When the motor current is high, it often manifests as severe motor overheating. The following five points summarize the reasons for excessive motor current. Let's learn about them.
Power supply problem
1. Power supply voltage is too high
When the power supply voltage is too high, the motor's back electromotive force, magnetic flux, and magnetic flux density all increase. Since the magnitude of iron loss is proportional to the square of the magnetic flux density, the increased iron loss leads to overheating of the iron core. The increased magnetic flux, in turn, causes a sharp increase in the excitation current component, resulting in increased copper losses in the stator windings and overheating of the windings. Therefore, when the power supply voltage exceeds the motor's rated voltage, the motor will overheat.
2. 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 supply component in the stator current will increase, resulting in increased copper losses in the windings and causing the stator and rotor windings to overheat.
3. Uneven power supply voltage
When one phase of the power supply line is broken, one phase of the fuse blows, or the switch starter is burned, causing one phase to be disconnected, a three-phase motor will run on only one phase. This will cause the two running windings to overheat due to high current, eventually burning out. Therefore, fuses are generally not used for protection of three-phase motors.
4. Three-phase power supply imbalance
When the three-phase power supply is unbalanced, it will cause the three-phase current of the motor to be unbalanced, resulting in overheating of the windings.
As can be seen from the above, when a motor overheats, the first thing to consider is the power supply (soft starters, frequency converters, and servo drives can also be considered power supply issues). After confirming that there are no problems with the power supply, other factors should then be considered.
Load issues
1. Motor overload operation
When equipment is incompatible, and the load power of the motor exceeds its rated power, the motor will operate under overload for a long time (i.e., a small motor pulling a heavy load), which will cause the motor to overheat. When repairing an overheated motor, it is essential to first determine whether the load power matches the motor power to prevent aimless disassembly.
2. The driven mechanical load is not working properly.
Although the equipment is compatible, the mechanical load it drives is not working properly. The load fluctuates during operation, and the motor is overloaded and overheats.
3. The driven machinery is malfunctioning.
When the driven machinery malfunctions, rotates inflexibly, or gets jammed, it will overload the motor, causing the motor windings to overheat. Therefore, when troubleshooting motor overheating, load-related factors cannot be ignored.
Problem with the motor itself
1. Open circuit in motor windings
When one phase of the motor winding is open-circuited, or when one of the parallel branches is open-circuited, it will cause an imbalance in the three-phase current, causing the motor to overheat.
2. Short circuit in motor windings
When a short circuit fault occurs in the motor winding, the short circuit current is much larger than the normal operating current, which increases the copper loss of the winding, causing the winding to overheat or even burn out.
3. Incorrect motor coil wiring
When a coil, coil group, or phase winding is reversed, it will cause a serious imbalance in the three-phase current, which will cause the winding to overheat.
4. Mechanical failure of the motor
When the motor shaft is bent, poorly assembled, or the bearings are faulty, the motor current will increase, copper loss and mechanical friction loss will increase, causing the motor to overheat.
ventilation and heat dissipation issues
1. The ambient temperature is too high, which causes the intake air temperature to be high.
2. Debris is blocking the air inlet, causing poor airflow and resulting in a small air volume.
3. Excessive dust inside the motor affects heat dissipation.
4. The fan is damaged or installed backwards, resulting in no airflow or low airflow.
5. The motor lacks a proper airflow path due to the absence of a fan cover or a baffle plate inside the motor end cover.
Excessive motor vibration can also cause high motor current. The causes and solutions are as follows:
Motor vibration problem
1. Rotor imbalance – Leveling and balancing
2. Uneven pulley or bent shaft extension – check and correct.
3. The motor and load axes are not aligned – check and adjust the unit's axes.
4. Improper motor installation – Check the installation details and base bolts.
5. Sudden overload – reduce the load.
Special Note: Some materials in this article are from the internet, and the copyright belongs to the original author.
