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Maintenance and Failure Analysis of Electric Actuators

发表时间:2019-02-14 13:36:36 Article source: Publication time: 2019-02-14 13:36:36

Electric actuators can be divided into two categories: straight stroke and angular stroke (in addition, there is a multi-turn type, which can be converted into angular stroke and straight stroke through a two-stage reduction gearbox). It is the main type of electric valves and electric dampers. The actuator is an indispensable part of the automatic control system. Its main task is to proportionally convert the control signal sent by the regulator into linear or angular displacement to drive the regulating mechanism such as valves, baffles and dampers to achieve Automatic control is widely used in the field of automatic control of industrial sectors such as electric power, metallurgy, petroleum, and chemical industry. In the past 10 years, due to the rapid development of electronic technology, electric actuators have also developed very quickly in intelligence. At present, more and more intelligent electric actuators have appeared. It uses microprocessors to complete the measurement of various parameters, Calculation, control and output enhance the flexibility of the performance, use and maintenance of the adjustment system.

First, the common failure analysis of electric actuators

To improve the operational reliability of electric actuators, it is necessary to reduce and eliminate faults as much as possible. In fact, such faults are diverse. It is mainly caused by the failure of a certain component, comprehensive factors of components / components in the system, electrical, secondary circuits, and external factors. Some faults can be solved by readjusting methods. Some faults are due to long use time and poor accuracy, and need to be repaired and replaced to restore their performance. Others are due to design defects that require manufacturers to improve to eliminate them.

1, the valve does not close

There may be many causes of valve closing failure, but generally there may be the following reasons, and you can check them one by one based on these reasons.

1) There is a large deviation in the analog adjustment signal or the electric actuator itself does not calibrate the adjustment signal acquisition. This only happens in applications where the valve opening needs to be adjusted arbitrarily. The elimination method is also relatively simple. You can directly use the ammeter to measure whether the adjustment signal is accurate (the measurement signal needs to be disconnected from the actuator or the ammeter is connected in series). If the problem of the adjustment signal is eliminated, the Input signal for calibration (most electric actuators provide this function).

2) The zero position of the electric actuator is set incorrectly. The mechanical zero set by the electric actuator is inconsistent with the fully closed position of the valve. At this time, the zero position of the electric actuator needs to be set again.

3) The torque or thrust of the electric actuator is insufficient. The pressure in the valve may be relatively large. The torque (or thrust) required to drive the valve exceeds the output torque (or thrust) of the electric actuator, especially in the fully closed position of the valve. Need to push more often. This may be a problem in the selection of electric actuators, or it may be that the torque of the electric actuators is sufficient, but the valve itself is caused by Cather after using the valve for a period of time. At this time, the valve should be cleaned or the electric motor with a higher thrust should be replaced. Executive agency.

4) Foreign matter stuck in the valve. Pipes must be cleaned, and valves may need to be disassembled to remove foreign objects.

2.The electric actuator can only run in one direction

1) It is usually caused by a fault in the control board. Generally, some components of the motor drive are damaged. Only the electric board can be replaced. If a single-phase motor is used, the split-phase capacitor may be damaged.

2) Detect if the motor wire is coming off

3) The motor itself is damaged

3. The tracking is not in place, the valve position does not correspond to the adjustment signal, and the error is large.

1) Is the dead zone setting too large? Normally, electric actuators have a dead band setting, which usually ranges from 0.5 to 5%. This parameter has a very large impact on control accuracy. Usually, a dead band setting of 1% is more reasonable.

2) The adjustment signal has a large error. This situation can be measured directly with an ammeter

3) The electric actuator does not calibrate the adjustment signal

4) The electric actuator was developed in advance by the limit or reached the mechanical zero or full position. At this time, the mechanical zero position and the full position of the electric actuator need to be reset. If necessary, the limit switch needs to be adjusted And even some electric actuators need to adjust mechanical limit stops.

4.Electric actuator vibration

1) Check if the dead zone setting of the electric actuator is too small. Generally set to about 1% is more appropriate, if there is still oscillation, you can appropriately increase the deadband setting value.

2) Some electric actuators have a motor brake, and the brake can be switched between manual and electric (such as DKJ \ SKJ series). When switching to manual, the motor brake is not activated, which can protect the manual operation of the electric actuator. Easy to operate, when switching to the remote controller, the transfer switch should be set to the electric state. Sometimes it is possible that the motor brake itself is damaged and only replaced.

3) The adjustment signal is unstable. Replacement of IO modules, as well as field cables, should use screened cables.

4) Are there any large interference devices around? Especially those high-powered devices, if turning off these devices can solve the problem, it proves that the problem lies with these devices

5) There is a problem with the control board of the electric actuator, or the anti-interference ability of the control board of the electric actuator is not strong.

Maintenance and maintenance of electric actuators

Electric actuators are mechatronic products, which are mainly composed of motor, bearing, gear transmission system and electronic parts. According to the reliability data published by the US military standard MIL-HDBK-338, mechanical failures of electric actuators are mainly concentrated in bearings. In terms of electrical appliances, the problem is mainly on the control circuit board, and sometimes the motor fails. In the motor failure: winding failure accounts for 20%, bearing failure accounts for 45%, slip rings, brushes, and commutator damage account for 5%. Others account for 30%; in bearing failures: lubricants deteriorate and disappear 45%, pollution accounts for 30%, erosion accounts for 5%, misadjustment accounts for 5%, corrosion accounts for 5%, and other accounts for 10%. It can be seen that good maintenance management can improve the reliability and effectiveness of electric actuators.

1. Strengthen the cleanliness management of lubricating oil The biggest feature of electric actuators is the need to use lubricating oil, whose viscosity changes with oil temperature. If the viscosity is too low, the wear of transmission components such as turbine worms and gears will increase, which will reduce the transmission accuracy. If the viscosity is too high, the operation will be poor. And the cleanliness management of lubricating grease is more difficult. The wear and tear of transmission components such as turbine worms and gears, the infiltration of impurities and moisture generated by aging, the loss of internal coatings, and corrosion will affect the cleanliness of lubricating oil.

2. Eliminate grease leakage in time. Due to the high frequency and high speed of electric actuators, it is difficult to avoid shocks. This is an important cause of grease leakage. Once the grease leaks, it needs to be resolved in time.

3. Improve the working environment and use conditions of electric actuators. The reliability and life of an electric actuator are directly related to its use, environment, personnel knowledge and other factors. Only by improving its working environment and use conditions in maintenance management, and putting people first, can it prolong its service life.

4. In the early stage of the fault, it is necessary to strengthen the maintenance. Of all the faults of the electric actuator, the proportion of the initial faults is generally high. Most of the initial failures are caused by preliminary errors in design, manufacturing, and installation. The discovery of these initial failures requires a certain amount of effort, and it takes time to resolve them. Therefore, it is necessary to strengthen the maintenance management during the initial failure period.

5. Do a good job of data management to prevent accidental failures. Occasional failures of electric actuators are generally difficult to predict. In order to prevent accidental failures, it is necessary to regularly check and maintain, and to master the maintenance data and historical archive data at a certain stage, which is very important for accurate failure judgment and routine maintenance.

6. Improving the professional knowledge of operation and maintenance personnel The mastery of the operation and maintenance personnel directly affects the maintenance management. In recent years, due to the change in the structure of operation and maintenance personnel, their knowledge and technology of electric actuators have been greatly improved. However, many operation and maintenance personnel still lack the due professional knowledge and technology. Most of the on-site operation and maintenance personnel are in a state of "seems to understand" about electric actuators, which is also where the weak link of maintenance management lies. In order to make it easier for operation and maintenance personnel to carry out on-site maintenance and management, it is necessary to have advanced consciousness when designing the electric actuator system, fully consider the implementation of easy maintenance management, and strive to achieve: the system should be simplified, the simple system failure rate should be low, and maintenance management Easy; high degree of standardization, good interchangeability, easy to repair; integration, combination, easy adjustment and inspection; introduction of new technologies such as fault diagnosis and location, fault tolerance / correction.

7. Since the damage to the control circuit of the electric actuator is the overwhelming majority, it is necessary to increase the service life of the control circuit board. Most of the damage to the control circuit board of the electric actuator is caused by water or moisture. There is an excessively high ambient temperature. Therefore, it must be ensured that the electric control room of the electric actuator is well sealed, and try not to let the water come in. If possible, you can make a canopy for the electric actuator. Most of the actuators can only reach IP67. This protection can only be short in the rain. Let it rain, and don't expose it to heavy rain.

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