The faults of asynchronous motors can be divided into mechanical faults and electrical faults. Mechanical faults such as bearings, iron cores, blades, bases, shafts, etc. are generally easier to observe and discover; electrical faults are mainly faults in the conductive parts such as stator windings and brushes. Due to the different types of construction, manufacturing quality, use and maintenance of the motor, it is often possible that the same fault has different appearance phenomena, or the same appearance phenomenon causes different faults. Therefore, in order to correctly judge the fault, careful and careful observation, research and analysis must be carried out. Then check and measure, find out where the fault is, and take appropriate measures to eliminate it.
Survey
First understand the model, specifications, operating conditions and service life of the motor, as well as the operation of the motor before the failure, such as the size of the load, the temperature rise, the abnormal sound, the operation, etc., and listen carefully. The operator's reflection.
2. Look at the fault phenomenon
The method of inspection should be flexibly controlled according to the motor fault condition. Sometimes the power supply on the motor can be operated for a short time, and the fault condition can be directly observed, and then the analysis and research can be carried out. Sometimes the motor can't be powered on, and it can be analyzed and judged by meter measurement or observation. Then the motor is disassembled, and the internal condition is measured and carefully observed to find out the fault.
3. Monitoring and maintenance of motor operation
When the motor is running, it is necessary to monitor the motor in time by listening, watching, smelling, etc., so that when the motor is abnormal, the power can be cut off in time to eliminate the fault. The specific items are as follows:
Listen to the sound of the motor when it is running. When the motor is running normally, the sound should be smooth, brisk, uniform, and rhythmic. If there is abnormal noise such as screaming, dullness, friction, impact, vibration, etc., stop the inspection immediately. Observe the motor for vibration, noise and abnormal odor
If the motor vibrates, it will cause the load part connected to it to increase in different degrees of heart, and the load on the motor will increase. When the load is overloaded, the motor will be burnt.
Check frequently through multiple channels. Check the temperature of the motor and the temperature of the bearing, stator, casing and other parts of the motor for abnormal changes. Especially for motors without voltage, current indication and without overload protection, monitoring the temperature rise is more important. If the motor bearing is overheated and lacks oil, if it is found that the temperature rise near the bearing is too high, it should be stopped immediately. Whether the bearing rolling element or the raceway surface is cracked, scratched or damaged, whether the bearing clearance is excessively shaken, and whether the inner ring rotates on the shaft or the like.
Keep the motor clean, especially the terminals and winding surfaces. Do not allow water droplets, oil and debris to fall on the motor, and let no debris or water droplets enter the motor.
unit. Regularly overhaul the motor, clean the inside, replace the oil, etc. When the motor is running, dust, water stains and other sundries are not allowed within at least 3 meters around the air inlet to prevent the inside of the motor from being attracted, forming a short-circuit medium, or damaging the wire insulation layer, causing short-circuit between turns, increasing current, and temperature. Raise and burn the motor.
It is necessary to measure the insulation resistance of the motor regularly, especially when the motor is wet, if it is found that the insulation resistance is too low, it should be dried in time.
For wound-wound motors, always pay attention to whether the spark between the brush and the slip ring is too large, such as excessive spark. It is necessary to do the cleaning work in time and carry out maintenance.
Keep the motor working at rated current
The main reason for the overload operation of the motor is due to the excessive load of the drag, the voltage being too low, or the mechanical jam caused by the drive. If the overload time is too long, the motor will absorb a large amount of active power from the power grid, the current will increase sharply, and the temperature will also rise. At high temperature, the insulation of the motor will age and burn out.
Check whether the three-phase current of the motor is balanced. The difference between the current of any one-phase current of the three-phase current and the average value of the other two-phase currents must not exceed 10%, so as to ensure the safe operation of the motor. If it exceeds, it indicates that the motor is faulty, and it is necessary to find out the cause and eliminate it in time.
The normal operation of the starting equipment and the technical state of the motor starting equipment play a decisive role in the normal starting of the motor. Practice has proved that the vast majority of burned motors are mostly caused by improper operation of the starting equipment. If the starting device has a phase loss start, the contactor contacts are arced, fired, etc. The maintenance of the starting equipment is mainly clean and fast. If the contactor contact is not clean, the contact resistance will increase, causing the heat to burn the contact, causing the phase loss and burning the motor; the core of the contactor suction coil is rusted and dusty, which will cause the coil to be loosely sucked and occurs. Strong noise, increase coil current, burn the coil and cause malfunction.
Symptoms Possible causes of malfunctions Remedy The motor cannot be started after the power is turned on. (1) The power is turned off or the power switch is not in good contact;
(2) The fuse is blown, and the wiring of the control equipment or the wiring of the secondary circuit is incorrect;
(3) The stator winding wiring is incorrect;
(4) The stator winding is broken, shorted or grounded, and the wound rotor of the wound motor is broken;
(5) The load is too heavy or the transmission machinery is faulty or the transmission mechanism is stuck;
(6) The rotor circuit of the winding motor is disconnected (poor contact between the brush and the slip ring, open circuit of the rheostat, poor contact of the leads, etc.);
(7) The power supply voltage is too low (1) Check the power supply, and the switch should be repaired or replaced if it is in poor contact;
(2) Replace the fuse, check the wiring of the control equipment or the secondary circuit wiring;
(3) Check wiring and correct errors;
(4) Identify the fault point and eliminate the fault;
(5) Check the transmission mechanism and load;
(6) Find out the break point and repair it;
(7) Check the cause and eliminate the excessive temperature rise or smoke of the motor (1) The load is too heavy or the start is too frequent;
(2) Phase failure operation of three-phase asynchronous motor;
(3) The stator winding wiring is incorrect;
(4) The stator winding is grounded or interturned, and the phase is shorted;
(5) Broken bar of squirrel cage motor;
(6) The winding motor windings are out of phase;
(7) the stator and the rotor are rubbed;
(8) poor ventilation;
(9) The power supply voltage is too high or too low (1) Reduce the load and reduce the number of starts;