Motor is an indispensable part of the electrical field, and its main function is to provide power. However, in the process of use, the motor often gets hot. Why? The following small series summarizes several common causes and solutions of motor heating, hoping to help you.
1. The abnormal operation of the bearing must cause the motor to heat up
Whether the bearing works normally can be judged by hearing and temperature experience.
The bearing end can be detected by hand or thermometer to judge whether its temperature is within the normal range; You can also use a listening rod (copper rod) to contact the bearing box. If you hear an impact sound, it means that one or several balls may be crushed. If you hear a hissing sound, it means that the lubricating oil of the bearing is insufficient. The motor should change the lubricating grease every 3000 ~ 5000 hours.
2. The power supply voltage is too high, the excitation current increases, and the motor will overheat
Excessive voltage will endanger the insulation of the motor and make it have the 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 slip will cause motor overload and heating, and long-term overload will affect the service life of the motor. When the three-phase voltage is asymmetric, that is, when the voltage of one phase is high or low, it will lead to excessive current of a phase, motor heating, and "buzzing" sound when the torque is reduced, which will damage the winding for a long time.
In short, whether the voltage is too high, too low or asymmetric, the current will increase, the motor will heat and damage the motor. Therefore, according to national standards, the change of motor power supply voltage shall not exceed ± 5% of the rated value, and the motor output power can maintain the rated value. The power supply voltage of the motor shall not exceed ± 10% of the rated value, and the difference between three-phase power supply voltages shall not exceed ± 5% of the rated value.
3. Abnormal vibration or noise of the motor is easy to cause heating of the motor
This situation belongs to the vibration caused by the motor itself. Most of it is caused by poor dynamic balance of the rotor, poor bearing, bending of the rotating shaft, different axis of the end cover, base and rotor, loose fasteners or uneven motor installation foundation and inadequate installation. It may also be transmitted from the mechanical end, which should be eliminated according to the specific situation.
4. The air gap between the stator and rotor of the motor is very small, which is easy to cause collision between the stator and rotor
In small and medium-sized motors, the air gap is generally 0.2mm ~ 1.5mm. When the air gap is large, the excitation current is required to be large, which affects the power factor of the motor; If the air gap is too small, the rotor may have friction or collision. 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 bore cleaning is caused by the different axes of the base, end cover and rotor, which is easy to heat or even burn the motor. If the bearing is found to be worn, it shall be replaced in time. The end cover shall be replaced or brush plated. The simpler treatment method is to insert the end cover.
5. Almost half of the motor burned out is caused by the lack of phase operation of the motor
The lack of phase often causes the motor to fail to run or rotate slowly after starting, or the rotation is weak, and the current increases with "buzzing" sound. If the load on the shaft does not change, the motor is in a serious overload state, and the stator current will reach twice or even higher than the rated value. The motor will heat up or even burn down in a short time. The main causes of phase loss operation are as follows:
If one phase of the power supply line is powered off due to the failure of other equipment, other three-phase equipment connected to the line will run without phase.
One phase of circuit breaker or contactor is out of phase due to burning of bias voltage or poor contact.
Phase loss of motor incoming line due to aging, wear and other reasons.
One phase winding of the motor is open circuit, or one phase connector in the junction box is loose.
6. The leakage of materials into the motor reduces the insulation of the motor, so as to reduce the allowable temperature rise of the motor
When solid materials or dust enter the motor from the junction box, it will reach the air gap between the motor stator and rotor, causing the motor to sweep the bore until the insulation of the motor winding is worn out, causing the motor to be damaged or scrapped. If liquid and gas media leak into the motor, it will directly cause the motor insulation to drop and trip. General liquid and gas leakage has the following forms:
Leakage of various containers and transmission pipelines, sealing leakage of pump body, flushing equipment and ground;
After the mechanical oil leaks, it enters the motor from the gap of the front bearing box;
The oil seals of the reducer connected to the motor are worn, and the mechanical lubricating oil enters along the motor shaft. After accumulating in the motor, the motor insulating paint is dissolved to gradually reduce the insulation performance of the motor.
7. Winding short circuit, turn to turn short circuit, phase to phase short circuit and winding open circuit
After the insulation between two adjacent conductors in the winding is damaged, the two conductors collide, which is called winding short circuit. The winding short circuit occurring in the same winding is called interturn short circuit. The winding short circuit between two-phase windings is called phase to phase short circuit. Either way, it will increase the current of one or two phases, cause local heating, aging insulation and damage the motor. Winding open circuit refers to the fault caused by the stator or rotor winding breaking or burning out of the motor. Whether the winding is short circuited or open circuited, the motor may be heated or even burned. Therefore, the machine must be shut down immediately after this happens.
8. Other non mechanical and electrical fault causes
The motor temperature rise caused by other non mechanical and electrical faults may also lead to motor failure in serious cases. If the ambient temperature is high, the motor lacks a fan, the fan is incomplete or the fan cover is missing. In this case, forced cooling is required to ensure ventilation or replace the fan blades, otherwise the normal operation of the motor cannot be guaranteed.
In order to adopt correct methods to deal with motor faults, we must be familiar with the characteristics and causes of common motor faults, grasp the key factors, and conduct regular inspection and maintenance, so as to avoid detours, save time, eliminate faults as soon as possible and make the motor in normal operation. So as to ensure the normal production of the workshop.