Common reasons for the serious heating of the screw air compressor motor

1. The air gap between the stator and rotor of the motor is very small, which may easily lead to collision between the stator and rotor

In medium and small motors, the air gap is generally 0.2mm to 1.5mm. When the air gap is large, the excitation current is required to be large, thereby affecting the power factor of the motor; if the air gap is too small, the rotor may rub or collide. Generally, due to the serious out-of-tolerance of the bearing and the wear and deformation of the inner hole of the end cover, the different axes of the machine base, end cover and rotor will cause bore sweeping, which will easily cause the motor to heat up or even burn out. If the bearing is found to be worn, it should be replaced in time, and the end cover should be replaced or brushed. The simpler treatment method is to inlay the end cover.

2. The abnormal vibration or noise of the motor can easily cause the motor to heat up

This situation belongs to the vibration caused by the motor itself, most of which are due to poor dynamic balance of the rotor, poor bearing, bent shaft, different shaft centers of the end cover, machine base, and rotor, loose fasteners, or uneven foundation of the motor installation, and improper installation It may be caused by the transmission from the mechanical end, which should be ruled out according to the specific situation.

3. If the bearing is not working properly, it will definitely cause the motor to overheat. Whether the bearing is working normally can be judged by hearing and temperature experience.

You can check the bearing end with your hands or a thermometer to determine whether its temperature is within the normal range; you can also use a listening rod (copper rod) to touch the bearing box. If you hear an impact sound, it means that one or several balls may be crushed. Hissing sound, it means that the lubricating oil of the bearing is insufficient, and the motor should change the lubricating grease every 3,000 hours to 5,000 hours.

4. The power supply voltage is too high, the excitation current increases, and the motor will overheat

Excessive voltage can compromise the motor insulation, putting it at risk of breakdown. When the power supply voltage is too low, the electromagnetic torque will decrease. If the load torque does not decrease and the rotor speed is too low, the increased slip will cause the motor to be overloaded and heat up. Long-term overload will affect the life of the motor. When the three-phase voltage is asymmetrical, that is, when the voltage of one phase is high or low, the current of a certain phase will be too large, and the motor will heat up. At the same time, the torque will decrease and the “humming” sound will be emitted. After a long time, the winding will be damaged.

In short, no matter whether the voltage is too high, too low or the voltage is asymmetrical, the current will increase, and the motor will heat up and damage the motor. Therefore, according to the national standard, the change of the power supply voltage of the motor should not exceed ±5% of the rated value, and the output power of the motor can maintain the rated value. The motor power supply voltage is not allowed to exceed ±10% of the rated value, and the difference between the three-phase power supply voltages should not exceed ±5% of the rated value.

5. Winding short circuit, turn-to-turn short circuit, phase-to-phase short circuit and winding open circuit

After the insulation between two adjacent wires in the winding is damaged, the two conductors touch each other, which is called winding short circuit. Winding short circuits that occur in the same winding are called turn-to-turn short circuits. A winding short circuit that occurs between two phase windings is called a phase-to-phase short circuit. No matter which one it is, it will increase the current of one phase or two phases, cause local heating, and age the insulation to damage the motor. Winding open circuit refers to the failure caused by the stator or rotor winding of the motor being broken or blown. Whether it is a short circuit or an open circuit of the winding, it may cause the motor to heat up or even burn out. Therefore, it must be shut down immediately after this happens.

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