1. DCS Control System Reliability DCS, short for Distributed Control System, was first applied in China in the mid-to-late 1980s to imported generator sets. Currently, its application is increasingly widespread, from large units to small heating units, making a significant contribution to the safe and economical operation of power production. For power plants, the reliability of the control system is crucial to the overall safety and reliability of the plant. Improving DCS reliability to ensure safe and economical power production has become an increasingly important task. Based on the author's experience in thermal control system maintenance in power plants, this article discusses how to improve the overall reliability of a DCS from the perspective of control system selection, equipment installation, program design and commissioning, and technical training. 2. DCS Control System Selection Whether in new units or in the upgrading of control systems for existing units, the challenge lies in selecting an ideal control system that offers the best possible quality at the lowest cost. Here, we will set aside the price of the control system for now and only consider the need to improve reliability. The following aspects need to be considered in the DCS selection process: (1) When selecting a DCS control system, priority should be given to control systems with good performance on similar units. Such control systems have passed factory tests and actual operation, and their reliability has been tested over time. (2) The hardware of the control system must have high reliability. Mature technologies are used in all aspects of the production process of electronic components. Electronic modules should preferably be hot-swappable. The computing and storage capacity of the controller should be sufficient, and the IO cards should have strong anti-interference capabilities. (3) The control system should fully adopt redundancy technology in terms of structure. The controller, network communication, etc. of the control system must be redundant, and the redundant devices must be able to achieve seamless switching. The use of redundancy structure can not only avoid the expansion of accidents due to local faults in the control system and ensure the safe and stable operation of the unit, but also ensure the online troubleshooting of equipment faults, thereby eliminating potential accident hazards. (4) The maintainability of the control system software should be good. In particular, the following aspects are crucial: Good program and software stability, preventing system or individual controller crashes; good system self-diagnostic capabilities, with error alarms for controllers and I/O signals; user-friendly human-machine interface, allowing online program modification and download; reliable spare parts and components, easy and quick to procure within 15 years at low prices; and good readability of the control system software, ensuring its configuration function blocks can easily meet the various process functions required by the DCS control system. 3. Construction Technology and Quality Strict regulations govern the installation of DCS control systems, making the selection of a qualified and experienced construction company particularly important. Once the control system selection is finalized, the construction company's technical personnel must be involved in the control system design, production of construction drawings, development of construction measures, and technical training. Before project commencement, a strict schedule must be developed based on the project timeline, requiring the construction company to organize its construction resources and submit its construction plan. During DCS installation and commissioning, special attention should be paid to the following issues: (1) During construction, attention should be paid to the reliable insulation between the cabinet and the ground and the reliable grounding of the cabinet busbar. At the same time, fireproofing treatment must be done for holes, etc., and the cabinet should have anti-vibration measures. (2) When laying cables, special attention should be paid to the separation of strong and weak currents, reliable grounding of shielding wires and anti-interference. During the wiring process, it is necessary to follow the design drawings. In the wiring, the cable and core wire markings should be clear and complete and can be maintained for a long time; the crimped terminals must be pre-installed with insulating tubes. (3) The environmental conditions in the electronic equipment room should be strictly controlled, and attention should be paid to fire protection, air conditioning, ventilation and lighting. In particular, ventilation and air conditioning should be mentioned. Since the DCS control system has strict temperature requirements, the air conditioning system should be put into operation as soon as possible. The air outlet of the air conditioner should not be directly facing the cabinet or other electronic equipment of the DCS to avoid condensate water seeping into the equipment and causing damage. At the same time, dust must not be allowed to enter the electronic card. Therefore, the electronic room should always be kept clean and the filter should be clean. Pay attention to dehumidification and temperature adjustment. 4. Program Design and Debugging Acceptance During the program design and acceptance process, the enthusiasm of all employees should be fully mobilized so that everyone can understand, become familiar with and master the DCS control system as much as possible. In configuration and acceptance, special attention should be paid to the following issues: (1) In the program configuration design, a control strategy to ensure the safe operation of the unit must be adopted. The logic criteria for protection or interlocking must be necessary and sufficient. For turbine speed, turbine lubricating oil pressure, etc., it is advisable to use a combination of hard-wired protection and software protection. It is recommended to use normally closed signals to ensure reliable protection. For important three-out-of-two protection signals, analog and digital signals should be combined. Under the premise of ensuring the safety of important main equipment, it is recommended to use normally open signals as much as possible to avoid malfunction of protection. (2) In the stages of control system selection, design, testing, acceptance, commissioning and online adjustment, program design and testing personnel must participate throughout the process. They should combine the problems existing in the use of similar control systems and strictly review the rationality of protection control logic design and configuration. During testing, all circuits must be tested comprehensively, and the results of each inspection and test must be carefully recorded. If any software-related problems are found, the supplier must be contacted immediately, and the situation must be fully reported to them so that the problem can be resolved as soon as possible. (3) Necessary backup measures must be in place: important protection and interlocking must have hard-wiring methods in addition to communication connections; for important regulating equipment, in addition to soft manual operation on the operator station, backup manual operation must also be provided so that important equipment can still be intervened in a timely manner when the DCS controller or I/O module fails. 5. Personnel management and technical training Once the DCS selection is determined, before system construction, hardware testing and program configuration, relevant training must be provided to thermal control engineers and operation personnel with strong practical experience. The training must be combined with the simulator and the actual system to ensure that the training is targeted. (1) Training for operators: Since improper operation may affect the performance of DCS hardware or software, which may indirectly affect the safe operation and economic indicators of the unit, it is necessary to widely solicit the opinions of operators during the process of DCS screen design and involve them in the design and debugging so that they are fully familiar with the operation changes of the control interface and know how to operate. For routine operations such as starting and stopping equipment, manual/automatic switching and accident prediction, complete operating procedures should be compiled and technical training and drills should be conducted. The commissioning stage of the DCS control system should be fully utilized to conduct comprehensive training for relevant operators. (2) Training for thermal control personnel: The training of thermal control personnel should take into account their respective strengths. Since the knowledge involved in the DCS control system is very broad, it is impossible to master it all in a short time. Therefore, the differences in the cultural quality and professional level of thermal control personnel should be fully considered, and priority should be given to thermal control engineers with better conditions to conduct more in-depth training in different aspects. Through training, they can gradually take on important responsibilities in the construction of the DCS control system, the establishment of network communication, the testing and acceptance of hardware, the design of program configuration, and the testing and adjustment of control loops. Simultaneously, it's crucial to fully utilize the problems encountered during equipment commissioning and phased operation. With the supplier's assistance and in conjunction with technical manuals, these engineers are required to analyze, diagnose, and resolve issues. Based on this, they provide "online" training to other thermal control personnel. Conclusion In industrial practice, control system problems are normal. However, as engineering technicians, we have a responsibility and obligation to minimize serious safety-impacting issues in control systems. For recurring problems in control systems, we must analyze them thoroughly, summarize them diligently, identify commonalities, and take targeted measures to improve them, enabling the DCS control system to better serve the safe and economical operation of power production.