The electronic electric actuator has basic functions such as stroke control, torque protection, manual electric switching and manual operation, remote and local control, and can supply the power command signal given by the upper control device and system (regulator, PLC or DCS ). Converted to the corresponding displacement, drive the final control part of the Zui (such as regulating valve, baffle, etc.) to the required position of the system, and then adjust and control the process parameters such as flow, temperature and pressure to realize the process control of the system. At present, in large domestic thermal power plants, electric actuators are widely used, but there are also many problems. This paper will explain the application and maintenance of electric actuators in thermal power plants from the following aspects.
1 Application status of electric actuators in thermal power plants
At present, a large number of domestic electric actuators such as DKJ ( ZKJ ) and DKZ ( ZKZ ) are used in thermal power generating units below 300MW. Advanced integrated intelligent electric actuators are generally used in new units above 300MW , represented by RotorkIQ series actuators.
DKJ ( ZKJ ), DKZ ( ZKZ ) and other series of domestic electric actuators have the advantages of simple structure, low price and easy maintenance. The shortcomings are mainly controlled by hard wiring. The fault cannot be self-tested, and the reliability of motor protection is not high. , prone to failure. The intelligent electric actuator generally adopts a fully enclosed and integrated structure, and adopts advanced microprocessors such as single-chip microcomputer to control the intelligentization of the actuator. It not only has a simple structure, but also has a low failure rate; even if there is a fault, it can pass the self-test. Discover and display the error code to the engineer to resolve the problem early. It has the advantages of intelligent control, high protection level, high control precision, light weight and good stability. In addition, it solves many of the problems of traditional electric actuators, such as flexible control of motor speed. In view of the above advantages, more and more new thermal power plants use integrated intelligent actuators.
2Electric actuator selection
In order for the electric actuator to perform stably in use, it is necessary to select a suitable electric actuator. The selection of electric actuators should pay attention to the following aspects:
( 1 ) Select the appropriate brand based on the importance of the executing agency in the system. If the actuators that play an important role in the system flow, such as the bucket adjustment control device for the blower, etc., choose a well-recognized mature brand, and the MTBF must be greater than one overhaul cycle.
( 2 ) Select the specific model according to the specific conditions on site. Each brand's actuator has a detailed description of its model, and users should carefully select the model according to their needs. For example, determine whether to use switch type or adjustment type, angular stroke or straight stroke, position feedback or no position feedback; determine the enclosure protection level and explosion-proof level according to the environmental conditions at the installation. The degree of protection of the enclosure refers to the anti-foreign material and waterproof rating of the housing of the electric actuator. It is represented by the letter IP followed by two digits. The * digit is represented by 1-6 for the foreign object level, and the second digit is 1-8 for the waterproof rating. . If the temperature is high, choose a model or split type that can adapt to high temperature. If the dust is large or under water, IP68 should be selected . It is very important to choose the model that adapts to the environment. Generally, this factor is easy to ignore. After Zui, the actuator is prone to failure or reduces the life of the actuator.
( 3 ) According to the requirements of the valve, choose the appropriate torque, which is important. When the electric actuator is actually applied in a thermal power plant, it is always found that the valve has a card, and the engine check has no card. This is because the actuator torque selection is too small; sometimes the valve selection is too large, and the valve stem is always broken. This is Because the selection torque is too large. The electric actuator with the right torque is good for protecting the motor and the valve. When selecting, it should leave a considerable margin and be verified according to the specific conditions. In addition, the appropriate electrical parameters should be selected according to the number of actions per unit time when the valve is working. Select the appropriate electric actuator type according to the voltage level used.
3 problems and solutions in the application
Although the manufacturing process and control method of the electric actuator are very advanced, due to the frequent operation of the electric actuator, various failures such as aging of the control components may occur.
3.1 Common faults and treatment methods of domestic electric actuators such as DKJ ( ZKJ ) and DKZ ( ZKZ )
The application of the above series of domestic electric actuators in 300MW units and below 300MW thermal power generating units is characterized by simple structure, mainly using hard wiring to realize the basic functions of electric actuators. All the circuits are hardwired to some electronic elements. The device is directly connected, it protects the motor through the fuse, thermocouple and torque switch, and the switch loop realizes a single operation of the switch through interlocking. The main problems with this type of electric actuator are the following:
( 1 ) Poor sealing
The wiring ports of this series of electric actuators are installed together with the stroke switch, torque switch, motor, etc. The environment of the thermal power plant is relatively poor. Due to the lack of attention or long service time during installation, the protective casing is damaged, causing rainwater and dust to enter the terminal box, and then flow from the terminal box to the control switch and the motor, causing the motor to be short-circuited or controlled. The switch is damaged. If the wiring cable inlet is higher than the cable outlet pipe, only the protective casing needs to be wrapped; if the wiring cable inlet is lower than the cable outlet pipe, in addition to the protective casing, the cable protection sleeve is also required. The hole in the lower part of the tube is prevented from being poured into the actuator when the water flows down from the outlet pipe. Our company has experienced the situation that the protective casing of the cable outlet pipe is broken and the rainwater is poured into the actuator, causing damage to the actuator; this situation has not occurred after the hole in the lower part of the protective casing zui. Therefore, maintenance and repair personnel should always check to find out the bad seal as soon as possible, and strive to eliminate the fault in the bud.
( 2 ) Aging of circuit components
This series of electric actuators mainly consists of mechanical actions, and thermal relays, travel switches and counters are prone to failure. Many of our electric actuators are damaged due to the failure of the thermal relay. As the torque protection switch increases with the running time, its protection is gradually lost. In addition, the thermal relay is damaged, the thermal power plant environment is poor, and the actuators installed on some pipelines are easy to jam, which leads to a large motor output. Causes damage to the motor. When the maintenance and repair personnel find that the motor has a fault due to overload, it is necessary to replace the thermocouple in time. Several times in our company, it was found that the actuator that had just been replaced was damaged soon after use. The maintenance personnel found that such a situation occurred because the torque set during commissioning was large, and the thermal relay lost its protection function. Therefore, for components, if they are found to be aging or lose their function, they must be replaced in time.
( 3 ) When the electric actuator is good or bad
Due to the long running time, the vibration of the power plant is large, and the control parts of the series of electric actuators are connected by hard wiring. Therefore, some control loops are prone to loose wiring, which leads to good actuator action. Bad. Therefore, it is necessary to tighten the wiring of the control loop and the power loop regularly, so as to eliminate the problem before it occurs.
3.2 Common faults and solutions for integrated intelligent electric actuators
The control principle of the integrated intelligent electric actuator is similar to that of the DKZ type, except that its implementation method is different, the protection function is more powerful, the online fault diagnosis capability is stronger, the control method is more, and the failure rate is lower; but there are also some problems. There are problems with the device itself, as well as problems with selection, as well as problems with device modules, aging of electronic components, and damage to vulnerable parts.
( 1 ) Control device crashes
In a technical transformation, our company selected an imported brand split-type electric device for the auxiliary wind baffle control actuator. The installation and commissioning were very smooth, but after the unit was started, many electric actuators could not operate, and the power was cut off again. After the operation is normal. The after-sales report is the original selection problem. Since the temperature of the boiler auxiliary wind baffle control is sometimes greater than 60 °C , the actuator control device is dead, and the previous crash problem is basically solved after the change. Some intelligent electric devices have a watchdog program. After the electric actuator control device crashes, it can be automatically reset and restarted; and some do not, after a crash, it needs to be powered off and restarted.
( 2 ) After the signal is broken, the electric actuator does not move in the correct position.
A 600MW unit induced draft fan control device uses an intelligent electric actuator. Due to loose wiring of the command line, the electric device loses the control signal, causing the fan blades to be fully closed, which makes the furnace pressure change greatly. During the failure analysis, the engineer re-learned the equipment specification and reconfigured the equipment to: when the electric unit lost the signal, the actuator did not act. The above problem occurred mainly because the field engineer did not fully understand the function of the new control device and misconfigured the device, causing the device to not operate correctly when the signal was lost. The integrated intelligent electric actuator has many functions. Only when we use it reasonably can it bring convenience to our work. Otherwise, it will bring a lot of trouble.
( 3 ) Large deviation between instruction and feedback
This phenomenon occurs in intelligent electric actuators, mainly because the feedback resistor element loses linearity due to wear, or the feedback transmission part is loose, or the command amplification module has a problem. The maintenance engineer should analyze the actual problem.
In short, for the fault handling of electric actuators, we must start from the phenomenon analysis, firmly grasp the basic principles and not relax, and use various scientific means for analysis and processing. In addition, preventive maintenance is required for electric actuators to avoid equipment failures. For intelligent electric actuators, it is necessary to make full use of their functions in order to detect problems as early as possible and to predict problems as early as possible.
Vault Room Construction,Vault Room In House,Vault Room Door,Vault Room
Hebei Yingbo Safe Boxes Co.,Ltd , https://www.yingbosafes.com