The electric actuator is mainly composed of power board, main board, travel detection device, torque measuring device, AC contactor or frequency converter, motor and reducer. The electric actuator uses small motor to drive the worm gear and worm of the primary reduction mechanism, which can output multiple transfer motions, angular travel motions and straight travel motions to the valve. The motion output form of the electric actuator is determined by the characteristics of the controlled valve. If the working torque required by the controlled valve is especially large, such as more than 2000 NM, a secondary reduction gearbox is usually added, and the electric actuator directly drives the secondary reduction gearbox, and then the secondary reduction gearbox drives the valve movement; The protection of electric actuators usually includes valve position protection, torque protection, motor overheating protection, motor stall protection, control unit fault protection, power failure protection, etc. The fault treatment shall be targeted according to the alarm information of electric actuators.

1. Loss of valve position of electric actuator:

1.1 Loss of battery power

When the incremental encoder is used to measure the stroke, the actuator must have a battery as the auxiliary power supply. When the AC power supply disappears, the change of the valve position of the electric actuator can still be detected by the incremental encoder, and the full open and full close positions of the electric actuator will not change. If the AC power supply disappears, the battery power supply is exhausted. When the actual valve position of the electric actuator changes, the incremental encoder cannot detect the change of the valve position, As a result, the valve position is lost. When the AC power supply is restored again, the default valve position of some manufacturers is 50%; Now some manufacturers that use incremental encoders have improved their hardware by adding capacitance circuits. When the AC power supply disappears, they use capacitance to store electric energy to save the valve position. However, the electric actuator cannot be operated manually when there is no battery power supply, otherwise the valve position will still be lost. Therefore, when the battery power is low, replace the battery in time.

1.2 Hardware damage

The electric actuator encoder is disconnected, the encoder input voltage is too low, the travel transmission gear is damaged, the encoder circuit board is corroded, and the main board travel detection and storage components are damaged, which can lead to abnormal changes or loss of valve position. When handling, if the encoder input voltage is confirmed to be normal, replace the main board or the travel encoder one by one.

2. Torque fault of electric actuator:

2.1 Torque protection refuses to operate

To measure the output torque of electric actuators, there are mainly mechanical protection switches, motor current, voltage, power measurement and calculation torque, and sensor type protective devices: mechanical torque protection switches were widely used before 2000 and belong to a transitional product. Now some low-end electric actuators are still used. This torque protection switch can only provide switching value for torque protection, and cannot provide real-time data of process torque, The measurement error is large; To calculate torque by using motor current voltage and phase angle between current and voltage, software program is needed; The sensor type torque protection device combines the axial deformation of the primary worm of the electric actuator with the pressure sensor, amplifies the voltage output by the pressure sensor through the circuit board, and then inputs the signal to the control main board to obtain the real-time torque value of the electric actuator.

The refusal of torque protection is mainly manifested in the tripping of the AC power supply of the actuator, the serious wear of the worm gear and worm of the electric actuator, the bending deformation of the gate stem, and even the breaking of the connecting screws between the electric actuator and the valve. The torque protection value should be reset and verified with the torque verification platform. When selecting the valve torque, it is necessary to ensure that the actuator can reliably open and close the valve, and it is also required that 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 the maximum torque that each valve stem can withstand is often not easy to obtain. The manufacturers using electric actuators often set the torque parameters according to experience, and first set a smaller torque protection value, If the torque protection acts, increase the torque protection parameter setting appropriately until the valve can normally open and close in cold state. If the torque protection acts in hot state, continue to increase the torque protection value appropriately to ensure that the valve can normally open and close in hot state.

2.2 Moment protection maloperation

When the manual operation of the electric actuator is light, there is an over torque protection action. After the torque protection value is set too low, for the intelligent electric actuator, observe the LCD torque value prompt or the indicator light to display the over torque information. By turning in the opposite direction, the over torque signal in the original direction should disappear. Otherwise, replace the main board or torque detection device and eliminate them one by one.

For mechanical torque detection device, rotate the motor actuator in the opposite direction, check that the torque switch should be disconnected, otherwise, replace the torque protection switch; If the torque has been set to the maximum value by the torque protector and there is still excessive torque, it should be considered whether the torque of the electric actuator is too small.

3. The motor of the electric actuator rotates, but the output shaft of the actuator does not rotate. The specific reasons may be:

3.1 The electric actuator is engaged at the manual side. After the motor of the electric actuator rotates, the switching device fails to engage at the motor side, causing the motor to idle.

3.2 Worm gear and worm driven by electric actuator are worn and slipping, resulting in motor idling and actuator output spindle not rotating.

3.3 One of the three phases of the motor power line has unreliable contact, which causes the motor to rotate and not rotate.

For the motor of the electric actuator idling, after judging that there is no fault in the power supply, the primary worm gear box of the electric actuator must be opened to check the wear of the worm gear. If the wear is serious, it can only be returned to the factory for repair or replaced with a new electric actuator; The switching device failure can generally be repaired on site according to the working principle of switching devices of different electric actuators.

4. The motor of the electric actuator is overheated due to:

4. 1 The electric actuator operates frequently, causing the motor to overheat and causing protection action.

4.2 The thermal resistance type temperature measuring element is disconnected or the terminal is in poor contact, which causes the generator overheating signal to be incorrect.

4.3 The rotor bearing of the motor is damaged and cannot rotate, and the motor is overheated due to the locked rotor of the motor.

If the motor bearing is damaged, replace the bearing; When the temperature measuring element is damaged, the motor should be replaced, because the stator coil needs to be disassembled when the temperature measuring element is replaced separately, which is too expensive, and the cost is enough to purchase a new motor with power of hundreds of watts.

5. The electric actuator cannot be operated locally or remotely. The reasons may be:

5.1 If the power board fails, the power board provides control power to the motherboard. If the power board fails, remote and local operations may not be possible.

5.2 The mainboard is faulty, which may cause the control command to fail to execute.

5.3 In case of power failure, the electric actuator cannot operate when the electric device detects that the power supply lacks phase or no power supply.

Such faults can only be eliminated one by one by replacing the motherboard and power board, because the place of use generally does not have the conditions to test the circuit board.

6. The electric actuator has no feedback of full opening and closing, which may be caused by:

6.1 The terminal position relay fails and cannot be reliably closed or opened.

6.2 The relay is set incorrectly.

6.3 Main board failure.

When processing, first check the terminal position setting to ensure that the setting is correct; For relay failure, if the position relay is installed independently, replace the position relay; If the position relay is welded with the main board, replace the main board.

Conclusion:

The manufacturing technology of electric actuators in China was initially introduced from abroad. In the 1950s and 1960s, the electric actuators and valves were separated. The electric actuators indirectly controlled the valves through heavy transmission rods. The actuators had no torque protection and relied on motor protection to prevent over torque. Since the 1980s, the electric actuator has gradually formed an intelligent integration. The control unit, motor and reducer are installed together, and the electric actuator is directly installed on the valve. The control and protection have been greatly improved. Nowadays, the high-end electric actuator has adopted frequency conversion control technology, which makes the control more intelligent. The reliability of electric actuators mainly depends on the manufacturing level of main boards and power boards. For extremely important equipment, electric actuators imported from Germany and the United Kingdom are used in China, and the price is usually twice that of domestic electric actuators. In general, domestic electric actuators can be widely used. However, considering the reliability of electric actuators, it is recommended to use the electric actuators with absolute encoders. When the electric actuator uses an absolute encoder, regardless of whether there is AC power, the valve position of the electric actuator will not be lost, because each position of the actuator has a unique corresponding number. When the switch position of the actuator is confirmed, its absolute position will be stored in the permanent memory element. The electric actuator is powered on again, and the actual valve position can be read immediately, which greatly reduces the failure rate of the electric actuator.