The life of a three-phase asynchronous motor depends mainly on the electrical, magnetic, thermal, vibration, environmental conditions and maintenance to which the motor is subjected during use. Usually, a motor can work for 15,000 to 80,000 hours under normal conditions . The main factors that affect the life of a motor are as follows : one is the subjective factor of a person; the second is the objective factor of the motor itself; and the third is the objective factor of the environment. 

1. Subjective factors of people

    Due to the difference in technical level of the personnel operating the motor , there may be unnecessary mistakes or errors when operating the motor, resulting in incorrect operation of the motor, such as frequent starting and heavy-load starting , which will cause damage to the motor and shorten its life.

2. Objective influence of the motor itself

2.1 Influence of load current fluctuations. If the motor circuit is frequently connected and switched, the load current will fluctuate frequently, causing the current to change sharply in a short period of time. This causes significant additional forces to be generated in the intercepting conductor, that is, the power supply line to the motor and the motor winding. These forces are related to the square of the current and act on the fixings, wrappings, rivets, supports, slot wedges, etc. through the insulating material of the current-carrying conductor. Over time, the insulation will be damaged and cause faults such as short circuits or open circuits, which will damage the windings and shorten the service life of the motor.

2.2 The influence of speed changes and fluctuations and reversal processes. These processes will generate additional mechanical forces in the insulated wires and act on the moving parts . At the same time, mechanical connectors, such as laminations and rotating shafts, will also generate additional loads, causing these moving parts and mechanical connectors to fatigue and age and lose their working ability.

2.3 The influence of thermal overload and temperature fluctuation. Thermal overload will damage the insulation material . Since the maximum temperature is directly related to the service life of the insulation material, the operating temperature of the motor is not allowed to exceed the maximum temperature allowed by the insulation material. Temperature fluctuation also affects the service life of the insulation material. The so-called temperature fluctuation refers to the temperature difference between the cold state and the hot state of the motor. When the motor is subjected to alternating loads, the above influence is particularly significant. Usually, temperature fluctuations will cause the wires, insulation layers and wrappings to expand , which can easily cause glue and paint and loosening, affecting the service life of the motor.

3. Objective factors affecting environmental conditions

   For example, marine motors, mining motors, and chemical industry motors all work in different harsh environmental conditions and are easily affected by the environment, which shortens their service life. For example, impure surrounding media or corrosive gases and high humidity will damage the electrical and mechanical properties of the motor. Therefore, when selecting a motor, you must select a motor with a corresponding protective structure based on the environmental conditions.

4 Conclusion

    Usually, if the capacity and installation form of the motor are reasonably selected, the service life of the motor will reach the designed service life, or even far exceed the designed service life. The factors that cause the shortened life of the motor can be summarized as follows: 1. The design temperature rise of the motor itself. If the design temperature rise of the motor is too high, and the ambient temperature exceeds the insulation limit temperature, the life of the motor will be greatly reduced. 2. Bearings. Poor bearing quality and short life will lead to short motor life. Mainly after a mechanical failure, the stator and rotor will rub against each other, damage the stator winding, and affect the life of the motor. 3. Insulation materials. The quality of the insulation material is poor, and the temperature limit of the motor is reduced. 4. The quality of the external power supply is poor, the power supply voltage is too high or too low, the harmonics are high, and the insulation is impacted, which will affect the life of the motor. 5. Environmental conditions and working conditions. The ambient temperature is too high or too low, and there is too much dust on site, which will reduce the insulation performance and shorten the bearing life.

    Generally speaking, the life of the motor is greater than or equal to the life of the winding and greater than or equal to the life of the bearing . To ensure the life of the motor, the following aspects should be noted during the use and maintenance of the motor: 1 ) Ensure that the motor is well lubricated during operation. 2 ) The operating environment should always be kept dry, the surface of the motor should be kept clean, and the air inlet should not be blocked by dust, fibers, etc. 3 ) When the thermal protection of the motor is continuously activated, it should be found out whether the fault is caused by the motor or the overload or the setting value of the protection device is too low. Only after the fault is eliminated can it be put into operation again. 4 ) When replacing the winding, the form, size, number of turns, wire gauge, etc. of the original winding must be recorded. When these data are lost, they should be obtained from the manufacturer. Randomly changing the original design winding often deteriorates one or several performances of the motor, and even makes it unusable. 5 ) When disassembling the motor, it is OK to remove the rotor from the shaft extension end or the non-extension end. If there is no need to remove the fan, it is more convenient to remove the rotor from the non-shaft extension end. When pulling the rotor out of the stator, it should be prevented from damaging the stator winding or insulation. 6 ) When the vibration and noise of the motor increase significantly, the radial clearance value of the bearing should be checked. If the inspection result indicates that the bearing has reached the end of its life, the bearing should be replaced in time.

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