When the motor current is high, it often manifests as severe heating of the motor. The following 7 points basically summarize the reasons for high motor current. Let's learn about them.

Power issue

There are several reasons for the motor to overheat in terms of power supply:

1. The power supply voltage is too high

When the power supply voltage is too high, the back electromotive force, magnetic flux, and magnetic flux density of the motor all increase accordingly. Due to the fact that the magnitude of iron loss is proportional to the square of magnetic flux density, the iron loss increases, leading to overheating of the iron core. And the increase in magnetic flux leads to a sharp increase in the excitation current component, causing an increase in copper loss in the stator winding and overheating of the winding. Therefore, when the power supply voltage exceeds the rated voltage of the motor, it will cause the motor to 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 constant, the magnetic flux will decrease, the rotor current will increase accordingly, and the load power component in the stator current will increase, causing an increase in copper loss in the winding and overheating of the stator and rotor windings.

3. Asymmetric power supply voltage

When one phase of the power cord is broken, one phase of the fuse is blown, or the corner of the switch starting equipment is burned, causing one phase to not be connected, it will cause the three-phase motor to run single-phase, causing the two-phase winding to overheat and even burn out due to high current. Therefore, fuses are generally not suitable for protecting three-phase motors.

4. Unbalanced three-phase power supply

When the three-phase power supply is unbalanced, it will cause the three-phase current of the motor to be unbalanced, causing the winding to overheat.

As can be seen from the above, when the motor overheats, the power supply should be considered first (soft start, frequency converter, servo drive can also be considered as power supply). After confirming that there are no issues with the power supply, consider other factors.

Load issue

There are several reasons for motor overheating in terms of load:

1. Overload operation of electric motor

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 operate under overload for a long time (i.e. a small horse pulling a large car), which will cause the motor to overheat. When repairing an overheated motor, it is necessary to first determine whether the load power matches the motor power to prevent blind and aimless disassembly.

2. The mechanical load being dragged is not functioning properly

Although the equipment is matched, the mechanical load it drags is not working properly. During operation, the load varies greatly, and the motor is overloaded and generates heat.

3. The dragging mechanism is malfunctioning

When the dragged machinery malfunctions, rotates inflexibly or gets stuck, it will overload the motor and cause the motor winding to overheat. Therefore, when repairing motor overheating, the load factor cannot be ignored.

Problems with the motor itself

1. Open circuit of motor winding

When one phase of the motor winding is broken or one branch of the parallel branch is broken, it will cause three-phase current imbalance and cause the motor to overheat.

2. Short circuit of motor winding

When a short circuit fault occurs in the motor winding, the short-circuit current is much higher than the normal operating current, which increases the copper loss of the winding, causing it to overheat or even burn out.

3. Error in star angle connection of electric motor

When the delta connected motor is misconnected into a star shape, the motor still runs at full load, and the current flowing through the stator winding will exceed the rated current, even causing the motor to stop on its own. If the stopping time is slightly longer and the power is not cut off, the winding will not only overheat severely, but also burn out. When a star connected motor is misconnected into a triangle, or when several coil groups are connected in series as one branch of the motor are misconnected into two parallel branches, it will cause the winding and iron core to overheat, and in severe cases, it will burn out the winding.

4. Wrong connection of motor coil

When a coil, coil group or phase winding group is connected in reverse, it will cause serious imbalance of three-phase current and cause overheating of the winding.

5. Mechanical failure of electric motor

When the motor shaft is bent, poorly assembled, or the bearings have problems, it will increase the motor current, copper loss, and mechanical friction loss, causing the motor to overheat.

Ventilation and heat dissipation issues

1. The ambient temperature is too high, causing the inlet air temperature to be high.

2. There are debris blocking the air inlet, causing poor air flow and resulting in low air intake.

3. Excessive dust inside the motor affects heat dissipation.

4. The fan is damaged or installed backwards, resulting in no wind or low air volume.

5. Failure to install a wind cover or wind deflector inside the motor end cover results in the motor not having a certain air path.

Repair motor issues

The starting current of the repaired motor exceeds 66%, and frequent motor operation can also cause high current and overheating of the motor.

Series resistance issue

The mismatch between wound motor and series resistor, as well as frequent operation of the motor, can also cause high current and overheating of the motor.

Vibration problem of electric motor

Excessive vibration of the motor may also cause high motor current. Reasons and solutions:

1. Rotor unbalance - leveling balance

2. Unbalanced pulley or bent shaft - check and correct

3. Motor and load axis are not aligned - check and adjust the axis of the unit

4. Improper installation of electric motor - check installation condition and foot screws

5. Sudden overload - reduce the load