First, the power supply problem
1. The power supply voltage is too high
When the power supply voltage is too high, the motor back electromotive force, magnetic flux and magnetic flux density all increase. Since the magnitude of the iron loss is proportional to the square of the magnetic flux density, the iron loss increases, resulting in overheating of the core. The increase of magnetic flux leads to a sharp increase in the weight of the excitation current, which increases the copper loss of the stator winding and overheats the winding. As a result, when the supply voltage exceeds the rated voltage of the motor, the motor will overheat.
2. The power supply voltage is too low
When the power supply voltage is too low, if the electromagnetic torque of the motor remains unchanged, the magnetic flux will decrease, the rotor current will increase accordingly, and the weight of the load power supply in the stator current will increase accordingly, resulting in the overheating of the stator and rotor windings.
3. The power supply voltage is asymmetrical
When the one-phase power line is broken, the fuse is blown in one phase, or the corner head of the gate knife starting equipment is burned and the one-phase is not connected, the three-phase motor will be formed to go through the single phase, resulting in the running two-phase winding overheating through the high current, and even incineration. Therefore, fuses are generally not suitable for maintenance of three-phase motors.
4. The three-phase power supply is unbalanced
When the three-phase power supply is unbalanced, the three-phase current of the motor will be unbalanced, causing the windings to overheat.
From the above, it can be seen that when the motor overheats, the primary consideration should be the power supply (soft start, frequency converter, servo drive can also be regarded as the power supply). Once you have acknowledged that there is no problem with the power supply, you can consider the other aspects.
Second, the load problem
1. The motor is overloaded
When the equipment is not matched, and the load power of the motor is greater than the rated power of the motor, the motor will be overloaded for a long time (i.e., a small horse-drawn cart), which will lead to overheating of the motor. When repairing an overheated motor, it should be clear whether the load power is consistent with the motor power to prevent blind and purposeless disassembly.
2. The dragging mechanical load operation is abnormal
Although the equipment is matched, the dragged mechanical load is not normal, the load is large and small during operation, and the motor is overloaded and heated.
3. There is something wrong with the dragging machinery
When the dragged machinery has a fault, the rolling is not sensitive or it is stuck, it will overload the motor and cause the motor winding to overheat. Therefore, when overheating the motor, the load factor cannot be ignored.
Third, the motor itself problems
1. The motor winding is broken
When one of the windings of the motor is broken, or one of the branches of the parallel branch is broken, it will cause the three-phase current to be unbalanced and overheat the motor.
2. Short circuit in motor winding
When there is a short-circuit problem in the winding of the motor, the short-circuit current is much larger than the normal operating current, which increases the copper loss of the winding, resulting in overheating of the winding and even incineration.
3. The motor coil connection is wrong
When a coil, coil bank, or one-phase winding is reversed, it can cause a serious imbalance in the three-phase current, which can overheat the winding.
4. Mechanical problems of the motor
When the motor shaft is bent, the device is not good, and the bearing is faulty, etc., the motor current will increase, the copper loss and mechanical conflict loss will increase, and the motor will be overheated.
Fourth, ventilation and heat dissipation problems
1. The ambient temperature is too high, so that the air inlet temperature is high.
2. The air inlet is blocked by debris, which makes the air inlet not smooth and forms a small air intake.
3. There is too much dust inside the motor, which affects the heat dissipation.
4. The fan is damaged or reversed, resulting in no wind or small air volume.
5. The air shield is not installed or the wind shield is not installed in the end cover of the motor, forming a motor without a certain air path.
Excessive motor vibration may also cause high motor current, causes and treatment methods:
Fifth, the motor vibration problem
1. Rotor unbalance - leveling and balancing
2. The pulley is unbalanced or the shaft is stretched and bent - check and proofread
3. The axis of the motor and the load is not aligned - check the axis of the adjustment unit
4. Improper motor device - check the condition of the device and the foot screws
5. The load is suddenly too heavy - reduce the load
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