Abstract : This article details the working diagram and principle of the electric actuator, and explains its application in a thermal power plant. It analyzes the fault factors and handling opinions at different stages, and clarifies important maintenance work, providing guidance for daily operation. Keywords : actuator , fault analysis, performance, maintenance 1. Overview China Shenma Group Nylon 66 Salt Company is a major production base for nylon 66 salt in China. Its thermal power plant uses nine electric actuators manufactured by Tianjin Automation Instrument Factory No. 7, with models A+RS100 and B+RS160. Adjusting the opening of the primary and secondary air fans and induced draft fan dampers of these three boilers, thereby controlling process parameters such as furnace temperature, flue gas oxygen content, and furnace negative pressure, is one of the important conditions for ensuring the stable operation of circulating fluidized bed boilers. 2. Working principle of electric actuator 2.1 Working block diagram The discrete regulating electric actuator used in the Nylon 66 Salt Company's thermal power unit is produced by introducing technology from Bernard Company of France. It mainly consists of two parts: a remote control actuator installed on site and a position positioner installed in the control room. Its working block diagram is shown in Figure 1: [align=center] Figure 1 Working block diagram of electric actuator[/align] The function of the position positioner is to compare and amplify the control signal and the field valve position feedback signal, and then output it to the actuator; the actuator drives the single-phase motor to rotate according to the signal sent by the position positioner. The valve position changes with the change of the reducer. When the difference between the valve position feedback signal and the control signal is less than the dead zone of the position positioner, the motor stops; at this point, one action process ends. 2.2 Working Principle Diagram This type of electric actuator has been operating in the Nylon 66 Salt Company for nearly five years. Due to its significant control role, it has repeatedly affected the long-term stable operation of the process. Therefore, understanding its working principle, being familiar with its fault phenomena, and mastering its daily maintenance are essential. Its working principle diagram is shown below: [align=center] Figure 2: Electric Mechanism Actuation Principle Diagram[/align] S1, S2: Stroke Limit Microswitches S3, S4: Torque Limit Microswitches RT: Overheat Protection Switch When the actuator power is turned on, AC contactors K1 and K2 are energized, and contacts K1-1 and K2-1 automatically connect. When the control signal is greater than the feedback signal, the positioner sends a signal to connect terminals 20 and 15, causing the motor to rotate forward, driving the reducer to run, and the cam to rotate as well (causing the feedback signal to increase); when the overtravel occurs, S1 disconnects, K1 is de-energized, K1-1 disconnects, and the motor stops. During rotation, at the instant of excessive torque, S3 is activated, relay K3 is energized, causing K3-2 to engage, and K3 is locked; simultaneously, normally closed contact K3-1 opens, K1 is de-energized, and the motor stops. When the control signal is less than the feedback signal, the positioner sends a signal, energizing contacts 20 and 16, causing the motor to reverse, with the same operating principle. Finally, the rotation of the reducer drives the single-gang conductive plastic potentiometer to rotate via the cam, and the current converter TAM2 outputs a 4-20mA DC feedback signal for remote indication. 3. Fault Analysis of Electric Actuators 3.1 Performance Indicators Whether an electric actuator can operate reliably and complete its specified functions within a specified time and under specified conditions depends on its performance indicators. Performance indicators are generally expressed by the Mean Time Between Failures (MTBF), which includes important parameters such as basic error, hysteresis, damping, and dead zone. These parameters, to some extent, reflect the performance of the electric actuator. 3.2 Main performance indicators and current problems The relevant technical parameters of this type of electric actuator are: 1 input channel, 250 ohms resistance, 1% basic error, 1.5% hysteresis, 0.5%~3% adjustable dead zone, and no disturbance in damping characteristics. Although some technical parameters of this type of electric actuator can be compared with those of foreign counterparts, due to the constraints of the imperfect operation mechanism of domestic manufacturers, there are also the following drawbacks: (1) Neglecting the research and development of basic technologies (2) Low quality of general components (3) Lax quality management of production by enterprises Due to the influence of the above drawbacks, many faults still occur in the operation of electric actuators. The following is a detailed introduction. 3.3 Fault analysis 3.3.1 Initial operation The initial operation period is the break-in period. The faults that occur during this period are relatively complex and the reasons are multifaceted, such as selection problems, design and manufacturing problems, or installation and environmental problems, etc. For example, if the torque is too small, it may affect its adjustment speed or even make it impossible to adjust at all. In practical applications, the following issues arise: The connection between the connecting rod and the actuator was not securely secured during design, leading to detachment; the power line and signal line were used in the same conduit during installation, causing significant signal interference; the presence of unshielded large motors nearby affects the stable operation of the actuator motor; the fuse for the positioner is too large, causing damage to its internal choke coil, etc. These problems must be observed, identified, and addressed promptly to avoid unnecessary losses. 3.3.2 Mid-term Operation During the mid-term operation, the overall performance of the electric actuator transitions from the break-in period to the adaptation period, exhibiting relatively stable performance. Problems often arise due to quality issues with individual electronic components, such as the position current converter TAM2, intermediate contactors K1 and K2, and over-torque microswitches. Besides promptly reporting these issues to the manufacturer, it is also necessary to compile statistics and prepare sufficient spare parts for replacement. 3.3.3 Late-term Operation In the late-term operation, the aging of components and wear of transmission parts become extremely serious. For example, aging of the motor coil can reduce insulation and cause unstable operation; poor motor lubrication can decrease operational stability; aging of the positioner's comparison coil or position current converter can reduce positioning accuracy; wear of the reducer's transmission components can cause the electric mechanism to become unadjustable. These problems should be checked regularly to prevent major malfunctions, and having a spare unit is also essential. Of course, objective factors also play a role in all failure factors, such as human error (stepping on the motor), jammed process baffles, and process misoperation. 4. Maintenance Based on the practical experience of on-site maintenance personnel, the maintenance of electric actuators should focus on different key maintenance measures according to their different usage periods. We usually need to do the following: 4.1 Regular Lubrication: The motor and transmission components of the electric actuator require lubricating oil, and the viscosity of the lubricating oil changes with oil temperature. Too low a viscosity increases wear on transmission components such as gears; too high a viscosity leads to poor operation. Therefore, regular lubrication can extend its service life. 4.2 Improving the Operating Environment: To ensure the reliability of the electric actuator, it is necessary to ensure that it operates in a suitable environment, avoiding environmental factors such as humidity that could cause short circuits or other malfunctions. 4.3 Regular Inspections: Regular inspections are crucial for timely detection and prevention of potential operational hazards. This helps in identifying fault causes and avoids unnecessary detours. 4.4 Thorough Fault Record Management: Every fault handled must be meticulously recorded, including the fault symptoms, fault analysis and troubleshooting process, fault cause, handling method, and preventative measures. This not only provides valuable reference for handling similar problems in the future but also improves the ability to identify fault causes through fault curve analysis, achieving twice the result with half the effort. 4.5 Enhanced Technical Training and Learning for Maintenance Personnel: Timely technical training and learning for personnel in thermal power positions can help them eliminate psychological stress, improve their skills, and ultimately achieve the goal of everyone being able to handle common faults. 5. Conclusion Overall, after nearly five years of practical maintenance, the electric actuators are performing satisfactorily at the Nylon 66 Salt Company. Of course, from a maintenance perspective, it is hoped that professional designers will fully consider the convenience of on-site maintenance and management when designing electric actuator systems. This includes simplifying the system as much as possible to reduce the failure rate; enabling online commissioning; using standardized and highly versatile components that are easy to repair; and appropriately introducing fault-tolerant/error-correcting functions. In this way, the maintenance of electric actuators will become increasingly easier, and their use in industry will become more widespread. About the author : Song Tongwei, born in 1972, male, graduated from Xi'an University of Electronic Science and Technology in 1995 with a major in Automation. He is an electronic engineer, mainly engaged in the application, maintenance, and technical management of various field instruments.