Several common faults and treatment methods for three-phase asynchronous motors:
First, the motor stator withstand voltage is not good
Experience has shown that the main reason for the poor compressive strength of the motor stator is due to defects in winding insulation, such as: cracking of the insulating bushing of the lead wire, bumping of the winding end, aging of the insulation between the phases, moisture of the motor, etc. Breakdown, so that the motor is burned.
Second, the motor no-load current is too large
The no-load current of the motor is related to factors such as the design of the magnetically permeable material and the manufacturing level, and also to the power and the number of poles of the motor. Under normal circumstances, the motor no-load current has a certain proportional relationship with the full load current. The power is small, the number of poles is large, and the ratio of no-load current to full-load current is large. The ratio of no-load current to full-load current of the Y series motor commonly used in the factory (%) ).
For the new motor or the motor after winding, the no-load current needs to be tested. If the measured no-load current of the motor exceeds the normal range, it indicates that there is a problem with the motor. The cause needs to be checked for processing. Table 2 lists the asynchronous motor no-load. The reason for the large current and the treatment method.
Third, the motor three-phase current imbalance
When the three-phase power supply is symmetrical, the three-phase no-load current of the asynchronous motor at the rated voltage, the deviation of any one phase from the average value shall not exceed 10% of the average value, only if the three-phase voltage imbalance is too large or the motor itself has In the event of a fault, the motor will generate a large three-phase current imbalance.
In addition to the three-phase current imbalance, the motor generates additional heat, which also causes the three-phase rotating magnetic field to be unbalanced, causing the motor to emit a special low-pitched sound, and the body vibrates accordingly. Table 3 shows the cause analysis of the three-phase current imbalance of the asynchronous motor.
Fourth, the motor temperature is high
When the motor is under normal operating conditions, its temperature should not exceed the temperature limit. The cause of overheating of the motor is very complicated. The abnormal situation of the power supply, the motor itself and the load will cause the motor to overheat. The poor ventilation and heat dissipation will also cause the motor to overheat. Figure 1 shows the cause and effect diagram of the motor overheating. If the motor overheats for a long time, the insulation of the motor will be aged and affected, which will affect the service life of the motor. If the temperature of the motor is high, it should be stopped to find out the cause and then use it.
Six, motor broom
When the motor rotates, the rotor rubs against the inner circle of the stator, which is called a motor broom. When the motor is broomed, scratches will appear on the outer surface of the rotor and the inner circle of the stator. This indicates that the rotor and stator gaps are not uniform. Severe brooms will cause high temperatures in the inner circumference of the stator. The insulation on the surface of the trough becomes brittle at high temperatures, causing the windings to be grounded or short-circuited, causing vibration and noise of the motor and degrading the performance of the motor. There are many reasons for causing a motor broom and they are intertwined.
Seven, motor bearing overheating
In small motors, ball bearings are generally used for the front and rear ends. In medium-sized motors, the roller bearings are generally used for the transmission end, the ball bearings are used at the other end, and the sliding bearing structure is also used. Bearing heating is the most common fault of asynchronous motors. The bearing heats up, and the lubricant is diluted and leaked out, and the bearing is damaged.
Eight, lack of phase operation
In daily work, phase loss operation is one of the common faults. As long as one phase disconnects in the three-phase power supply, the motor phase loss operation will occur. Phase loss operation may be caused by fuse blown fuses on the line, poor contact of the switch contacts or wire connectors. If the three-phase motor lacks a phase power supply, if it is in the stop state, it will be blocked due to the zero combined torque (cannot start). The stall current of the motor is much larger than the normal operating current, so in this case, the power-on time is too long or the power-on is frequently turned on several times, which will cause the motor to burn. When the running motor lacks one phase, if the load torque is small, the operation can be maintained. Only the rotation speed is slightly decreased, and an abnormal sound is emitted. When the load is heavy, the running time is too long, and the motor winding will be burnt.
