Analysis of motor overheating

When the motor current is high, it often appears that the motor is generating heat. The following 7 points basically summarize the reasons for the high motor current.

 

First, the power problem

There are several reasons why the power supply overheats the motor:

 

1, the power supply voltage is too high

 

When the power supply voltage is too high, the motor back-EMF, flux, and flux density increase. Since the amount of iron loss is proportional to the square of the magnetic flux density, the iron loss increases, causing the core to overheat. The increase in the magnetic flux causes a drastic increase in the exciting current component, which results in an increase in stator winding copper loss and overheating of the windings. Therefore, if 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 electromagnetic torque of the motor remains unchanged, the magnetic flux will decrease, the rotor current will increase accordingly, and the load power component in the stator current will increase, causing the copper loss of the winding to increase, resulting in stator and rotor. Windings are overheated.

 

3, power supply voltage asymmetry

 

When one phase of the power line is disconnected, one fuse is blown, or the head blade of the blade starter burns, it will cause a three-phase motor to take a single phase, causing the running two-phase windings to overheat by the large current and to burn. Therefore, for three-phase motors, fuses are generally not suitable for protection.

 

4, three-phase power imbalance

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

From the above, it can be seen that when the motor is overheated, the cause of the power supply should be considered first (soft start, inverter, servo drive can also be considered as the power supply). After confirming that there is no problem with the power supply, consider other factors.

 

Second, the load problem

There are several reasons why the motor is overheated in terms of load:

 

1, the motor overload operation

When the equipment is not matched and the load power of the motor is greater than the rated power of the motor, the motor is overloaded for a long period of time (ie, a small horse-drawn cart), which may cause the motor to overheat. When servicing the overheated motor, it is necessary to find out whether the load power is consistent with the motor power to prevent blind and purposeless disassembly.

 

2, drag the mechanical load is not working properly

Although the equipment is matched, the dragged mechanical load is not working properly. When the load is running, the load is large and small, and the motor overloads and heats up.

 

3, drag the mechanical failure

When the machine being dragged is faulty, the rotation is not flexible or is stuck, the motor will be overloaded, causing the motor windings to overheat. Therefore, when the overhaul motor is overheated, the load factor cannot be ignored.

 

Third, the motor itself

1, the motor windings open circuit

When one phase winding breaks in the motor winding, or one branch breaks in the parallel branch, it will lead to unbalanced three-phase current and overheat the motor.

 

2, motor winding short circuit

When a short-circuit fault occurs in the motor windings, the short-circuit current is much larger than the normal operating current, which increases the winding copper loss, causing the windings to overheat and even burn.

 

3, motor star angle error

When the delta-connected motor is misconnected into a star, the motor still runs with full load. The current flowing through the stator winding exceeds the rated current, causing the motor to stop. If the stall time is longer and the power is not cut off, the winding is not only serious. Overheated, it will also burn. When the star-connected motors are incorrectly connected in a triangle, or if the motors of several coils grouped in a branch are mistakenly connected in two branches in parallel, the windings and cores will be overheated, and the windings will be burned in severe cases.

 

4, the motor coil connection error

When a coil, a coil group or a phase winding is reversed, it will lead to a serious imbalance of the three-phase currents, and the windings will overheat.

 

5, mechanical failure of the motor

When the motor shaft is bent, the assembly is not good, the bearing is defective, etc., the motor current will increase, and the copper loss and mechanical friction loss will increase, causing the motor to overheat.

 

 

Fourth, ventilation and heat problems

1, the ambient temperature is too high, so that the inlet air temperature is high.

 

2. The air inlet is blocked by the sundries, which makes the air intake slow, resulting in small air intake.

 

3, too much dust inside the motor, affecting heat dissipation.

 

4. The fan is damaged or reversed, causing no wind or small air volume.

 

5. The wind shield is not installed in the wind shield or the motor end cover, causing the motor to have no certain wind path.

 

Fifth, repair motor problems

 

The motor start-up current of the repaired motor reaches more than 66%. At the same time, frequent operation of the motor will also result in high current and overheating of the motor.

 

 

Sixth, series resistance problem

 

Winding motors and series resistors do not match. At the same time, frequent motor operation will also result in high current and overheating of the motor.

 

Seventh, motor vibration problem

Excessive motor vibration may also result in high motor current. Reasons and solutions:

1. Rotor imbalance - leveling balance

2. Pulley unbalance or shaft bending - check and correct

3, motor and load axis are not aligned - check the axis of the adjustment unit

4, the motor is not installed - check the installation and foot screws

5, suddenly overloaded load - reduce the load