When the motor current is high, it is often manifested in the severe heat generated by the motor. The following 7 points basically summarize the reasons for the motor current too high. Let us learn it.
1. Power supply problem
. The reasons for overheating of the motor in terms of power supply are as follows:
1. The power supply voltage is too high
. When the power supply voltage is too high, the back electromotive force , magnetic flux and flux density will increase accordingly. Since the magnitude of iron loss is proportional to the square of the magnetic flux density, the iron loss increases, causing iron core to overheat. The increase in magnetic flux causes the excitation current component to increase sharply, causing the copper loss of the stator winding to increase, causing the winding to overheat. Therefore, when the power 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 motor's electromagnetic torque remains unchanged, the magnetic flux will decrease, the rotor current will increase accordingly, and the load power component in the stator current will increase accordingly, causing the copper loss of the winding to increase, causing the stator and rotor windings to overheat.
3. Power supply voltage is asymmetric
When one phase of the power line is broken, the fuse is blown in one phase, or the angle head of the brake knife starter device is burned, causing one phase to block, it will cause the three-phase motor to go single phase, causing the running two-phase winding to overheat through a large current and burn. Therefore, fuses are generally not suitable for protection for three-phase motors .
4, three-phase power supply imbalance
When the three-phase power supply is unbalanced, the three-phase current of the motor will be unbalanced, causing the winding to overheat.
As can be seen from the above, when the motor overheats, the power supply reasons should be considered first (soft start, inverter, and servo drive can also be regarded as power supply). After confirming that there is no problem with the power supply, consider other factors.
2. Load problem
Load aspect
There are several reasons for overheating of the motor:
1. Overload operation of the motor
When the equipment is not equipped 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 pulls a big cart), which will cause the motor to overheat. When repairing an overheated motor, you should first find out whether the load power matches the motor power to prevent blind and purposeless disassembly.
2. The dragged mechanical load is not working properly
Although the equipment is equipped, the dragged mechanical load is not working properly. The load is large and small during operation, and the motor is overloaded and heated.
3. The dragged machine has a fault
When the dragged machine has a fault, inflexible rotation or is stuck, it will overload the motor and cause the motor winding to overheat. Therefore, when the maintenance motor is overheated, load factors cannot be ignored.
3. Problems of the motor itself
1. Motor winding break
When one phase winding breaks in the motor winding, or one branch in the parallel branch is broken, it will cause the three-phase current to be imbalanced and cause the motor to overheat.
2, motor winding short circuit
When the motor winding has a short circuit fault, the short circuit current is much greater than the normal working current, which increases the copper loss of the winding, causing the winding to overheat and even burn.
3. Motor star angle connection method error
When the triangular connection method motor is misconnected into a star, the motor is still running with full load, the current flowing through the stator winding exceeds the rated current, and even causes the motor to stop by itself. If the stop time is a little longer and the power supply is not cut off, the winding will not only overheat, but will also burn. When the motor connected to star is misconnected into a triangle, or the motor connected into a branch is misconnected into two branches in parallel, it will overheat the winding and the core, and in severe cases it will burn the winding.
4. Motor coil connection method error
When a coil, coil group or one-phase winding is connected in reverse, it will cause serious imbalance of the three-phase current and overheat the winding.
5, mechanical failure of the motor
When the motor shaft is bent, poorly assembled, and bearing problems, it will increase the motor current, copper loss and mechanical friction loss, causing the motor to overheat.
4. Ventilation and heat dissipation problem
1. The ambient temperature is too high, making the inlet air temperature high.
2. There is debris blocking the air inlet, causing the air inlet to be poor and causing the air inlet to be small.
3. Too much dust inside the motor affects heat dissipation.
4. The fan is damaged or installed in reverse, resulting in no wind or small air volume.
5. No air hood is installed or no wind shield is installed in the end cover of the motor, resulting in no certain air path for the motor.
5. Repair motor problem
The repaired motor start current reaches more than 66%. At the same time, the motor is frequently operated, which will also cause high current and overheating of the motor.
6. Series resistance problem
Winding motor does not match series resistors, etc. At the same time, the motor is frequently operated, which will also cause high current and overheating of the motor.
7. Motor vibration problem
Excessive vibration of motor may also cause high motor current. Causes and treatment methods:
1, rotor imbalance ——Calibration balance
2, pulley imbalance or shaft extension bending ——Calibration and correction
3, motor and load axis are not connected Align - Check and adjust the axis of the unit
4, motor installation is inappropriate - Check the installation status and foot screws
5, load suddenly is too heavy - Reduce the load
Source: Internet, delete
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