Common fault analysis and processing of valve electric actuator

Valve electric actuators have been widely used in the industry, but because of the large number of manufacturers producing electric actuators, the working principle is different, and the reliability of work varies greatly. Therefore, the electric actuator is a kind of equipment with high failure rate. Based on my own experience in the work, I analyze the common faults of the electric actuator and propose corresponding solutions.

The electric actuator mainly consists of a power board, a main board, a stroke detecting device, a torque measuring device, an AC contactor or an inverter, a motor, and a speed reducer. The electric actuator uses a small motor to drive the first-stage speed reduction mechanism worm gear, and the valve can output more Rotational motion, angular motion, and linear motion, the motion output form of the electric actuator is determined by the characteristics of the valve being controlled. If the operating torque required by the valve is particularly large, such as greater than 2000 NM, the secondary gearbox is usually added, the electric actuator directly drives the secondary gearbox, and the secondary gearbox drives the valve to move; the electric actuator Protection usually includes valve position protection, torque protection, motor overheat protection, motor stall protection, control unit fault protection, power failure protection, etc. The handling of faults should be carried out in a targeted manner according to the alarm information of the electric actuator.

1. The actuator position of the electric actuator is lost:
1.1 Battery power loss
When using the incremental encoder to measure the stroke, the actuator must have a battery as the auxiliary power supply, the AC power supply disappears, the change of the electric actuator valve position can still be detected by the incremental encoder, and the electric actuator is fully open and fully closed. No change occurs. If the AC power supply disappears, the battery power is exhausted. When the actual valve position of the electric actuator changes, the incremental encoder cannot detect the change of the valve position, resulting in the loss of the valve position. When the AC power is restored again. Some manufacturers have a default valve position of 50%; now some manufacturers using incremental encoders have improved their hardware to increase the capacitance loop. When the AC power disappears, the capacitors store energy to save the valve position, but electric The actuator cannot be operated manually without battery power, otherwise the valve position will still be lost. Therefore, when the battery is low, replace the battery in time.

1.2 hardware damage
The actuator of the electric actuator is disconnected, the encoder input voltage is too low, the gear of the stroke transmission is damaged, the encoder circuit board is corroded, the board stroke detection and the storage component are damaged, all of which can cause abnormal changes or loss of the valve position. Under the premise of normal encoder input voltage, replace the main board or replace the stroke encoder and eliminate them one by one.

2. Electric actuator torque failure:
2. 1 Torque protection refuses to move
Measuring the output torque of the electric actuator, mainly including mechanical protection switch, motor current voltage and power measurement and calculation torque, sensor type protection device: mechanical torque protection switch is used before 2000, which is a transitional product, now Some low-end electric actuators are still used. This kind of torque protection switch can only provide switching quantity for torque protection, can not provide real-time data of process torque, and has large measurement error. Calculate the phase angle between motor current voltage and current and voltage. The torque needs to be realized by a software program; the sensor type torque protection device combines the axial deformation of the first-stage worm of the electric actuator with the pressure sensor, and the voltage outputted by the pressure sensor is amplified by the circuit board, and then the signal is input to the signal By controlling the main board, the real-time torque value of the electric actuator can be obtained.

Torque protection refusal is mainly manifested in the AC power trip of the actuator, the severe wear of the worm gear of the electric actuator, the bending deformation of the door stem, and even the twisting of the electric actuator and the valve connecting screw. The torque protection value should be reset and the torque calibration table should be used. Check it out. When the valve torque is selected, it is necessary to ensure that the actuator reliably switches the valve, and the torque of the electric actuator cannot exceed the maximum torque that the valve stem can withstand. It is difficult to set the parameters because each valve stem can withstand The maximum torque is often not easy to obtain. The electric actuator manufacturers often use the torque parameter setting according to experience. First set the smaller torque protection value. If the torque protection action, increase the torque protection parameter setting until the valve is cold. The state can be normally opened and closed, and if the hot state is protected by the torque, the torque protection value is continuously increased to ensure that the valve can be normally opened and closed in the hot state.

2. 2 Torque protection malfunction
In the case of manual operation of the electric actuator, the over-torque protection action occurs. After the setting of the elimination torque protection value is too small, for the intelligent electric actuator, observe the liquid crystal torque value indication or the indicator light to display the over-torque information. When turning in the opposite direction, the original direction over torque signal should disappear. Otherwise, replace the main board or torque detection device and remove them one by one.
For the mechanical torque detecting device, the motor actuator is rotated in the opposite direction, and the check torque switch should be disconnected. Otherwise, the torque protection switch should be replaced; if the torque guarantee is set to the maximum value, the over-torque still occurs. Consideration should be given to whether the electric actuator is too small in torque selection.

3. The motor of the electric actuator rotates, and the output shaft of the actuator does not rotate. The specific reasons may be:
3. 1 The electric actuator is engaged on the manual side. After the motor of the electric actuator rotates, the switching device fails to engage to the motor side, causing the motor to idle.
3. 2 The worm gear driven by the electric actuator wears and slips, causing the motor to idle and the output shaft of the actuator does not rotate.
3. 3 The three-phase contact of the motor power line is unreliable, which causes the motor to not turn when it is turning.
For the electric actuator motor idling, after judging that the power supply has no fault, the electric actuator first stage worm gear box must be opened to check the worm gear wear condition. If the wear is serious, it can only be returned to the factory for repair, or replace the new electric actuator; Faults, according to the working principle of different electric actuator switching devices, can generally be repaired on site.

4, electric actuator motor overheating failure, the reasons may be:
4. 1 The electric actuator operates frequently, causing the motor to overheat and cause protection.
4. 2 The thermal resistance type temperature measuring component is disconnected or the terminal is in poor contact, and the generator overheating signal is incorrect.
4. 3 Motor rotor bearing damage can not be rotated, the motor is overheated due to motor stall.
If the bearing of the motor is damaged, the bearing should be replaced. When the temperature measuring component is damaged, the motor should be replaced. Because the temperature measuring component is replaced separately, the stator coil needs to be disassembled. The cost is too large and the cost is enough to purchase a new power of several hundred watts.

5. The electric actuators cannot be operated on the spot or in the distance. The reasons may be:
5. 1 The power board is faulty. The power board provides control power to the main board. If the power board is faulty, it may cause remote operation.
5. 2 The motherboard is faulty, which may result in the control command not being executed.
5. 3 Power failure, the electric device detects that the power supply is out of phase or has no power, and the electric actuator cannot operate.
For such faults, only replace the main board and the power board one by one, because the place of use does not generally have the conditions for testing the board.
6, electric actuators have no full open feedback, the reasons may be:
6. 1 The terminal position relay is faulty and cannot be reliably closed or opened.
6. 2 The relay settings are incorrect.
6. 3 motherboard failure.
When processing, first check the terminal position setting to ensure correct setting; for relay failure, if the position relay is installed separately, replace the position relay; if the position relay is soldered with the main board, replace the main board.

Shenzhen Power-Tomorrow Actuator Valve Co., Ltd is a high-tech enterprise of mechatronics. We have rich experience in the industry and are committed to solving all problems of users on valve electric devices.

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