Due to its simple structure and high operating efficiency, three-phase asynchronous motors have been widely used in various fields of the national economy and play an important role. However, the failure rate of electric motors is relatively high, and accidents of motor burnout often occur and are on the rise, seriously affecting production quality.
After observation and analysis, it is concluded that motor failures are rarely caused by the quality of the motor itself, and the vast majority of failures are caused by environmental influences and improper maintenance during operation. Below is a brief discussion on the causes and treatment methods of local burnout of three-phase asynchronous motor windings.
1. Due to the unsuitable quality or form of the motor itself and the environment, as well as the pollution of liquids or gases such as acids, alkalis, salts, etc. in the environment, water or other harmful liquids enter the interior of the motor, causing the insulation of the motor winding to be corroded, resulting in a short circuit of the winding coil to ground, or between phases, or between turns, leading to local damage to the motor winding.
Handling method:
(1) Choose motors with good quality, especially selecting a reasonable motor form based on the working environment. In environments with harmful liquids or gases, choose sealed motors. In flammable and explosive environments, choose dust-proof and explosion-proof motors.
(2) Pay attention to sealing every part of the motor during maintenance and repair. Protective covers or sealant should be applied to areas where the motor is prone to leakage, immersion in liquids or dirt.
(3) Try to improve the working environment as much as possible and avoid the occurrence of running, emitting, dripping, and leaking of production processes and equipment.
(4) Motors operating in harsh environments should shorten the cycle of minor and medium repairs, and strengthen maintenance and upkeep regularly.
2. Due to bearing damage and deformation of the shaft, friction between the stator and rotor (commonly known as sweeping the bore) causes a sharp rise in the temperature of the iron core, burning out the slot insulation and inter turn insulation, resulting in short circuits to ground or inter turn short circuits in the winding coils, causing blasting. In severe cases, it can cause deformation of the stator iron core, wear and tear of the shaft, and scrap of the end cover.
The reasons for bearing damage are generally caused by the following reasons:
(1) Improper assembly of bearings, such as uneven tapping of the bearing inner ring during cold installation, can damage the shaft, causing the bearing inner ring to lose interference fit with the shaft or the interference fit to decrease, resulting in running of the inner ring. Uneven tapping during installation of the motor end cover can cause the bearing chamber and outer ring of the end cover to become too loose and run of the outer ring. Whether running on the outer or inner ring, it will cause a sharp increase in the operating temperature of the bearing, leading to overheating and burning of the winding.
(2) When cleaning bearings, or if the grease added is not clean, there may be tiny rigid substances left in the cavity, which can cause damage to the bearing passage during operation and result in temperature rise and bearing burnout.
(3) After the motor was repaired, the precision of the shaft machining was insufficient for the stator and rotor, resulting in the inner and outer rings of the bearing not being on the same plane, causing the bearing to run unevenly and resulting in an increase in temperature until it burned out.
(4) The motor runs for a long time, and the operating temperature of the body rises. The lubricating grease of the bearings is not replenished in time, causing dry wear of the bearings, and the temperature rises until it burns out.
In addition, the motor may be damaged due to the mixing of different oils and fats, quality issues with the bearings themselves, long-term disuse, and deterioration of the oils and fats.
Handling method:
(1) When disassembling bearings, try to heat the bearings to 80-100 ℃, such as using bearing heaters, transformer oil boiling, etc., in order to ensure the assembly quality of the bearings.
(2) Before installing the bearing, the cleaning work should be careful and meticulous, and no impurities should be left in the bearing chamber. The grease added should also be kept clean.
(3) In motor maintenance, it is generally not advisable to easily process the shaft and end cover, as it is difficult for non-specific personnel to achieve the original accuracy of the motor.
(4) When assembling the motor, it is necessary to ensure that the stator and rotor iron cores are aligned and not misaligned.
(5) The stator casing should be clean, free of debris, and ensure good ventilation channels.
(6) For motors that have been out of use for a long time, necessary disassembly inspections and replacement of bearing grease are required when they are put into use.
3. Due to the long end of the motor winding, it is prone to damage during maintenance and operation, resulting in local burnout of the winding.
Solution: During maintenance or repair, be sure to protect the end of the winding. When extracting the core of the motor rotor, it is necessary to lift the rotor to avoid friction between the stator and rotor cores. Before reinstalling the motor, it is necessary to carefully inspect the winding coils.
4. Due to long-term overload or overheating operation, the aging of winding insulation accelerates, and weak insulation points can cause inter turn short circuits, inter phase short circuits, or ground short circuits, resulting in local burnout of the winding.
Handling method:
(1) Try to avoid motor overload or overheating operation as much as possible. Check the cause of overload, if there is mechanical jamming, try to eliminate it; If the motor and load do not match, it is necessary to replace the motor with a higher power level.
(2) Ensure that the motor casing has clean ventilation channels;
(3) Ensure that there are good fans and blades, and replace damaged ones in a timely manner.
(4) Try to avoid frequent starting of the motor.
5. The insulation of motor windings is affected by mechanical vibrations (such as the impact of high currents during start-up, vibrations of dragged mechanical equipment, imbalance of motor rotors, etc.), which can cause adverse phenomena such as inter turn looseness and insulation cracks in the windings. The destructive effect continues to accumulate, and thermal expansion and contraction cause friction on the winding, accelerating insulation aging and leading to local burnout of the winding.
Handling method:
(1) Try to avoid frequent starting of the motor, and use soft starting for high-power motors to reduce the impact of starting current.
(2) Ensure that the vibration of the dragged mechanical equipment is within the specified range.
(3) Motors operating under vibration conditions should shorten the time for minor and medium repairs, and regularly check the insulation of the motor windings. The research and development, production, and sales of motor collection pump motors are integrated. The production plant covers an area of 46000 square meters and is equipped with automated CNC equipment, with an annual production capacity of 200000 units, providing faster supply. Our own type testing center, complete quality assurance system, procurement control system, modern management system, and comprehensive product performance and quality win.