Troubleshooting methods for three-phase asynchronous motors

Common faults of three-phase asynchronous motors, including faults occurring at starting, faults occurring during operation, the motor cannot start without any sound, the motor cannot start with a humming sound, unbalanced three-phase power supply to the motor and temperature rise or even smoke, and other common fault diagnosis and troubleshooting methods.

Troubleshooting methods for three-phase asynchronous motors

For a motor to operate normally, its voltage, current, temperature rise and speed should all remain within the rated range.

There should be no violent vibration or abnormal noise during operation. If the motor does not operate normally, abnormal phenomena will inevitably occur, such as excessive current, excessive temperature rise or vibration, or even smoke and odor.

The reasons for abnormal operation of the motor include power supply and load, as well as poor operating environment, improper installation, and poor maintenance. In addition, when the motor itself fails, it may also cause operating failures.

The fault phenomena caused by different reasons are often similar, so correctly analyzing the cause of motor operation failure is a complex and meticulous task, and it plays an important role in timely troubleshooting.

After a motor failure occurs, the first thing to do is to conduct a thorough investigation and study. We must carefully listen to the feedback of the on-duty personnel who use this motor, as well as the operation of the motor before the failure, such as the size of the load, the temperature rise, and whether there is any sound, etc. Secondly, we must carefully observe the fault phenomenon, such as observing the current, voltage, power, sound, speed, vibration, temperature rise, and whether there is a burning smell, heat, smoke, etc.

There are many ways to observe. Sometimes you can connect the motor to a three-phase power supply to directly observe all the phenomena and then analyze them. (Electrician's World www.dgjs123.com) If it is not appropriate to connect the power supply, you can disassemble the motor and observe the internal conditions.

Finally, based on the investigation, research and observation of phenomena, analysis and judgment are carried out according to basic theories and work experience, and the possible causes of the failure are determined from the main phenomena of the failure.

On the basis of preliminary analysis, further investigation, observation or necessary tests and measurements can determine the cause of the fault and the location of the damage. There are two types of common motor operating faults: one is the fault that occurs during starting, and the other is the fault that occurs during operation.

1. Faults that occur when starting a three-phase asynchronous motor

1. The motor cannot start and there is no sound

First check whether the fuse is blown, then check whether the switch, starting device and motor winding have poor contact or circuit break. If the fuse is blown in two or more phases, the fuse should be replaced; if the switch or starting device has poor contact in two or more phases, the poor contact should be checked and repaired; if the Y-connected motor winding has two or three phase circuit break, or the △-connected motor winding has three phase circuit break, the fault point should be found and repaired.

2. The motor cannot start and there is a buzzing sound

First check whether the fuse is blown, then check whether the switch and starting device have poor contact, and finally check whether the motor winding is broken. If one phase of the fuse is blown, the fuse should be replaced; if one phase of the switch or starting device is broken or has poor contact, the poor contact should be checked and repaired; if one phase of the Y-connected motor winding is broken, or one or two phases of the △-connected motor winding are broken, the fault point should be found and repaired; if the power supply voltage is too low, the cause of the low voltage should be found, and the voltage should be adjusted or restored before working.

3. The motor cannot start and the fuse is blown

When the switch is pushed, the fuse explodes, which is mostly caused by the reverse connection of one phase or the Y connection mistakenly connected to the △ connection, as well as the short circuit of the winding and the grounding fault. When checking, you should first consider whether the fuse is too small, whether the connection method and operation are correct, and then check whether the transmission device and the load machine are stuck, as well as the load size. When checking, separate the motor and the load machine. If the motor can start normally, check the towed machine to eliminate the fault.

When one side of the stator winding is connected in reverse, the three phases should be distinguished and connected correctly; when the stator winding has a grounding or short circuit fault, the winding short circuit and grounding points should be checked and repaired; if the wiring is wrong and the Y-connected motor is connected as a △, it should be connected again; when the starting device is improperly operated, the starting device should be checked; when the load is too large, the load should be checked; when the load machinery is stuck or the transmission machinery has a fault, the load machinery transmission device should be checked; when the stator and rotor rub against each other, the cause of the rubbing should be found out and repaired; when the fuse is too small, a reasonable fuse should be selected.

4. The motor is difficult to start and the speed is low

First, check whether the connection method is consistent with the nameplate, then check whether the load and power supply voltage are normal, and finally check the stator winding and rotor faults.

When the power supply voltage is too low, the voltage should be adjusted or restarted when the voltage is normal; if the motor is connected incorrectly and the △-connected motor is connected as y-connected, it should be corrected according to the correct connection method; when one phase winding of the triangle-connected motor is broken, the break should be checked and repaired; when the cage rotor bars or end rings are broken, the aluminum should be recast or a new rotor should be replaced; when the motor is overloaded, the load should be reduced.

2. Faults that occur when a three-phase asynchronous motor is running

1. The three-phase power supply of the motor is unbalanced and the temperature rises or even smokes.

First check whether the fuse, switch power cord and connector have poor contact, then check whether the power supply voltage is broken, and finally check whether the winding is broken, grounded or connected incorrectly. If the coil is not replaced and it has been running normally in the past, there is no need to check whether the winding is connected incorrectly.

When the power supply voltage is unbalanced, the cause of the line voltage imbalance should be investigated and eliminated; when there is a short circuit or grounding fault in the motor winding, the short-circuit grounding point should be checked and repaired; after replacing the coil, if some coils are connected incorrectly, the wrong connection should be found and corrected; when the motor winding is broken, the breaking point should be found and reconnected.

2. The three-phase current of the motor increases at the same time, the temperature is too high and even smoke occurs

First check whether the wiring of the stator winding is consistent with the nameplate, then check whether the line voltage is normal, and finally adjust the load to check the towed machinery.

When the power supply voltage is too high or too low, the line voltage should be adjusted or the voltage should be normal before working again; when the motor is overloaded, the load should be reduced; when the towed machinery fails, the load machinery and transmission device should be checked; when the motor winding is connected incorrectly, it should be changed.

3. The current does not exceed the rated value, but the temperature is too high

Check the following items separately: When the ambient temperature is too high, try to lower the ambient temperature or reduce the motor's usage capacity; when ventilation is not smooth, clean the air duct or move away things that affect ventilation; too much dust and sludge on the motor affects heat dissipation, so the dust and sludge should be removed.

4. Abnormal vibration of the motor

First, determine whether the fault is a mechanical fault or an electrical fault. The method of judgment is: if the motor vibrates when the power is turned on and the motor vibrates when the power is turned off, it is a mechanical fault; if there is vibration when the power is turned on and the vibration disappears when the power is turned off, it is an electrical fault.

For mechanical aspects, perform the following five inspections: When the motor foundation is unstable or poorly calibrated, the foundation should be reinforced or recalibrated; when the fan blades are damaged and the rotor is unbalanced, the fan should be replaced or the rotor should be calibrated; when the shaft is bent or cracked, the bent shaft should be replaced or corrected; when the transmission belt joint is not good, it should be reconnected; when the base and the core are not tightly fitted, they should be re-reinforced.

The following four items should be checked for electrical aspects: When the motor is running in single phase, the broken wires and poor contact of the lines or windings should be found and repaired; when there is a short circuit or grounding fault in the winding, the short circuit and grounding should be found and repaired; when there is a branch short circuit in the parallel winding, the broken wires should be found and repaired; when the rotor bars or end rings are broken, they should be recast with aluminum or replaced.