4) Switching instruments, such as pressure switches, level switches, and temperature switches, are not included in the fieldbus. (5) For regulating pneumatic actuators used in non-critical regulating circuits, they are included in the fieldbus. The following critical circuits use conventional hard wiring + HART: feedwater, steam temperature, forced draft, induced draft, and coal mill. (6) For regulating electric actuators, those used in non-critical regulating loops are incorporated into the fieldbus, while those used in critical loops (water supply, steam temperature, air supply, induced draft) are implemented using hard-wiring + fieldbus. (7) For on/off type valve electric actuators, those used in non-critical systems are incorporated into the fieldbus; those used in critical systems complete normal control functions (or only collect information) through the fieldbus, while protection and interlocking functions are implemented through DCS hard-wiring. (8) Signals for main unit/auxiliary unit protection and critical interlocking are retained using hard-wiring. (9) 380V motors use the fieldbus, and 6kV motors are also incorporated into the fieldbus. (10) Temperature measurement points of main unit/auxiliary units use remote I/O. (11) Measurement signals used only for monitoring use the fieldbus. (12) Plant power supply system uses the fieldbus. (13) Closed-loop control functions and function group sequential control logic are completed in the controller. (14) Air-cooled island frequency converters also use the fieldbus after adopting special interference isolation measures. 2.2 Preliminary Scheme of Fieldbus in Shenhua Shengli Power Plant (1) Application Scheme of Main Control System The main control system of Shenhua Shengli Power Plant includes various control functions such as Data Acquisition System (DAS), Analog Control System (MCS), Bypass Control System (BPC), Sequential Control System (SCS), Boiler Furnace Safety Monitoring System (FSSS), Steam Turbine Digital Electro-hydraulic Control System (DEH), Feedwater Pump Steam Turbine Digital Electro-hydraulic Control System (MEH), and Electrical Control System (ECX). These are crucial for the safe operation of the unit and have the highest requirements for real-time performance and reliability. By adopting DCS/FCS from well-known foreign brands with engineering experience in fieldbus technology, the fieldbus control system can be put into operation on schedule and reliably, minimizing engineering risks. (2) Application Scheme of Auxiliary Control System In Shenhua Shengli Power Plant, the auxiliary control system of boiler feedwater, external water network, condensate, fuel network, ash/slag network and desulfurization control uses a fieldbus control system. The boiler feedwater, external water network, condensate, fuel network, ash/slag network and desulfurization control system are connected by a fast industrial Ethernet, and the auxiliary control room monitors them centrally. The auxiliary control and monitoring network utilizes mature network and monitoring technologies. The system structure is as follows: all peripheral control systems of the entire plant first converge to their respective subnets, and then the subnets connect to the core switch of the plant's auxiliary network. The entire auxiliary control network consists of a redundant dual-star topology. The auxiliary network center is equipped with data servers, SIS interface servers, simulation interface servers, and operator/engineer workstations to meet the plant-wide auxiliary control requirements. 3. Conclusion Although the Shenhua Shengli Power Plant's comprehensive application of fieldbus in its main and auxiliary systems is still in the design and bidding stage, rationally planning the plant's automation and information architecture, reducing project costs, and improving the plant's automation and information management levels, along with a pragmatic and proactive scientific attitude to address the opportunities and challenges brought by new technologies, should be the essential professional qualities and technical skills required of those engaged in power construction. Fieldbus technology is basically mature. We should seize the current excellent opportunities in power construction, diligently learn and master fieldbus technology, and actively and steadily solve problems existing in engineering applications. Investors, construction parties, and design institutes should all change their mindset and work with equipment suppliers to promote the application of fieldbus technology in power plants, enjoying the benefits and achievements brought by the new technological revolution. The comprehensive application of fieldbus technology in the main and auxiliary systems of Shenhua Shengli Power Plant will bring tangible benefits to the safe and economical operation of thermal power plants, as well as to the improvement of management level and the construction of information-based power plants. References: [1] Han Pu. Computer monitoring and control of thermal power plants. Beijing: China Water Resources and Electric Power Press, 2005. [2] Yan Yuping, Cui Yiqun, Wang Chunli, et al. Successful application of fieldbus control system in thermal power plants. China Electric Power, 2007, 40 (3). [3] Cui Yiqun, Yan Yuping, Wang Chunli, et al. Research on the application of FF and Profibus fieldbus in thermal power plants. Thermal Power Generation, 2006, (2). [4] Zhou Ming. Fieldbus control. Beijing: China Electric Power Industry Press, 2001. [5] Wang Huifeng, He Yanqing. Principles and applications of fieldbus control system. Beijing: Chemical Industry Press, 2006. [6] Shen Jun, Hang Weihua, Liang Xiaocong. Application of fieldbus technology in thermal power plants. Electric Power Information Technology, 2008, 6(6). For details, please click: Discussion on the Application of Fieldbus Technology in the Main and Auxiliary Control Systems of Large Thermal Power Units