Abstract : Based on the design requirements of the first phase 2×660MW power generation project of Ma'anshan Dangtu Power Generation Co., Ltd., and combined with the specific circumstances of this project, this paper proposes a fieldbus application scheme and conducts a technical and economic analysis. It also identifies potential problems and countermeasures in the application of fieldbus technology. Keywords : Fieldbus, Technical and Economic Analysis 0 Overview Fieldbus, as defined by the International Electrotechnical Commission (IEC) 61158, is a digital, serial, bidirectional, multi-point communication data bus between field devices installed in the manufacturing or process area and automatic control devices in the control room. A control system composed of fieldbus and field intelligent devices is called a fieldbus control system, commonly known as an FCS (Fieldbus Control System). 1. Scheme Concept Based on the application of fieldbus technology, the preliminary design scheme for the fieldbus of the 660MW supercritical thermal power plant in this project is as follows: 1.1 Intelligent Transmitters will be connected via HART fieldbus. The intelligent transmitters currently installed in the power plant (such as pressure and differential pressure transmitters) are basically intelligent transmitters with HART communication functionality. HART fieldbus is a field communication protocol first developed by Rosemount Corporation in 1986. It superimposes digital signals onto the 4-20mA standard signals commonly used in process control instruments. This digital signal is converted into an audio signal using Frequency Shift Keying (FSK) technology. The protocol specifies a signal frequency of 1200bit/s. The average value of this audio signal sine wave is zero, so no DC component is added to the field analog signal. Therefore, analog and digital signals can be transmitted simultaneously on both lines without interference. Currently, most power plants only utilize analog signals from intelligent transmitters with HART communication functionality, while digital signals are not practically used. However, some power plants in China have already applied digital signals from intelligent transmitters with HART communication capabilities. For example, the Huaneng Weihai Power Plant Phase II project (2×300MW) sends the HART signals from all field intelligent transmitters (approximately 200 per unit) to a HART multiplexer and connects them to Rosemount's Equipment Management System (AMS). The Yangzhou No. 2 Power Plant sends the HART signals from its field intelligent transmitters (approximately 500 per unit) to the OVATION distributed control system, allowing for monitoring, management, and adjustment of operating equipment from a computer in the control room. According to relevant information, using intelligent transmitter HART signals and the AMS system is highly beneficial in improving work efficiency and enhancing the safety and economy of the units. Using traditional methods, during overhaul or routine maintenance, the pressure and differential pressure transmitters being inspected require tasks such as disconnecting/commissioning, power outages/restorations, disconnecting/connecting wires, and disassembling/installing. Inspecting a single transmitter requires 1.5 working days for intermediate to advanced maintenance workers. Using HART signals and AMS, the entire transmitter testing process is completed on a computer, requiring only about 15 minutes to test a single transmitter, significantly improving work efficiency. HART signals or AMS fully utilize the functions of the intelligent transmitter, allowing the computer to monitor the ambient temperature of the transmitter's installation environment. Based on the monitored temperature, decisions can be made regarding whether to implement insulation measures to prevent the measuring pipeline from freezing or damaging the transmitter. For fault alarms from field transmitters, HART signals or AMS help quickly identify the cause of the fault, shortening troubleshooting time. This project can utilize HART signals from intelligent transmitters to construct an equipment management system, thereby improving work efficiency, reducing equipment maintenance costs, and enhancing the accuracy and reliability of the measurement system. 1.2 Electric gates using fieldbus: In the Niederaussem power plant in Germany, fieldbus electric gates were used for automatic control tasks without special safety requirements (such as steam-water circulation, flue gas systems, and unit coordination). Fieldbus was not used for automatic control tasks with special safety requirements (such as boiler protection and burner management) or for closed-loop control designs for turbine generators (such as DEH). This project considers further expanding the scope of fieldbus electric gates. Not only electric shut-off gates but also electric regulating gates can use fieldbus. The system scope can also be further expanded, considering the application scope of fieldbus electric gates at the Niederaussem power plant in Germany. That is, except for automatic control tasks with special safety requirements and closed-loop control designs for turbine generators, all other electric gates should use fieldbus. The bus network of the fieldbus electric gates can use a redundant communication network to ensure the reliability of the control network. 1.3 Motors using fieldbus: The control principle is shown in the following figure. Due to the lack of mature experience among equipment manufacturers, some difficulties were encountered during system debugging and individual equipment debugging. The main issue was damage to the SIMOCODE, primarily caused by poor on-site environment and inadequate maintenance. Additionally, communication interruptions occurred. After these failures, anti-interference isolation measures were implemented for communication between the SIMOCODE and the DCS system. PROFIBUS active anti-interference modules were added, and appropriate interface devices such as Y-switchers and photoelectric converters were added. These improvements prevented similar failures from recurring. At Jiangyin Xiagang Power Plant, 400V and below motors are controlled via fieldbus, connecting to the distributed control system. For 6kV motors, start/stop command signals and motor start/stop signals can be hardwired into the distributed control system, while other signals enter via the bus. Both units are currently in operation, and the fieldbus control system is running stably and reliably. The fieldbus control of the power plant's motors has proven reliable in actual operation, and considerable experience has been accumulated. In this project, the voltage of the motors can be treated differently: motors of 400V and below are controlled via fieldbus, and all signals are connected to the distributed control system through the fieldbus. For 6kV motors, start and stop command signals and motor start and stop signals can be entered into the distributed control system through hard-wired signals, while other signals can be entered into the distributed control system via the bus. 1.4 Auxiliary Workshop Control System Currently, fieldbus technology has not been widely applied in the auxiliary workshop systems of coal-fired power plants in China. The auxiliary workshop systems of coal-fired power plants under construction that use fieldbus technology include: Zhejiang Huaneng Yuhuan Power Plant (2×1000MW), which uses fieldbus technology in the boiler feedwater treatment system and wastewater treatment system. Because newly built power plant auxiliary systems, such as coal conveying systems, dry ash conveying systems, electrostatic precipitators, condensate polishing systems, chemical dosing systems, steam and water sampling systems, circulating water chlorination systems, and wastewater treatment systems, often adopt a separate island bidding process. In this separate island bidding, process equipment and control systems and instrumentation are frequently bundled together, resulting in multiple suppliers providing control systems and instrumentation. Furthermore, fieldbus technology is still relatively new, and suppliers of auxiliary system process equipment lack understanding of fieldbus instrumentation and control systems, resulting in limited experience. Under these circumstances, having each auxiliary system process equipment supplier provide fieldbus equipment and control systems could impact the quality and construction schedule of the power plant's auxiliary control systems. Therefore, the application of fieldbus technology in the plant's auxiliary systems can only be achieved through separate island bidding for process equipment and centralized bidding for control systems. Based on the design principles of the unit fieldbus scheme and considering the process characteristics of the auxiliary workshops, a unified technical plan should be developed for the entire plant, with early arrangements to ensure that the quality and construction schedule of the auxiliary control systems meet the requirements. For auxiliary workshop systems such as boiler feedwater treatment systems, wastewater treatment systems, and water purification stations, fieldbus technology can be given priority. 2. Technical and Economic Analysis 2.1 After adopting fieldbus technology in the distributed control system (DCS), the number of I/O cards can be reduced, but the number of communication modules will increase significantly. Basic conditions for quotation: Approximately 9400 I/O points per unit, approximately 75 electric control valves, approximately 240 electric shut-off valves (including some pneumatic shut-off valves), approximately 110 motors of 400V and below, approximately 22 6kV motors, with no more than 15 electric valves per communication port and no more than 10 motors per communication port. The unit I/O point list is as follows: [table=551][tr][td=1,1,105]System[/td][td=1,1,56]AI4-20mA[/td][td=1,1,49]AIRTD[/td][td=1,1,49]AITC（E）[/td][td=1,1,53]AITC（K）[/td][td=1,1,56]AO4-20mA[/td][td=1,1,49]DI[/td][td=1,1,49]DO[/td][td=1,1,35]PI[/td][td=1,1, 49]Total[/td][/tr][tr][td=1,1,105]Boilers[/td][td=1,1,56]510[/td][td=1,1,49]0[/td][td=1,1,49]0[/td][td=1,1,53]0[/td][td= 1,1,56]79[/td][td=1,1,49]2409[/td][td=1,1,49]920[/td][td=1,1,35]0[/td][td=1,1,49]3918[/td][/tr][tr][td=1,1,105]Steam turbine [/td][td=1,1,56]418[/td][td=1,1,49]245[/td][td=1,1,49]150[/td][td=1,1,53]33[/td][td=1,1,56]94[/td][td=1,1,49]192 6[/td][td=1,1,49]718[/td][td=1,1,35]0[/td][td=1,1,49]3584[/td][/tr][tr][td=1,1,105]Electrical[/td][td=1,1,56]140[/td][td =1,1,49]4[/td][td=1,1,49]0[/td][td=1,1,53]0[/td][td=1,1,56]0[/td][td=1,1,49]650[/td][td=1,1,49]115[/td][td=1,1,3 5]17[/td][td=1,1,49]926[/td][/tr][tr][td=1,1,105]furnace remote[/td][td=1,1,56]0[/td][td=1,1,49]0[/td][td=1,1,49]0[/td][td=1 ,1,53]285[/td][td=1,1,56]0[/td][td=1,1,49]0[/td][td=1,1,49]0[/td][td=1,1,35]0[/td][td=1,1,49]285[/td][/tr][tr][t d=1,1,105]Machine remote[/td][td=1,1,56]0[/td][td=1,1,49]58[/td][td=1,1,49]99[/td][td=1,1,53]0[/td][td=1,1,56]0[/td][td=1,1 ,49]0[/td][td=1,1,49]0[/td][td=1,1,35]0[/td][td=1,1,49]157[/td][/tr][tr][td=1,1,105]Public machine and furnace (single unit)[/td][td=1,1,56]10[/ td][td=1,1,49]3[/td][td=1,1,49]2[/td][td=1,1,53]0[/td][td=1,1,56]1[/td][td=1,1,49]50[/td][td=1,1,49]22[/td][td=1, 1,35]0[/td][td=1,1,49]88[/td][/tr][tr][td=1,1,105]Electrical public (single unit)[/td][td=1,1,56]32[/td][td=1,1,49]0[/td][td=1,1,49]0[/ td][td=1,1,53]0[/td][td=1,1,56]0[/td][td=1,1,49]215[/td][td=1,1,49]48[/td][td=1,1,35]5[/td][td=1,1,49]300[/td][/t [r][tr][td=1,1,105]Circulating Pump Station (Single Unit)[/td][td=1,1,56]25[/td][td=1,1,49]25[/td][td=1,1,49]0[/td][td=1,1,53]0[/td][td=1,1,56]0[/td][td=1,1,49]68[/td][td=1,1,49]24[/td][td=1,1,35]0[/td][td=1,1,49]142[/td][/tr][tr][td=1,1,105]Summary[font=Arial] [/size][/font][/td][td=1,1,56][font=Arial][size=10pt][size=1]1135 [/size][/font][/td][td=1,1,49][font=Arial] [size=1]335 [/size][/font][/td][td=1,1,49][font=Arial] [size=1]251 [/size][/font][/td][td=1,1,53][font=Arial] [size=1]318 [/size][/font][/td][td=1,1,56][font=Arial] [size=1]174 [/size][/font][/td][td=1,1,49][font=Arial] [size=1]5318 [/size][/font][/td][td=1,1,49][font=Arial] [size=1]1847 [size=1]22 [/size][/font][/td][td=1,1,35][font=Arial] [ size=1]9400 [/size][/font] [ /td][/tr][/table]Distributed Control System (DCS) Vendor 1: The quoted price using a fieldbus solution is approximately RMB 1.5 million more expensive per unit than using a conventional DCS solution. Distributed Control System (DCS) Vendor 2: The quoted price using a fieldbus solution is approximately RMB 2.25 million more expensive per unit than using a conventional DCS solution. 2.2 Field Equipment 1) Electric Doors · Imported Electric Doors In today's new engineering projects, most electric doors designed for the system are required to use intelligent mechatronics products. In this case, by further clarifying the bus standards that the field equipment should comply with, the equipment can be connected to the fieldbus system with minimal cost increase. On average, each imported fieldbus electric door is about RMB 10,000 more expensive than an imported intelligent integrated electric door. • Domestic electric gates: Since domestically produced fieldbus electric gate actuators currently lack mature application experience, the fieldbus electric gate actuators for the supercritical units in this project will be imported. However, the price difference between imported and domestically produced fieldbus electric gate actuators is significant, averaging approximately 30,000 to 45,000 RMB per unit. 2) Motors: Through research, it was found that after adopting fieldbus intelligent control units in large quantities for motor control units, the cost per motor's fieldbus intelligent control unit is only about 5,000 RMB more than a conventional control unit. 3) Field transmitters: Since most pressure and differential pressure transmitters used in power plants currently have HART bus protocol interfaces, using HART to access the distributed control system does not increase the cost for primary equipment in the field. The equipment management software for the transmitters costs approximately 200,000 to 300,000 RMB per unit. 2.3 Cables: Using fieldbus technology can save on installation materials such as cables and cable trays. In a conventional distributed control system (DCS) scheme, two control cables are required between each electric gate and the DCS, one control cable is typically required between each electric shut-off gate and the DCS, and approximately two to three control cables are required between each motor and the DCS, with each cable averaging about 120 meters in length. Using fieldbus technology requires only a small number of communication cables. Approximately 80 kilometers of cable are saved per unit. 2.4 Auxiliary System Compared to using a programmable logic controller (PLC), the fieldbus auxiliary system reduces some I/O cards, but also requires additional communication cards. Multiple devices can be connected to a single twisted pair or cable, saving significant cable and installation costs. However, the instruments used are digital and intelligent fieldbus instruments, which are currently more expensive than ordinary instruments. Therefore, overall, the economic cost is roughly the same. Based on the above economic comparison, a conservative calculation suggests that the fieldbus scheme will increase the cost per unit by approximately 5.85 million yuan compared to the conventional DCS scheme (the increased cost mainly comes from the fieldbus electric gates and actuators). After adopting fieldbus technology, distributed control systems, fieldbus electric gates, fieldbus motor control units, and fieldbus instruments all need to have fieldbus interfaces. These products are more expensive than conventional products, but the adoption of fieldbus technology will bring significant economic benefits to these electrical devices in terms of saving on cables, cable trays, cable ducts, cabinets, and maintenance and management during operation, as well as remote parameter setting and remote fault diagnosis. 3. Potential Problems and Preventive Measures in Fieldbus Technology Application 3.1 Potential Problems 1) Fully Utilizing the Advantages of Remote Diagnosis in Fieldbus Systems Compared with traditional systems, fieldbus systems based on intelligent field instruments have advantages not only in control but also in simple maintenance and automatic diagnosis and calibration management functions. However, in actual use in China, its management automation and remote diagnosis functions have not yet been applied. Therefore, the advantages of fieldbus systems in reducing operation and maintenance costs may not be fully realized in the near future. 2) Increased Engineering Commissioning Difficulty: Fieldbus technology incorporates many new technical elements and configuration parameters, making it difficult to master. Fieldbuses like FF are inherently complex, often encountering difficulties during commissioning and operation. Therefore, a strong technical team is needed to solve these technical challenges. In contrast, PROFIBUS is simpler and easier to implement. 3) Relatively Limited Range of Fieldbus Product Options: Fieldbus is a new technology still under development. The specifications and variety of intelligent field devices are relatively limited compared to conventional instruments, especially high-performance fieldbus controllers and intelligent field devices developed for power plants. This lack of widespread support for intelligent field devices, particularly domestically produced ones, limits the options available during system design, potentially leading to higher equipment prices in some cases. 4) Difficulty in Procuring Unified Fieldbus Standards: Current power plant infrastructure models involve design units compiling equipment specifications and construction units organizing procurement. Some equipment is procured by construction units, while others are supplied as part of process equipment or subcontracted. This procurement method makes it difficult to guarantee supply according to unified bus standards. Based on current realities, even when the technical specifications in the manual are very clear, the actual delivery on-site is often a different story. Different fieldbus standards are incompatible, resulting in wasted money and ineffective implementation. 5) The difficulty of designing a unified fieldbus standard is significant. Within design units, automatic control involves electrical, thermal control, and even system specialties, each with its own specific systems and field equipment. For example, in the main plant, the power distribution devices for pumps and fans are designed by the electrical engineering department, while the power distribution devices for electric doors are designed by the thermal control department. The difficulty of requiring a unified fieldbus standard for hundreds of devices during design and ordering is considerable. 3.2 Preventive Measures To ensure the engineering design achieves its intended goals, all parties involved in the project should strengthen their technical reserves and engage in extensive multi-faceted technical exchanges. Engineering technicians should strive to learn about fieldbus technology, deepen their understanding of fieldbus, and gradually develop the engineering application capabilities of fieldbus control technology. In practical operation, a comprehensive comparison should be made from a technical perspective, based on the characteristics and needs of the project, considering factors such as the technical performance, market share (domestic and international), product compatibility, domestic technical support, supplier reputation, after-sales service, price, compatibility, and ease of interface with other systems of various fieldbus systems. This comparison will help select and determine the type of fieldbus system. Fieldbus products with high international recognition, good reputation, numerous users, many supporting manufacturers, and superior performance are most likely to become industry, national, and international standards, thus ensuring long-term benefits for the user's investment. Furthermore, to ensure the effective and smooth implementation of the project, active technical exchanges with control engineering companies should be conducted before the project design. Through these exchanges, control engineering companies can understand the expected goals of the project in advance, allowing for thorough technical preparation. During these exchanges, each control engineering company will be required to provide a list of supporting manufacturers for fieldbus equipment such as electric gates, transmitters, and motor controllers, which they believe have demonstrated good application performance in previous projects, according to the PROFIBUS or FF bus standards, and to configure them based on the provided reference process system scheme. If necessary, field equipment can also be provided by a control engineering company to ensure the entire control system achieves good practical results. 4. Conclusion: Looking at the current applications of fieldbus technology both domestically and internationally, they can be broadly divided into two categories. The first is the application of fieldbus standard protocol technology in the remote I/O communication of distributed control systems (DCS). Almost all mainstream DCS manufacturers have application experience in this area, and there is considerable experience in domestic engineering projects. The second category is fieldbus control systems where intelligent field devices conforming to fieldbus technology standards are embedded with control modules that have controller functions, and these devices connect to the DCS using a communication method conforming to a certain fieldbus protocol standard. This represents a breakthrough in current engineering design and is a true fieldbus control system solution currently being discussed domestically and internationally, with the hope of widespread application. References : 1. Jiangsu Electric Power Design Institute. Author's Biography: Yin Baoli: Graduated from Shanghai Electric Power Institute in 1987 and was assigned to work in thermal control at Tianjia'an Power Plant in Huainan, Anhui. In 2007, he was transferred to Datang Anhui Ma'anshan Dangtu Power Generation Co., Ltd., address: No. 1 Zhengyuan Avenue, Taibai Town, Dangtu, Ma'anshan, Anhui; telephone: 0555-6822375.