One is mechanical failure, such as excessive load, bearing damage, rotor scan boring (friction between the outer circle of the rotor and the inner wall of the stator), etc.; the other is electrical failure, such as winding open circuit or short circuit. The fault phenomenon of three-phase asynchronous motors is more complicated. The same fault may have different phenomena, and the same phenomenon may be caused by different reasons. When the motor fails, if the cause is unknown, you can check it as follows. 1) The general inspection sequence is external first, internal second, mechanical first, electrical first, control part first, then unit part, using the method of "asking, seeing, hearing, smelling and touching". 2) Check whether the three-phase power supply has power. 3) Check whether the power switch and control circuit are faulty, such as whether the wiring and fuse are intact, etc., use an electric pen or multimeter to determine whether the three-phase power is symmetrical, whether there is a lack of phase or virtual connection, and whether the voltage is undervoltage, etc. 4) Check whether the motor load is normal, whether there are mechanical jams, excessive load, insufficient power grid capacity, etc. Under the normal condition of the three-phase power supply, the simple way to determine whether there is a problem with the load is to remove the motor load, let the motor run without load, listen to the sound, smell the smell, touch the motor shell with your hand, and test its heating. If everything is normal for the motor, it can basically be determined that there is a problem with the load of the motor. If the motor heats up quickly, even emits smoke, or makes an abnormal sound when it is energized, the power should be cut off immediately for inspection. 5) When checking the fault of the motor itself, first open the junction box to check whether there is a wiring error, disconnection, U-turn or burnt phenomenon. 6) Observe whether there are any abnormalities on the surface of the motor, and whether there are any cracks in the end cover and casing. Swing the shaft by hand to observe whether there is any shaft shifting phenomenon; rotate the shaft by hand to observe whether the rotation is flexible, whether there are boring and bearing problems. If the sound is abnormal, check whether the lubricating oil is dry, whether the bearing is damaged or missing, etc. 7) If it is difficult to determine the cause of the failure by surface observation, you can use the meter to measure. Disassemble the motor, use a megger to measure the insulation resistance between the phases of the windings and the insulation resistance to the ground respectively, and check whether the stator windings are disconnected, burned, short-circuited between phases, or short-circuited to the shell. Generally, after the motor fails and heats up, you can smell burnt smell when disassembling the motor, and the winding insulation layer may change color or even have obvious burn marks. Generally, small motors need to rewind the windings. Medium-sized motors can be partially replaced or completely rewinded depending on the degree of damage . If the insulation resistance meets the requirements, use a bridge to measure whether the DC resistance of the three-phase windings is balanced. 8) Check the rotor and shaft. If there is no obvious problem, check whether the cage bar and end ring are broken.