Scheme for improving the reliability of DCS control system power supply

In recent years, the application level of DCS control in the field of process control of thermal power plants has been rapidly improved. DCS is the core of the unit unit control system, and its functions cover traditional DAS, MCS, FSSS, ECS, DEH, ETS and other thermal automation systems. The impact of DCS on the safe and economic operation of thermal power plants is increasing. The probability of DCS failures causing the auxiliary equipment trips and even unplanned outages of the units is significantly increased.

At present, China's computer technology is developing rapidly. Among them, computer control technology is developing rapidly, and its control ability is continuously improved. It is widely used in various fields. The power industry plays an important role in promoting the development of China's economy. The development of the power industry has a direct impact on the production and life of society. Computer control technology is also effectively utilized in this industry. The DCS control system is the core of the power industry control technology. It should be noted that the DCS control system is an electronic device that is affected by internal signal differences and the harsh external environment. Therefore, it is necessary to improve the reliability of the DCS control system and ensure the normal operation of the power plant, otherwise it will cause serious accidents and bring huge losses to the social production and life.

In the dcs system, many technical measures to improve reliability have been adopted. These technical measures are based on the following four basic ideas:

1 makes the system itself less prone to failure, the so-called failure prevention.

2 Minimize the impact of faults in the event of a system failure, so-called fault security and weakening of faults.

3 When the system fails, it can keep the system running, so-called fault tolerance.

4 When the system fails, it can be repaired without stopping the system operation, so-called online maintenance.

Based on these four basic ideas, various reliability measures are adopted in the DCS system to reduce the occurrence of accidents and the losses caused.

First, improving the reliability of the DCS control system requires the plant to manage and train the staff. Specifically, it includes two aspects.

First, train the system's operators. If the operator makes mistakes in the operation of the DCS control system, it will have a greater impact on the performance of the hardware and software of the DCS. In severe cases, it will threaten the operational safety of the unit and indirectly affect the economic indicators. Therefore, when the manager performs the production of the DCS screen, it is not possible to act alone. It is necessary to actively communicate technically with the operating personnel, so that the operators are fully familiar with all the operational processes of the control interface. Managers need to familiarize the operators with the complete operating procedures, and focus on the emergency drills during the training process so that the operators understand how to operate to deal with emergencies. The most important thing is that the management personnel should let the operators fully understand their processes and procedures when training the DCS control system.

Second, training of thermal control personnel is required. A wide range of knowledge is required when applying the DCS control system, but the thermal controller cannot fully grasp the control principle in a short time. Therefore, training of thermal controllers is required. Prioritize training, and focus on intensive training for thermal control engineers. The thermal control engineer can independently complete the following tasks, one is the establishment of the DCS control system and network communication, the second is the design work of the program configuration, and the third is the hardware test and acceptance work. In addition, if some problems occur during the debugging of the equipment, the thermal control engineer should be involved, and the relevant information should be used to analyze and solve the problems.

Secondly, to improve the reliability of the DCS control system, it is necessary to grasp the selection process of the DCS control system. In the selection process of the DCS control system, the following aspects should be noted.

First, if the control systems of some of the units on several similar units are operating well, priority should be given to these units. However, it is still necessary to pay attention to the operation status of the DCS system in other power plants, so as to provide more reference for the selection of tenders.

Second, ensure that the hardware of the selected system is reliable when selecting the DCS control system. Specifically, hardware needs are produced using proven technology and can be multi-faceted, such as hot-swap. From the software of the DCS system, it is necessary to ensure the computing and storage capabilities of the DCS system, especially to have good anti-interference ability.

Third, from the structure of the DCS control system, the DCS control system needs to adopt redundancy technology to ensure that local faults will not affect the overall safety and stability of the unit.

After the DCS has a problem, there will be cases where the device is out of control due to inoperability and unmonitoring. In the case of light, the outage of equipment affects economic benefits, and the serious ones endanger the safety of people and equipment. Therefore, in the design, we must carefully consider the following reliability of the system according to the specific conditions of the site:

(1) Power system

The power supply system of the DCS system is the basis of its operation, and the power supply load should not exceed 60% to avoid high-load operation of the power supply. At the same time, it is necessary to consider the use of high-quality power supply, generally using ups power supply, using two UPS to spare each other best, after a failure, the backup machine can be switched without disturbance, improve the reliability of the power supply. Do not use the same busbar of the UPS input power supply. According to the wiring of the electrical plant, take the different busbar power supply with high reliability. This will ensure that the power supply of the DCS system will not be affected after the electrical bus has a problem.

DCS power system (UPS, power cabinet, etc.) should be installed in the electronic equipment room that meets the requirements of dust-free, vibration-free, anti-corrosion, etc. when installing on site. At the same time, the cable hole is sealed before installation to prevent leakage of steam from the cable. The hole enters the power system and causes a short circuit in the power supply. After the DCS power supply is powered on, it is necessary to hang the "device live operation prohibition operation" sign on the UPS, power cabinet, etc., and it is not allowed to connect the DCS power system to the load unrelated to the DCS system, such as maintenance power supply, overhaul Lighting, charging equipment, air conditioning, etc.

(2) Redundant system

On-site considerations necessitate redundancy of important I/O modules, taking into account the N:1 redundancy structure of the operator station, thus avoiding equipment outages due to hardware failures in the card or operator station.

(3) Adopting backup measures

1 manual backup

For important control loops, manual backup methods can be used to increase reliability. Once the automatic control fails, use the manual operation station to directly operate. In this case, the manual operation station directly outputs 4~20mA or 1~5V analog signals to control the actuator or directly ground the device for operation, which can be manually controlled. production process.

2 automatic backup

Automatic backup is to set up another set or sets of spare control devices in a redundant manner. When the automatic control device in the running state fails, the standby control device automatically inputs to maintain the automatic control of the system. Automatic backup is a form of redundant system with redundancy of main control unit redundancy, power system redundancy, network redundancy, I/O module redundancy, operator station redundancy, and server redundancy. When the running equipment fails, the hot standby equipment will automatically and uninterruptedly operate without affecting the repair of the faulty equipment.

The DCS system itself continuously performs online fault detection during operation. Once a fault is found, the faulty device is isolated from the system so that it does not affect the normal operation of other devices. After the fault occurs, an audible and visual alarm will be issued at the same time. The maintenance personnel will analyze the cause of the fault according to the prompt of the alarm and deal with the fault as soon as possible to avoid the fault from expanding. In the process of processing, you should do a good job of on-site technical measures, do not easily restart the CPU, so as not to cause disturbance to the device.

If you need to restart the CPU, you need to cooperate with the operator to take precautions. Generally, the DCS resets the analog output signal when the CPU is reset. This allows manual switching control of the actuator and inverter. The actuator can also be used. Electrical mode or unplug the analog output card (actuator has a break signal hold function), after the system is normal, add the signal to the normal value and then power on the actuator and the card. However, it must be carried out according to the characteristics of the DCS itself. In some designs, there is a switch safety output (on, off, hold, etc.). If the safety output selected by the user during configuration is on, the switch will be issued when the CPU is restarted. Open instructions.

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