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What are the causes of AC MOTOR burnout?
Jul 24, 2018

There are many reasons for the AC MOTOR to burn out, and most of them can be prevented. Mainly due to the lack of phase and long-term overload operation, it may be due to bearing damage, moisture, blocking, end of service life, voltage instability is too high or too low.

Let's first look at the mechanical failure problem. The rotor of the AC MOTOR is fixed and flexible by the bearings at both ends. Then we must first ensure that it is operating normally. The most basic is that there is no shortage of lubrication. Therefore, it is necessary to add grease regularly. Small AC MOTORs without oil holes should be inspected from time to time. Butter and bearings. Once the bearing is damaged, it will cause the rotor to sweep, the end cover is worn, the abnormal sound is stuck, and the wire package is damaged and burned. At this point, stop and check and replace in time, and it is possible to recover the loss.

Next, let's take a look at the cause of the burnt electricity.

Missing phase. The lack of phase is the killer of a three-phase asynchronous AC MOTOR, and the general-purpose AC MOTOR is finished in ten minutes. The most terrible thing is the lack of phase of the entire power supply system, plus many of the equipment's switches are self-locking or automatically open (such as pumps, fans), after a power failure, the power transmission phase loss accident, may burn a dozen AC MOTORs . The best solution for a single AC MOTOR is to install an electronic phase loss protector (for important AC MOTORs). There is also the insurance in the three-phase circuit is also the cause of the lack of phase. Therefore, few people now install a fuse or the like in the main circuit of the three-phase AC MOTOR. A better method is to install a suitable circuit breaker.

overload. Overload is an important cause of high temperatures. If the protection function is normal (adding a suitable thermal relay), it usually does not happen. However, it should be noted that because the thermal relay can not be verified, and the protection value is not very accurate, the selection is not suitable, etc., and the artificial setting is automatically reset, so when protection is needed, it often does not work, and may also After many protections, the real reason was not found, and the protection value was artificially increased. To disable the protection.

Under normal circumstances, the AC MOTOR burned out by overload is completely black in the whole winding; the AC MOTOR that is burned out of phase is divided into two types: the delta connection method and the star connection method. The AC MOTOR connected to the phase is burned by the delta connection, and the coil only burns one phase ( 1/3), the star-connected AC MOTOR is two-phase (2/3).

The color of the AC MOTOR burned by overload is all black and black, and the phase burnout is (star connection) or (delta connection) winding black; the rest will be short circuit between turns, insulation damage, water inlet or foreign object Caused by a shot.

Get wet. The insulation performance caused by water ingress or damp is also a common cause of damage, but there is no way to protect it. Use only the attention and periodic shake insulation. Drying and re-dipping can be solved before burning. In particular, the AC MOTOR driven by the inverter should be careful of this item, otherwise the inverter may be burned.

Blocking: The AC MOTOR bearing is completely damaged and cannot be rotated to lock the AC MOTOR shaft, or the mechanical equipment dragged by the AC MOTOR is stuck, causing the AC MOTOR to stall. This causes the AC MOTOR to have a large stall current, causing the AC MOTOR winding temperature rise to rise sharply and burn. Bad AC MOTOR. Turn on the burnt AC MOTOR and check the stator windings. All the windings turn black.

high temperature. Continued work for a long time, causing the bearing to dry up, especially in the summer, the air temperature itself is high, coupled with the temperature generated by the AC MOTOR itself, in the slight negligence of the operator, it is easy to burn the AC MOTOR. Some of the AC MOTOR quality is not very good, in the detection of white embryos, it may not be closed, repair is not good, after immersing the paint and testing, there is no problem. Once the temperature rises, or is slightly damp, the insulation is reduced and the AC MOTOR is burned. There are many reasons for high temperature, overload, phase loss, excessive current, and so on. In this case, after the temperature of the AC MOTOR rises, its own insulation is reduced, which is another major cause of AC MOTOR burnout.

The end of the service life. All mechanical equipment has a service life, especially electrical equipment. During use, it will generate heat. When it is not in use, it will cool down. One cold and one heat is the main cause of insulation aging. It may appear after insulation aging. Problems such as phase-to-phase short circuit, turn-to-turn short circuit, and ground breakdown have inadvertently caused the AC MOTOR to burn out. The most important thing is to maintain and check frequently.

other. Others are not very common reasons, such as: the voltage is too low or too high, the vibration causes the terminal to loose the phase-to-phase short circuit, the pest damage, the imported AC MOTOR voltage does not match the domestic voltage (such as the Japanese AC MOTOR). Various types of decompression starting circuit failures cause no conversion, and the AC MOTOR works for a long time at low voltage.

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