1. The air gap between the stator and rotor of the motor is very small, which is easy to cause collision between the stator and the 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, the end cover and the rotor cause the sweeping, which can 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 insert a sleeve on the end cover.
2. The abnormal vibration or noise of the motor can easily cause the heating of the motor
This situation belongs to the vibration caused by the motor itself, most of which are due to the poor dynamic balance of the rotor, as well as poor bearings, bending of the rotating shaft, different axial centers of the end cover, machine base and rotor, loose fasteners or uneven motor installation foundation, and the installation is not in place. It may also be caused by the mechanical end, which should be excluded according to specific circumstances.
3. The bearing does not work properly, which will definitely cause the motor to heat up
Whether the bearing works normally can be judged by hearing and temperature experience. Use a hand or a thermometer to detect the bearing end 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 be replaced with grease every 3,000 to 5,000 hours of operation.
4. The power supply voltage is too high, the excitation current increases, and the motor will overheat
Excessive voltages can compromise the motor insulation, putting it at risk of breakdown. When the power supply voltage is too low, the electromagnetic torque will be reduced. If the load torque is not reduced and the rotor speed is too low, the increase of the slip ratio will cause the motor to overload and heat up, and the long-term overload will affect the life of the motor. When the three-phase voltage is asymmetric, that is, when the voltage of one phase is high or low, the current of a certain phase will be too large, the motor will heat up, and at the same time, the torque will be reduced, and a "humming" sound will be emitted, which will damage the winding for a long time.
In short, no matter 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 motor power supply voltage should not exceed ±5% of the rated value, and the motor output power 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 collide, which is called a winding short circuit. A winding short circuit that occurs in the same winding is called a turn-to-turn short circuit. A winding short circuit that occurs between two phase windings is called an interphase short circuit. No matter which one is, it will increase the current of one phase or two phases, cause local heating, and damage the motor due to insulation aging. Winding open circuit refers to the fault caused by the breaking or burning of the stator or rotor winding of the motor. Whether the winding is short-circuited or open-circuited, it may cause the motor to heat up or even burn. Therefore, it must be stopped immediately after this happens.
6. The material leaks into the inside of the motor, which reduces the insulation of the motor, thereby reducing the allowable temperature rise of the motor
Solid materials or dust entering the motor from the junction box will reach the air gap between the stator and rotor of the motor, causing the motor to sweep, until the insulation of the motor winding is worn out, causing the motor to be damaged or scrapped. If the liquid and gas medium leak into the motor, it will directly cause the motor insulation to drop and trip.
General liquid and gas leaks have the following manifestations:
(1) Leakage of various containers and conveying pipelines, leakage of pump body seals, flushing equipment and ground, etc.
(2) After the mechanical oil leaks, it enters the motor from the gap of the front bearing box.
(3) The oil seals such as the reducer connected to the motor are worn, and the mechanical lubricating oil enters along the motor shaft. After accumulating inside the motor, the motor insulating paint is dissolved, so that the insulation performance of the motor is gradually reduced.
7. Almost half of the motor burnout is caused by the lack of phase operation of the motor
The lack of phase often causes the motor to fail to run, or to rotate slowly after starting, or to generate a "humming" sound when the power is not rotating and the current increases. If the load on the shaft does not change, the motor is severely overloaded and the stator current will be 2 times the rated value or even higher. In a short time, the motor will heat up or even burn out. cause phase loss.
The main reasons are as follows:
(1) One-phase power failure caused by other equipment failures on the power line will cause other three-phase equipment connected to the line to operate without phase.
(2) One phase of the circuit breaker or contactor is out of phase due to burnout of bias voltage or poor contact.
(3) Phase loss due to aging, wear, etc. of the incoming line of the motor.
(4) The one-phase winding of the motor is open circuit, or the one-phase connector in the junction box is loose.
8. Other non-mechanical electrical failure causes
The temperature rise of the motor caused by other non-mechanical electrical faults may also lead to motor failure in severe cases. If the ambient temperature is high, the motor is missing a fan, the fan is incomplete, or the fan cover is missing. In this case, forced cooling must be ensured to ensure ventilation or replacement of fan blades, otherwise the normal operation of the motor cannot be guaranteed.
To sum up, in order to use the correct method to deal with motor faults, it is necessary to be familiar with the characteristics and causes of common motor faults, grasp the key factors, and conduct regular inspection and maintenance. In this way, we can avoid detours, save time, troubleshoot as soon as possible, and keep the motor in a normal operating state. So as to ensure the normal production of the workshop.
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