Common faults of AC motor and their causes

Common faults of AC motor and their causes

Ac motor in operation due to insulation, aging, friction, vibration and other reasons, failure is inevitable. If we can check, discover and eliminate these faults in time, we can effectively prevent the occurrence of accidents.

First, asynchronous motor fault inspection

1. Listen to the sound and locate the fault. Ac induction motor in operation, if you find a fine hum, there is no change of high and low, is a normal sound; On the contrary, if the sound is rough, and there is a sharp buzzing, sizzling sound is a precursor of failure, the following reasons should be considered:

(l) The iron core is loose, the vibration of the motor in operation, and the change of temperature will deform the fixed bolts of the iron core, resulting in the loosening of the silicon steel sheet and the production of large electromagnetic noise.

(2) Rotor noise The sound emitted by the rotor rotation, generated by the cooling fan, is a whining sound, like the knock of a drum, which is caused by the acceleration torque of the rotor core and shaft loosening in the case of sudden start, stop, reverse braking, etc., light can continue to use, heavy open inspection and repair.

(3) Bearing noise In the operation of the motor, we must pay attention to the culture of bearing sound, touch one end of the screwdriver on the bearing cover, the other end is attached to the ear, you can hear the sound changes inside the motor, different parts, different faults, there are different sounds. Such as crunch sound, is produced by the irregular movement of the rolling gun in the bearing, it is related to the clearance of the bearing and the grease state. The hiss is the sound of metal friction, which is generally caused by the lack of oil in the bearing, and the bearing should be disassembled and lubricated.

2. Using bromine sense, analyze that the faulty motor has no odor in normal operation; If you smell the ambiguity, it is a fault signal: such as burnt taste, it is emitted by the insulation barbecue, and with the increase of the motor temperature, it will smoke in serious cases; Such as the smell of oil coke, mostly the lack of oil bearing, in the near dry grinding state of oil and gas evaporation odor.

3. Use the feel to check the fault. Touch the shell of the TV with your hand, you can roughly judge the level of temperature rise, if you touch the motor shell with your hand will feel very hot, the temperature value is very high, you should check the cause, such as: overload, voltage is too high, and then troubleshoot the cause.

Second, the causes of common failures

1. The motor has no starting torque, or can not start when unloaded, and emits abnormal sound. Reasons: (l) three-phase power supply circuit (including knife switch, lead stator winding) has a phase off, resulting in single-phase start. (2) The power supply voltage is too low. (3) Excessive wear of the bearing makes the rotor close to one side of the stator, resulting in different hearts of the stator and the rotor and uneven air gap.

2. The motor starting torque is small, can not start when loaded, the load increases when the motor stops, sometimes emit a strong noise, local heat. Cause: low voltage of the power grid, short circuit between turns in the winding, broken line or welding phenomenon in the rotor winding, and single-phase operation caused by a phase broken line after starting.

3. The starting current is large, and unbalanced, and the sound is loud, causing the protection device to act and cut off the power supply. Cause: The wiring method of the stator winding may be incorrect, and the winding insulation to the ground is aging.